MuPDF Explored
Robin Watts
March 27, 2017
Preface
This is the beginnings of a book on MuPDF. It is far from complete, but offers
useful information as far as it goes. We offer it with the latest release of MuPDF
(currently 1.11) in the hopes it will be useful.
Any feedback, corrections or suggestions are welcome. Please visit bugs.
ghostscript.com and open a bug with “MuPDF” as the product, and “Do-
cumentation” as the component.
We will endeavour to make new versions available from the Documentation
section of mupdf.com as they appear.
i
Contents
Preface i
1 Introduction 1
1.1 What is MuPDF? . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Dependencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Quick Start 4
2.1 How to open a document and render some pages . . . . . . . . . 4
3 The Context 5
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3 Custom Allocators . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4 Multi-threading . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.5 Cloning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6 Destruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.7 Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Error handling 14
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2 Throwing exceptions . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.3 Handling exceptions . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5 Reference Counting, Memory Management and The Store 20
5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.2 Reference Counting . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2.1 Implementation . . . . . . . . . . . . . . . . . . . . . . . . 21
5.3 Creating the Store . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.4 Using the store . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4.2 Handling keys . . . . . . . . . . . . . . . . . . . . . . . . . 23
ii
CONTENTS iii
5.4.3 Hashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.4.4 Key storable items . . . . . . . . . . . . . . . . . . . . . . 25
5.4.5 Reap passes . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.5 Scavenging memory allocator . . . . . . . . . . . . . . . . . . . . 26
5.6 Reacting to Out of Memory events . . . . . . . . . . . . . . . . . 27
6 The Document interface 28
6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.2 Opening/Closing a document . . . . . . . . . . . . . . . . . . . . 28
6.3 Handling password protected documents . . . . . . . . . . . . . . 30
6.4 Handling reflowable documents . . . . . . . . . . . . . . . . . . . 30
6.5 Getting Pages from a document . . . . . . . . . . . . . . . . . . . 31
6.6 Anatomy of a Page . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.7 Rendering Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7 The Device interface 37
7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.2 Device Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.1 Line Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.2 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.3 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.2.4 Shadings . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.2.5 Clipping and Masking . . . . . . . . . . . . . . . . . . . . 40
7.2.6 Groups and Transparency . . . . . . . . . . . . . . . . . . 40
7.2.7 Tiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.2.8 Render Flags . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.3 Cookie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.3.1 Detecting errors . . . . . . . . . . . . . . . . . . . . . . . 43
7.3.2 Using the cookie with threads . . . . . . . . . . . . . . . . 43
7.3.3 Using the cookie to control partial rendering . . . . . . . 44
7.4 Device Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
7.5 Inbuilt Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.5.1 BBox Device . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.5.2 Draw Device . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.5.3 Display List Device . . . . . . . . . . . . . . . . . . . . . . 47
7.5.4 PDF Output Device . . . . . . . . . . . . . . . . . . . . . 48
7.5.5 Structured Text Device . . . . . . . . . . . . . . . . . . . 49
7.5.6 SVG Output Device . . . . . . . . . . . . . . . . . . . . . 49
7.5.7 Test Device . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.5.8 Trace Device . . . . . . . . . . . . . . . . . . . . . . . . . 52
8 Building Blocks 53
8.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
8.2 Colorspaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
8.2.1 Basic Colorspaces . . . . . . . . . . . . . . . . . . . . . . 53
8.3 Pixmaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
CONTENTS iv
8.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.3.2 Saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.4 Bitmaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
8.5 Halftones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8.6 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.6.1 Compressed Images . . . . . . . . . . . . . . . . . . . . . 59
8.6.2 Pixmap Images . . . . . . . . . . . . . . . . . . . . . . . . 59
8.7 Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.8 Transforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8.9 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
8.9.1 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
8.9.2 Reference counting . . . . . . . . . . . . . . . . . . . . . . 70
8.9.3 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
8.9.4 Transformation . . . . . . . . . . . . . . . . . . . . . . . . 73
8.9.5 Bounding . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
8.9.6 Stroking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
8.9.7 Walking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
8.10 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
8.10.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
8.10.2 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
8.10.3 Population . . . . . . . . . . . . . . . . . . . . . . . . . . 80
8.10.4 Measurement . . . . . . . . . . . . . . . . . . . . . . . . . 82
8.10.5 Cloning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
8.10.6 Language . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
8.10.7 Implementation . . . . . . . . . . . . . . . . . . . . . . . . 83
8.11 Shadings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.11.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.11.2 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
8.11.3 Bounding . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.11.4 Painting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.11.5 Decomposition . . . . . . . . . . . . . . . . . . . . . . . . 88
9 Display Lists 90
9.0.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
9.0.2 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
9.0.3 Playback . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
9.0.4 Reference counting . . . . . . . . . . . . . . . . . . . . . . 92
9.0.5 Miscellaneous operations . . . . . . . . . . . . . . . . . . . 93
10 The Stream interface 94
10.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
10.2 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
10.3 Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
10.3.1 Reading bytes . . . . . . . . . . . . . . . . . . . . . . . . . 96
10.3.2 Reading objects . . . . . . . . . . . . . . . . . . . . . . . . 98
10.3.3 Reading bits . . . . . . . . . . . . . . . . . . . . . . . . . 99
CONTENTS v
10.3.4 Reading whole streams . . . . . . . . . . . . . . . . . . . . 100
10.3.5 Seeking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
10.3.6 Meta data . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
10.3.7 Destruction . . . . . . . . . . . . . . . . . . . . . . . . . . 103
10.4 Implementing an fz stream . . . . . . . . . . . . . . . . . . . . . 103
11 The Output interface 106
11.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
11.2 Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
11.3 Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
11.3.1 Writing bytes . . . . . . . . . . . . . . . . . . . . . . . . . 108
11.3.2 Writing objects . . . . . . . . . . . . . . . . . . . . . . . . 108
11.3.3 Writing strings . . . . . . . . . . . . . . . . . . . . . . . . 109
11.3.4 Seeking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
11.4 Implementing a fz output . . . . . . . . . . . . . . . . . . . . . . 111
12 Rendered Output Formats 113
12.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
12.2 Band Writers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
12.3 PNM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
12.4 PAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
12.5 PBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
12.6 PKM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
12.7 PNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
12.8 PWG/CUPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
12.8.1 Contone . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
12.8.2 Mono . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
12.9 TGA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
12.10PCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
12.10.1 Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
12.10.2 Mono . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
12.11Postscript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
13 The Image interface 126
13.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
13.2 Standard Image Types . . . . . . . . . . . . . . . . . . . . . . . . 128
13.2.1 Compressed . . . . . . . . . . . . . . . . . . . . . . . . . . 128
13.2.2 Decoded . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
13.2.3 Display List . . . . . . . . . . . . . . . . . . . . . . . . . . 130
13.3 Creating Images . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
13.4 Implementing an Image Type . . . . . . . . . . . . . . . . . . . . 132
13.5 Image Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
14 The Document Handler interface 137
14.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
14.2 Implementing a Document Handler . . . . . . . . . . . . . . . . . 138
CONTENTS vi
14.2.1 Recognize and Open . . . . . . . . . . . . . . . . . . . . . 138
14.2.2 Document Level Functions . . . . . . . . . . . . . . . . . 140
14.2.3 Page Level Functions . . . . . . . . . . . . . . . . . . . . . 143
14.3 Standard Document Handlers . . . . . . . . . . . . . . . . . . . . 146
14.3.1 PDF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
14.3.2 XPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
14.3.3 EPUB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
14.3.4 HTML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
14.3.5 SVG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
14.3.6 Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
14.3.7 CBZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
15 The Document Writer interface 148
15.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
15.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
16 Progressive Mode 153
16.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
16.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
16.2.1 Progressive Streams . . . . . . . . . . . . . . . . . . . . . 154
16.2.2 Rough renderings . . . . . . . . . . . . . . . . . . . . . . . 155
16.2.3 Directed downloads . . . . . . . . . . . . . . . . . . . . . 155
16.2.4 Example implementation . . . . . . . . . . . . . . . . . . 157
17 Fonts 159
18 Build configuration 160
19 PDF Page Manipulation 161
20 PDF Interpreter Details 162
20.1 PDF Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
20.2 PDF Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
20.3 PDF Operator Processors . . . . . . . . . . . . . . . . . . . . . . 162
20.3.1 Run processor . . . . . . . . . . . . . . . . . . . . . . . . 162
20.3.2 Filter processor . . . . . . . . . . . . . . . . . . . . . . . . 162
20.3.3 Buffer processor . . . . . . . . . . . . . . . . . . . . . . . 162
21 XPS Interpreter Details 163
22 EPub Interpreter Details 164
23 SVG Interpreter Details 165
24 MuTool 166
24.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.2 Clean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
CONTENTS vii
24.3 Create . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.4 Draw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.5 Extract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.6 Info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.7 Merge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.8 Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.9 Poster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
24.10Show . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
25 Platform specifics 167
25.1 Android viewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
25.2 Desktop Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
25.2.1 Language bindings . . . . . . . . . . . . . . . . . . . . . . 167
25.2.2 Viewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
25.3 GSView . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
25.4 Javascript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
25.5 Linux/Windows viewer . . . . . . . . . . . . . . . . . . . . . . . . 167
25.5.1 Non-GL version . . . . . . . . . . . . . . . . . . . . . . . . 167
25.5.2 GLFW version . . . . . . . . . . . . . . . . . . . . . . . . 167
A Naming conventions and style 168
Chapter 1
Introduction
1.1 What is MuPDF?
MuPDF is a portable C library for opening, manipulating and rendering do-
cuments in a variety of formats, including PDF, XPS, SVG, e-pub, and many
common image formats.
This core C library provides an API (known as the MuPDF API) that allows a
wide range of actions to be performed on those documents. The exact actions
available depend on the format of the document, but always includes rendering
of those files.
As well as this library, the MuPDF distribution includes various tools built
on top of this API. These tools include simple viewers, tools to manipulate
documents, to add, remove or resize pages, and to extract resources and other
information from the documents. These tools are deliberately kept as ‘thin’ as
possible. The heavy lifting is all performed by the core library, so as to be as
reusable as possible.
Finally, the MuPDF distribution includes bindings to reflect the MuPDF C API
into other languages, such as Java and Javascript.
1.2 License
MuPDF is released under two licenses.
Firstly, it is available under the GNU Afferro General Purpose License (hence-
forth the GNU AGPL). This is a complex license worthy of careful study and
more words than we have space for here. Some key points, however are:
1
CHAPTER 1. INTRODUCTION 2
• You are free to use MuPDF within a piece of software written entirely
for your own use with no problems. The moment you pass that software
to any other person, or make it available to any other person as part of
a “Software as a service” installation, you must abide by the following
terms.
• If you link MuPDF into your own software, then the entirety of that
software must be licensed under the GNU AGPL.
• If you use MuPDF as part of a “Software as a service” installation, then
you must license the entirety of that installation under the GNU AGPL.
• Releasing a piece of software under the GNU AGPL requires you to be
prepared to give full source code to any user that receives a copy of the
software. No charge (other than nominal media costs) may be made for
this.
• You must ensure that all end users of that system have the ability to
update the software with an updated version of MuPDF. This includes
embedded systems.
• Using MuPDF under the GNU AGPL, you receive no warranty and no
support.
There are other terms too, and we strongly recommend that you read the license
in full and understand your obligations under it before developing code based
upon MuPDF.
If you find that you can abide by all the terms of the GNU AGPL, you can use
MuPDF in your own projects without any license fee.
These terms, however, are generally stringent enough that they are inappro-
priate for people producing commercial products - giving the source code to a
commercial product away is generally unacceptable, and the ‘relinking’ require-
ments of the GNU AGPL are too cumbersome for embedded users.
It is for this reason that Artifex (the developers of MuPDF) offer commercial
licenses. Contact sales@artifex.com for a quote tailored to your exact needs.
The Artifex commercial license removes all the onerous terms of the GNU
AGPL, including the need to license your entire app, to give away source, and
to ensure relinking capabilities.
If you find yourself unable to accept and comply with the terms of the GNU
AGPL, and unwilling to obtain a Commercial license from Artifex, you cannot
legally use MuPDF in any software that you distribute.
CHAPTER 1. INTRODUCTION 3
1.3 Dependencies
The core MuPDF library makes use of various software libraries.
Freetype Renderer for various font types.
Harfbuzz OpenType Font shaper built upon freetype, required for e-pub files.
JBig2dec Image decoder for JBIG2 images.
JpegLib Image decoder for JPEG images.
MuJS Javascript engine used for PDF files.
OpenJPEG Image decoder for JPEG2000 images.
ZLib Compression library.
In addition, the MuPDF library can optionally make use of:
OpenSSL Encryption library, required for Digital Signatures support.
Finally, the MuPDF viewer for Linux and Windows can optionally make use of:
Curl An http fetcher used for displaying files as they download.
These libraries are packaged with MuPDF, either in the distribution archives
or as git submodules. From time to time, these libraries may include bug fixes
that have not been accepted back into the upstream repositories. We therefore
strongly recommend using the versions of the libraries that we ship, rather than
any other versions you may find on your system.
Chapter 2
Quick Start
2.1 How to open a document and render some
pages
For a simple example of how to open a document and render some pages, see
docs/example.c.
4
Chapter 3
The Context
3.1 Overview
The core MuPDF library is designed for simplicity, portability, and ease of
integration. For all these reasons, it has no global variables, has no thread
library dependencies, and has a well defined exception system to handle runtime
errors. Nonetheless, in order to be as useful as possible, clearly the library
must have some state and needs to be able to take advantage of multi-threaded
environments.
The solution to these seemingly conflicting requirements is the Context
(fz context).
Every caller to MuPDF should create a Context at the start of its use of the
library, and destroy it at the end. This Context (or one ‘cloned’ from it) will
then be passed in to every MuPDF API call.
Global State At its simplest, the Context contains global settings for the li-
brary. For instance, the levels of Antialiasing used by the text and line
art rendering routines are set in the Context, as is the default style sheet
for Epub or FB2 files. In addition, the library stores its own private
information there too.
Error handling All error handling within MuPDF is done using the fz try/
fz catch constructs; see chapter 4 Error handling for more details.
These constructs can be nested, so rely on an exception stack maintained
within the context. As such it is vitally important that no two threads
use the same context at the same time. See section 3.4 Multi-threading
for more information.
Allocation When embedding MuPDF into a system it is often desirable to
5
CHAPTER 3. THE CONTEXT 6
control the allocators used. A set of allocator functions can be provided
to the Context at creation time, and all allocations will be performed using
these. See chapter 5 Reference Counting, Memory Management and The
Store for more information.
The Store MuPDF uses a memory cache to aid performance, and to avoid re-
peated decoding of resources from the file. The store is maintained using
the context, and shared between a context and its clones. See chapter 5
Reference Counting, Memory Management and The Store for more infor-
mation.
Multi-threading MuPDF does not rely on threading itself, but it can be used
in a multi-threaded environment to give significant performance impro-
vements. Any thread library can be used with MuPDF. A set of locking/
unlocking functions must be passed to the context at creation time, and
the library will use these to ensure it is thread safe. See section 3.4 Multi-
threading for more information.
3.2 Creation
To create a context, use fz new context:
/*
fz_new_context: Allocate context containing global state.
The global state contains an exception stack, resource store,
etc. Most functions in MuPDF take a context argument to be
able to reference the global state. See fz_drop_context for
freeing an allocated context.
alloc: Supply a custom memory allocator through a set of
function pointers. Set to NULL for the standard library
allocator. The context will keep the allocator pointer, so the
data it points to must not be modified or freed during the
lifetime of the context.
locks: Supply a set of locks and functions to lock/unlock
them, intended for multi-threaded applications. Set to NULL
when using MuPDF in a single-threaded applications. The
context will keep the locks pointer, so the data it points to
must not be modified or freed during the lifetime of the
context.
max_store: Maximum size in bytes of the resource store, before
it will start evicting cached resources such as fonts and
images. FZ_STORE_UNLIMITED can be used if a hard limit is not
desired. Use FZ_STORE_DEFAULT to get a reasonable size.
CHAPTER 3. THE CONTEXT 7
Does not throw exceptions, but may return NULL.
*/
fz_context *fz_new_context(const fz_alloc_context *alloc, const
fz_locks_context *locks, unsigned int max_store);
For example, a simple, single threaded program using the standard allocator
can just use:
fz_context *ctx = fz_new_context(NULL, NULL, FZ_STORE_UNLIMITED);
3.3 Custom Allocators
In some circumstances it can be desirable to force all allocations through a set of
‘custom’ allocators. These are defined as an fz alloc context structure whose
address is passed in to fz new context. This structure must exist for the life
time of the returned fz context (and any clones).
typedef struct
{
void *user;
void *(*malloc)(void *, size_t);
void *(*realloc)(void *, void *, size_t);
void (*free)(void *, void *);
} fz_alloc_context;
The malloc, realloc and free function pointers have essentially the same
semantics as the standard malloc, realloc and free standard functions, with
the exceptions that they take an additional initial argument - that of the user
value specified in the fz alloc context.
3.4 Multi-threading
MuPDF itself does not rely on a thread system, but it will make use of one if one
is present. This is crucial to ensure that MuPDF can be called from multiple
threads at once.
A typical example of this might be in a multi-core processor on a printer. We
can interpret the PDF file to a display list, and then render ‘bands’ from that
display list to send to the printer. By using multiple threads we can render
multiple bands at once, thus vastly improving processing times.
In this example, although each thread will be rendering different things, they
will probably share some information - for instance the same font is likely to be
CHAPTER 3. THE CONTEXT 8
used in multiple bands. Rather than have every thread render all the glyphs that
it needs from the font independently, it would be nice if they could collaborate
and share results.
We therefore arrange that data structures such as the font cache can be shared
between the different threads. This, however, brings dangers; what if two thre-
ads try to write to the same data structure at once?
To save this being a problem, we rely on the user providing some locking functi-
ons for us.
/*
Locking functions
MuPDF is kept deliberately free of any knowledge of particular
threading systems. As such, in order for safe multi-threaded
operation, we rely on callbacks to client provided functions.
A client is expected to provide FZ_LOCK_MAX number of mutexes,
and a function to lock/unlock each of them. These may be
recursive mutexes, but do not have to be.
If a client does not intend to use multiple threads, then it
may pass NULL instead of a lock structure.
In order to avoid deadlocks, we have one simple rule
internally as to how we use locks: We can never take lock n
when we already hold any lock i, where 0 <= i <= n. In order
to verify this, we have some debugging code, that can be
enabled by defining FITZ_DEBUG_LOCKING.
*/
typedef struct
{
void *user;
void (*lock)(void *user, int lock);
void (*unlock)(void *user, int lock);
} fz_locks_context;
enum {
...
FZ_LOCK_MAX
};
If MuPDF is to be used in a multi-threaded environment, then the user is
expected to define FZ LOCK MAX locks (currently 4, though this may change in
future), together with functions to lock and unlock them.
In pthreads, a lock might be implemented by pthread mutex t. In windows,
either Mutex or a CriticalSection might be used (the latter being more lig-
CHAPTER 3. THE CONTEXT 9
htweight).
These locks are not assumed to be recursive (though recursive locks will work
just fine).
To avoid deadlocks, MuPDF guarantees never to take lock n if that thread
already holds lock m (for n ¿ m ).
There are 3 simple rules to follow when using MuPDF in a multi threaded
environment:
1. No simultaneous calls to MuPDF in different threads are allowed
to use the same context.
Most of time it is simplest just to use a different context for every thread;
just create a new context at the same time as you create the thread. See
section 3.5 Cloning for more information.
2. No simultaneous calls to MuPDF in different threads are allowed
to use the same document.
Only one thread can be accessing an document at a time. Once display
lists are created from that document, multiple threads can operate on
them safely.
The document can safely be used from several different threads as long as
there are safeguards in place to prevent the usages being simultaneous.
3. No simultaneous calls to MuPDF in different threads are allowed
to use the same device.
Calling a device simultaneously from different threads will cause it to get
confused and may crash. Calling a device from several different threads
is perfectly acceptable as long as there are safeguards in place to prevent
the calls being simultaneous.
3.5 Cloning
The context contains the exception stack for the fz try/fz catch constructs.
As such trying to use the same context from multiple threads at the same time
will lead to crashes.
The solution to this is to ‘clone’ the context. Each clone will share the same
underlying store (and will inherit the same settings, such as allocators, locks
etc), but will have its own exception handle. Other settings, such as anti-alias
levels, will be inherited from the original at the time of cloning, but can be
changed to be different if required.
For example, in a viewer application, we might want to have a background
process that runs through the file generating page thumbnails. In order for this
CHAPTER 3. THE CONTEXT 10
not to interfere with the foreground process, we would clone the context, and
use the cloned context in the thumbnailing thread. We might choose to disable
anti-aliasing for the thumbnailing thread to trade quality for speed.
Any images decoded for the thumbnailing thread would live on in the store
though, and would hence be available should the viewers normal render opera-
tions need them.
To clone a context, use fz clone context:
/*
fz_clone_context: Make a clone of an existing context.
This function is meant to be used in multi-threaded
applications where each thread requires its own context, yet
parts of the global state, for example caching, is shared.
ctx: Context obtained from fz_new_context to make a copy of.
ctx must have had locks and lock/functions setup when created.
The two contexts will share the memory allocator, resource
store, locks and lock/unlock functions. They will each have
their own exception stacks though.
Does not throw exception, but may return NULL.
*/
fz_context *fz_clone_context(fz_context *ctx);
For example:
fz_context *worker_ctx = fz_clone_context(ctx);
In order for cloned contexts to work safely, they rely on being able to
take locks around certain operations to make them atomic. Accordingly,
fz clone context will return NULL (to indicate failure) if the base context
did not have locking functions defined.
3.6 Destruction
Once you have finished with an fz context (either your original one, or a
‘cloned’ one) you can destroy it using fz drop context.
/*
fz_drop_context: Free a context and its global state.
The context and all of its global state is freed, and any
buffered warnings are flushed (see fz_flush_warnings). If NULL
is passed in nothing will happen.
CHAPTER 3. THE CONTEXT 11
Does not throw exceptions.
*/
void fz_drop_context(fz_context *ctx);
For example:
fz_drop_context(ctx);
3.7 Tuning
Some of MuPDF’s functionality relies on heuristics to make decisions. Rather
than hard code these decisions in the library code, the tuning context allows
callers to override the defaults with their own ‘tuned’ versions.
Currently, we have just 2 calls defined here, both to do with image handling,
but this may expand in future.
The first tuning function enables fine control over how much of an image MuPDF
should decode if it only requires a subarea:
/*
fz_tune_image_decode_fn: Given the width and height of an image,
the subsample factor, and the subarea of the image actually
required, the caller can decide whether to decode the whole image
or just a subarea.
arg: The caller supplied opaque argument.
w, h: The width/height of the complete image.
l2factor: The log2 factor for subsampling (i.e. image will be
decoded to (w>>l2factor, h>>l2factor)).
subarea: The actual subarea required for the current operation.
The tuning function is allowed to increase this in size if required.
*/
typedef void (fz_tune_image_decode_fn)(void *arg, int w, int h, int
l2factor, fz_irect *subarea);
Having defined a function of this type to implement the desired strategy, it can
be set into the context using:
/*
fz_tune_image_decode: Set the tuning function to use for
image decode.
CHAPTER 3. THE CONTEXT 12
image_decode: Function to use.
arg: Opaque argument to be passed to tuning function.
*/
void fz_tune_image_decode(fz_context *ctx, fz_tune_image_decode_fn
*image_decode, void *arg);
The second function allows fine control over the scaling used when images are
scaled:
/*
fz_tune_image_scale_fn: Given the source width and height of
image, together with the actual required width and height,
decide whether we should use mitchell scaling.
arg: The caller supplied opaque argument.
dst_w, dst_h: The actual width/height required on the target device.
src_w, src_h: The source width/height of the image.
Return 0 not to use the Mitchell scaler, 1 to use the Mitchell
scaler. All
other values reserved.
*/
typedef int (fz_tune_image_scale_fn)(void *arg, int dst_w, int dst_h,
int src_w, int src_h);
Having defined a function of this type to implement the desired strategy, it can
be set into the context using:
/*
fz_tune_image_scale: Set the tuning function to use for
image scaling.
image_scale: Function to use.
arg: Opaque argument to be passed to tuning function.
*/
void fz_tune_image_scale(fz_context *ctx, fz_tune_image_scale_fn
*image_scale, void *arg);
3.8 Summary
The basic usage of Contexts is as follows:
1. Call fz new context to create a context. Pass in any custom allocators
CHAPTER 3. THE CONTEXT 13
required. If you wish to use MuPDF from multiple threads at the same
time, you must also pass in locking functions. Set the store size appropri-
ately.
2. Call fz clone context to clone the context as many times as you need;
typically once for each ‘worker’ thread.
3. Perform the operations required using MuPDF within fz try/fz catch
constructs.
4. Call fz drop context with each cloned context.
5. Call fz drop context with the original context.
Things to remember:
1. A fz context can only be used in 1 thread at a time.
2. A fz document can only be used in 1 thread at a time.
3. A fz device can only be used in 1 thread at a time.
4. A fz context shares the store with all the fz contexts cloned from it.
Chapter 4
Error handling
4.1 Overview
MuPDF handles all its errors using an exception system. This is superficially
similar to C++ exceptions, but (as MuPDF is written in C) it is implemented
using macros that wrap the setjmp/longjmp standard C functions.
It is probably best not to peek behind the curtain, and just to think of these
constructs as being extensions to the language. Indeed, we have worked very
hard to ensure that the complexities involved are minimised.
Unless otherwise specified, all MuPDF API functions can throw exceptions, and
should therefore be called within an fz try/fz always/fz catch construct.
The general anatomy of such a construct is as follows:
fz_try(ctx)
{
/* Do stuff in here that might throw an exception.
* NEVER return from here. ’break’ can be used to
* continue execution (either in the always block or
* after the catch block). */
}
fz_always(ctx)
{
/* Anything in here will always be executed, regardless
* of whether the fz_try clause exited normally, or an
* exception was thrown. */
}
fz_catch(ctx)
{
/* This block will execute if (and only if) anything in
* the fz_try block calls fz_throw. We should clean up
14
CHAPTER 4. ERROR HANDLING 15
* anything we need to. If we are in a nested fz_try/
* fz/catch block, we can call fz_rethrow to propagate
* the error to the enclosing catch. */
}
The fz always block is completely optional. The following is perfectly valid:
fz_try(ctx)
{
/* Do stuff here */
}
fz_catch(ctx)
{
/* Clean up from errors here */
}
In an ideal world, that would be all there is to it. Unfortunately, there are 2
wrinkles.
The first one, relatively simple, is that you must not return from within a fz try
block. To do so will corrupt the exception stack and cause problems and crashes.
To mitigate this, you can safely break out of the fz try, and execution will pass
into the fz always block (if there is one, or continue after the fz catch block
if not).
The second one, is more convoluted. If you do not wish to understand the long
and complex reasons behind this, skip forward to the summary and just follow
the rules there.
As stated before fz try/ fz catch are implemented using setjmp/longjmp,
and these can ‘lose’ changes to variables.
For example:
house_t *build_house(fz_context *ctx)
{
walls_t *w = NULL;
roof_t *r = NULL;
house_t *h = NULL;
fz_try(ctx)
{
w = make_walls();
r = make_roof();
h = combine(w, r); /* Note, NOT: return combine(w,r); */
}
fz_always(ctx)
{
drop_walls(w);
drop_roof(r);
CHAPTER 4. ERROR HANDLING 16
}
fz_catch(ctx)
{
return NULL; /* Or fz_rethrow if we’re nested */
}
return h;
}
In the above code (as well as throughout MuPDF), we follow the convention
that destructors always accept NULL. This makes cleanup code much simpler.
Reading through this code, it is fairly obvious what will happen if everything
works correctly. First we’ll make some walls, w, and a roof, r. Then we combine
the walls and the roof, to get our house, h. Next we tidy up the walls and the
roof, and we return the completed house to our caller.
It’s more interesting to consider what will happen if we have failures.
First let’s consider what happens if the make walls fails. This will fz throw an
exception, and control will jump immediately to the fz always. This will drop
w and r (both of which are still NULL). The fz catch can then handle the error,
either by returning NULL, to indicate failure, or perhaps by fz rethrowing the
error to an enclosing fz try/ fz catch construct. No problems there.
So what happens when the failure occurs in make roof fails? Let’s run through
the code again.
This time, make walls succeeds, and w is set to this new value. Then make roof
fails, fz throwing an exception, and control will jump immediately to the
fz always. This will then try to drop w (now a valid value) and r (which is still
NULL). The fz catch can then handle the error, either by returning NULL, to
indicate failure, or perhaps by fz rethrowing the error to an enclosing fz try/
fz catch construct. All sounds quite plausible.
Unfortunately, if you try it, on some systems you will find that you have a
memory leak (or worse). When drop walls is called, sometimes you will find
that w has ‘lost’ its value.
This is due to an obscure part of the C specification that states that any changes
to local variables made between a setjmp and a longjmp can be lost.
In fz try/ fz catch terms, this means that any local variables set within the
fz try block can be ‘lost’ when either fz always or fz catch are reached.
Fortunately, there is a fix for this, fz var. By calling fz var(w); we can
‘protect’ variable w from such unwanted behaviour.
It’s not really necessary to know how this works, but for those interested, a quick
explanation. The ‘loss’ of the value occurs because the compiler can postpone
writing the value back into the storage location for the variable (or can choose to
just hold it in a register). The call to fz var passes the address of the variable
CHAPTER 4. ERROR HANDLING 17
out of scope; this forces the compiler not to hold it in a register. Further, the
compiler has no way of knowing whether any functions it call might access that
location, so it needs to make sure that the variable value is written back on every
function call - such as longjmp. Hence the variable is magically protected.
Calls to fz var are very low cost (but are not NOPs), so erring on the side of
caution and calling fz var on more than you need to will probably not hurt.
A corrected version of the above example is therefore:
house_t *build_house(fz_context *ctx)
{
walls_t *w = NULL;
roof_t *r = NULL;
house_t *h = NULL;
fz_var(w);
fz_var(r);
fz_try(ctx)
{
w = make_walls();
r = make_roof();
h = combine(w, r); /* Note, NOT: return combine(w,r); */
}
fz_always(ctx)
{
drop_walls(w);
drop_roof(r);
}
fz_catch(ctx)
{
return NULL; /* Or fz_rethrow if we’re nested */
}
return h;
}
4.2 Throwing exceptions
Most client code need never worry about anything more than catching excep-
tions thrown by the core core. If you are implementing your own devices or
extending the core of MuPDF, then you will need to know how to generate (and
pass on) your own exceptions.
An exception is constructed and thrown from an integer code and a printf like
string:
enum
CHAPTER 4. ERROR HANDLING 18
{
FZ_ERROR_NONE = 0,
FZ_ERROR_GENERIC = 1,
FZ_ERROR_SYNTAX = 2,
FZ_ERROR_TRYLATER = 3,
FZ_ERROR_ABORT = 4,
FZ_ERROR_COUNT
};
void fz_throw(fz_context *ctx, int errcode, const char *, ...);
In almost all cases, you should be using FZ ERROR GENERIC, for example:
fz_throw(ctx, FZ_ERROR_GENERIC, "Failed to open file ’%s’", filename);
4.3 Handling exceptions
Once you have caught an exception, most code will simply tidy up any loose
resources (to prevent leaks), and rethrow the exception up to a higher layer
handler.
At the top level of the program, clearly this is not an option. The catch clause
needs to return the error using whatever process the calling program is using
for error handling.
Details of the message from the caught error can be read using:
const char *fz_caught_message(fz_context *ctx);
The error will remain readable in this way until the next use of fz try/fz catch
on that same context.
Some code may choose to swallow the error and retry the same code again in a
different manner. To facilitate this, we can find out the type of error using:
int fz_caught(fz_context *ctx);
See section 4.2 Throwing exceptions for a list of the possible exception types.
To simplify the job of deciding whether to pass on exceptions of a given type,
we have a convenience function that with rethrow just a particular type.:
void fz_rethrow_if(fz_context *ctx, int errcode);
CHAPTER 4. ERROR HANDLING 19
4.4 Summary
The basic exception handling rules are as follows:
1. All MuPDF functions except those that explicitly state otherwise, throw
exceptions on errors, and must therefore be called from within an fz try/
fz catch construct.
2. A fz try block must be paired with an fz catch block, and optionally
an fz always block can appear between them.
3. Never return from an fz try block.
4. An fz try block will terminate when control reaches the end of the block,
or when break is called.
5. Any variable that is changed within an fz try block may lose its value if
an exception occurs, unless protected by fz var call.
6. The contents of the fz always block will always be executed (after the
fz try block and before the fz catch block, if appropriate).
7. If an exception is thrown during the fz try block, control will jump to
the fz always block (if there is one) and then continue to the fz catch
block.
Chapter 5
Reference Counting,
Memory Management and
The Store
5.1 Overview
While MuPDF is running, it holds various objects in memory, and passes them
between its various components. For instance, MuPDF might read a path defi-
nition in in the PDF interpreter, and pass it first into the display list and then
on into the renderer.
To avoid needless copying of data, a reference counting scheme is used. Each
significant object has a reference count, so that when one area of the code
retains a reference to something (perhaps the display list), the data need not
be copied wholesale. In the above example, the PDF interpreter might hold
one reference, and first the display list and then the renderer might take others.
Some references are held just for a short length of time, but others can persist
for a much longer period.
During the course of displaying files, MuPDF loads various resources into me-
mory, such as fonts and images. By holding these resources in memory throug-
hout the processing of the file we can avoid reloading them each time they are
required.
As the document is rendered, more memory is needed to hold rendered versions
of glyphs from the font, or decoded versions of images. By keeping these decoded
versions around in memory, we can avoid the need to redecode them the next
time we need the same glyph, or the same image.
20
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE21
Keeping all this data around can end up using a large amount of memory, which
may be unfeasible for some systems. Equally, not keeping any of it around will
result in a drastic performance drop.
The solution is to keep as much around as can conveniently fit in memory.
MuPDF achieves this using a mechanism known as “The Store”.
The Store is a mechanism for holding blocks of data likely to be reusable. Whe-
never MuPDF needs such a block of data, it checks the Store to see if the data
is there already - if it is, it can be instantly reused. If not the code forms the
data itself, and then puts it into the store.
The MuPDF allocation code is tied into the store, so that if an allocation ever
fails, objects are evicted from the store, and the allocation retried. This ‘sca-
venging’ of memory means that we can safely keep lots of cached data around
without ever worrying that it will cause us to run out of memory.
5.2 Reference Counting
As mentioned above, most MuPDF objects are reference counted. This means
that on creation (typically with an fz
new ... call), they have a reference count
of 1. Think of these object pointers as ‘handles’.
If a ‘copy’ of the object is required, a new handle can be generated using the
appropriate fz keep ... call. This is a very low cost operation that just
involves incrementing the reference count, so no physical copying of the data is
involved. Accordingly it is vital that objects that have multiple handles do not
have their contents altered.
Once a reference is finished with, it should be disposed of using the appropriate
fz drop ... call. This is true regardless of whether the handle was created by
a fz new ... or a fz keep ... call. This drops the reference count by 1.
Once the reference count hits 0, the storage used by the object is freed.
As an implementation detail, certain objects within MuPDF are allocated stati-
cally and have a reference count of -1. These are unaffected by reference counting
operations, and will never be freed. Nonetheless, these should be treated exactly
as for normal objects and kept/dropped as usual.
5.2.1 Implementation
These keep and drop calls for simple objects are generally implemented by using
one of a set of standard functions. There are a range of these, depending on
the expected size of the reference counts, and all handle the locking required to
ensure thread safety:
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE22
void *fz_keep_imp(fz_context *ctx, void *p, int *refs);
void *fz_keep_imp8(fz_context *ctx, void *p, int8_t *refs);
void *fz_keep_imp16(fz_context *ctx, void *p, int16_t *refs);
int fz_drop_imp(fz_context *ctx, void *p, int *refs);
int fz_drop_imp8(fz_context *ctx, void *p, int8_t *refs);
int fz_drop_imp16(fz_context *ctx, void *p, int16_t *refs);
As an example, an fz path structure is defined as:
typedef struct {
int8_t refs;
} fz_path;
and thus appropriate keep and drop functions can be defined simply:
fz_path *fz_keep_path(fz_context *ctx, fz_path *path)
{
return fz_keep_imp8(ctx, &path->refs);
}
void fz_drop_path(fz_context *ctx, fz_path *path)
{
if (!fz_drop_imp8(ctx, &path->refs))
return;
<code to free the contents of the path structure>
}
More complex variations of these functions are available to cope with ‘storable’
objects, and still more complex versions to cope with ‘key storable’ objects -
these are explained in the following sections.
However they are implemented, these objects all look basically the same to most
users - they can simply be ‘kept’ and ‘dropped’ as required.
5.3 Creating the Store
The Store is created as part of the fz new context call, (see the Context chap-
ter) and is shared with any contexts obtained with fz clone context. The
‘store limit’ is specified as a byte size as part of this call. A special value of
FZ STORE UNLIMITED (0) is used to indicate that no amount of memory is too
much.
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE23
5.4 Using the store
5.4.1 Overview
Every “storable piece of information” in MuPDF is held in a data structure that
begins with an fz storable structure. Rather than repeatedly say “a storable
piece of information”, we shall henceforth just say “an fz storable”.
MuPDF uses reference counting for most of its data structures (see section 5.2
Reference Counting), and fz storables are no exception.
Whenever MuPDF needs to use a fz storable, it first checks to see if there is
one in the Store already. It does this by forming a unique ‘key’ and scanning
the Store for an object of a given type, with that key. If the object exists within
the Store, the fact that the object has been used is noted, a reference is taken,
and returned to the caller.
If no reference is returned, the code creates its own version of the fz storable.
It calculates its size, and puts it into the Store, together with the same key as
before. The Store takes a reference to the object, links it into its data structure,
and updates its running total of the size of all the objects within it.
If placing a new object into the store would take it over the limit, it runs through
and looks for the least recently used objects to evict to bring the limit down.
In order for an object to be considered for eviction, their refcount must be 1.
We know that the Store is holding 1 reference to the object - if anything else is,
then removing it from the Store won’t actually save us any memory.
Regardless of whether the Store can be reduced to a suitable size, the object is
always placed into the store. This ensures that the Store’s figure for “amount
of memory used by fz storable’s” remains correct (thus ensuring that should
objects become evictable, the store size will fall correctly). It also does no
harm, because clearly we have managed to allocate enough memory to form the
fz storable in the first place.
Regardless of whether a caller finds the object in the Store, or has to store it
itself, it then proceeds identically. It uses the object for whatever purpose it
needed it, and then calls the appropriate fz drop function to lose its reference.
The object will live on in the Store until it needs to be evicted to make room.
5.4.2 Handling keys
As discussed above, the Store is basically a set of key/value pairs. While the
values are always fz storables, the keys can be of many different types, due
to coming from many disparate parts of the system.
Accordingly, we need a mechanism to allow us to safely know what ‘type’ a
given key is, and to compare 2 keys of identical type.
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE24
We solve this, by using an fz store type structure:
typedef struct fz_store_type_s
{
int (*make_hash_key)(fz_context *ctx, fz_store_hash *, void *);
void *(*keep_key)(fz_context *,void *);
void (*drop_key)(fz_context *,void *);
int (*cmp_key)(fz_context *ctx, void *, void *);
void (*print)(fz_context *ctx, fz_output *out, void *);
int (*needs_reap)(fz_context *ctx, void *);
} fz_store_type;
We will have just one instance of this for each type - normally a static const
structure defined in the code. Whenever we insert (or lookup) something in the
store, we pass the address of that ‘types’ structure.
We only compare items if they have the same type pointer, and any comparison
is done using the cmp key function pointer therein. In common with normal C
idioms, 0 means match, non zero means different.
The keep key and drop key entries are used to implement reference counting
of keys. Because keys can be an amalgam of several reference counted objects,
the keep and drop functions provided here can take and drop these in sync.
The print function is purely for debugging purposes as part of calls to
fz print store - it should generate a human readable summary of the key
to the given fz output stream.
The make hash key and needs reap functions are explained in the following
subsections.
5.4.3 Hashing
In order to ensure the Store performs well, we must ensure that certain processes
run efficiently - notably searching for an existing entry, insertion and deletion.
Accordingly, the Store is implemented based on a hash table. For every ‘key’,
we need to be able to form a hash, but this process is complicated slightly by
the fact that every different fz storable has a different type for the key.
We solve this by having the make hash key member of the fz store type struc-
ture convert whatever its key data is into a common structure:
typedef struct fz_store_hash_s
{
fz_store_drop_fn *drop;
union
{
struct
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE25
{
const void *ptr;
int i;
} pi;
struct
{
const void *ptr;
int i;
fz_irect r;
} pir;
struct
{
int id;
float m[4];
} im;
} u;
} fz_store_hash;
The caller will always arrange for this structure to be zero filled on entry to
the make hash key call. On exit, it should have been updated with the key
details. Implementers may extend the union found in this structure as required,
though ideally the size of the overall structure should be minimised to avoid
unnecessary work.
Once the Store has formed a fz store hash it can then generate the required
hash for the hashtable as required.
5.4.4 Key storable items
Some objects can be used both as values within the Store, and as a component
of keys within the Store. We refer to these objects as “key storable” objects.
In this case, we need to take additional care to ensure that we do not end
up keeping an item within the store, purely because its value is referred to by
another key in the store.
An example of this are fz images in PDF files. Each fz image is placed into
the Store to enable it to be easily reused. When the image is rendered, a pixmap
is generated from the image, and the pixmap is placed into the Store so it can be
reused on subsequent renders. The image forms part of the key for the pixmap.
When we close the pdf document (and any associated pages/display lists etc),
we drop the images from the Store. This may leave us in the position of the
images having non-zero reference counts purely because they are used as part
of the keys for the pixmaps.
We therefore use special reference counting functions to implement these
fz key storable items, fz keep key storable and fz drop key storable
rather than the more usual fz keep storable and fz drop storable.
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE26
The sole difference is that these enable us to store the number of referen-
ces to these items that are used in keys. This is achieved by callers taking
and dropping references for use in keys with fz keep key storable key and
fz drop key storable key.
This means that key storable items need to provide two sets of keep and drop
functions, one for ‘normal’ callers, and one for use during key handling. For
example:
fz_image *fz_keep_image(fz_context *ctx, fz_image *image);
void fz_drop_image(fz_context *ctx, fz_image *image);
fz_image *fz_keep_image_store_key(fz_context *ctx, fz_image *image);
void fz_drop_image_store_key(fz_context *ctx, fz_image *image);
The purpose of this extra work is to allow us to spot when we may need to
check the Store for ‘dead’ entries - those that can never be ‘found’ by looking
in the store.
5.4.5 Reap passes
When the number of references to a key storable object equals the number of
references to an object from keys in the Store, we know that we can remove all
the items which have that object as part of the key. This is done by running a
pass over the store, ‘reaping’ those items.
If a key does not consist of any storable objects, then the needs reap entry in its
fz store type can safely be left as NULL. If it does, however, it must provide
an implementation to check whether a reap pass is required. Essentially this
needs to check if any of its constituent fz key storable objects need reaping,
which can be done by a call to:
int fz_key_storable_needs_reaping(fz_context *ctx, const fz_key_storable
*ks);
Reap passes are slower than we would like as they touch every item in the
store. We therefore provide a way to ‘batch’ such reap passes together, using
fz defer reap start and fz defer reap end to bracket a region in which
many may be triggered.
5.5 Scavenging memory allocator
All allocations within MuPDF (and its sub-libraries) call fz malloc and family.
These functions ultimately call down to the custom allocator functions passed
CHAPTER 5. REFERENCE COUNTING, MEMORY MANAGEMENT AND THE STORE27
into the fz new context call (or to malloc and family if no custom allocators
were supplied). (See chapter 3 The Context for details).
If a call to the underlying custom allocator fails, MuPDF will automatically seek
to evict the least recently used objects from the store that are not currently being
used, and then will retry the allocation. This can happen several times, with
more and more objects being freed between each attempt.
Allocation failures are therefore only fatal to MuPDF if there are no remaining
objects to be freed in the store.
This ‘just in time’ scavenging of memory means that the store limit can safely
be set to a high level (or to be unlimited), and MuPDF will still operate within
safe bounds.
5.6 Reacting to Out of Memory events
As a last resort, applications using MuPDF can react to low memory events by
changing their strategy. For example, if we fail to render a band of data due to
an allocation failure, we might back off and try a smaller band size. Alternati-
vely, we might choose to dispense with the display list, and to reinterpret the
underlying file directly each time, trading speed for memory.
To this end, all exceptions thrown due to allocation failures have the
FZ ERROR OOM type, enabling callers to easily distinguish them using fz caught
and to react accordingly.
Chapter 6
The Document interface
6.1 Overview
Although MuPDF handles multiple different file formats, it offers a unified API
for dealing with them. The fz document API allows all the common operations
to be performed on a document, hiding the implementation specifics away from
the caller.
Not all functions are available on all document types (for instance, JPEG files
do not support annotations), but the API returns sane values.
6.2 Opening/Closing a document
The simplest way to load a document is to load it from the local filing system:
/*
fz_open_document: Open a PDF, XPS or CBZ document.
Open a document file and read its basic structure so pages and
objects can be located. MuPDF will try to repair broken
documents (without actually changing the file contents).
The returned fz_document is used when calling most other
document related functions.
filename: a path to a file as it would be given to open(2).
*/
fz_document *fz_open_document(fz_context *ctx, const char *filename);
28
CHAPTER 6. THE DOCUMENT INTERFACE 29
For embedded systems, or secure applications, the use of a local filing system
may be inappropriate, so an alternative is available whereby documents can
be opened from an fz stream. See chapter 10 The Stream interface for more
details on fz streams.
/*
fz_open_document_with_stream: Open a PDF, XPS or CBZ document.
Open a document using the specified stream object rather than
opening a file on disk.
magic: a string used to detect document type; either a file name or
mime-type.
*/
fz_document *fz_open_document_with_stream(fz_context *ctx, const char
*magic, fz_stream *stream);
Almost any data source can be wrapped up as an fz stream; see chapter 10
The Stream interface for more details.
In common with most other objects in MuPDF, fz documents are reference
counted:
/*
fz_keep_document: Keep a reference to an open document.
Does not throw exceptions.
*/
fz_document *fz_keep_document(fz_context *ctx, fz_document *doc);
/*
fz_drop_document: Release an open document.
The resource store in the context associated with fz_document
is emptied, and any allocations for the document are freed when
the last reference is dropped.
Does not throw exceptions.
*/
void fz_drop_document(fz_context *ctx, fz_document *doc);
Once the last reference to the document is dropped, all resources used by that
document will be released, including those in the Store.
CHAPTER 6. THE DOCUMENT INTERFACE 30
6.3 Handling password protected documents
Some document types (such as PDF) can require passwords to allow the file
to be opened. After you have obtained an fz document, you should therefore
check whether it needs a password using fz needs password:
/*
fz_needs_password: Check if a document is encrypted with a
non-blank password.
Does not throw exceptions.
*/
int fz_needs_password(fz_context *ctx, fz_document *doc);
If a password is required, you can supply one using fz authenticate password:
/*
fz_authenticate_password: Test if the given password can
decrypt the document.
password: The password string to be checked. Some document
specifications do not specify any particular text encoding, so
neither do we.
Does not throw exceptions.
*/
int fz_authenticate_password(fz_context *ctx, fz_document *doc, const
char *password);
6.4 Handling reflowable documents
Some document types (such as Epub) require the contents to be laid out before
they can be rendered. This is done by calling fz layout document:
/*
fz_layout_document: Layout reflowable document types.
w, h: Page size in points.
em: Default font size in points.
*/
void fz_layout_document(fz_context *ctx, fz_document *doc, float w,
float h, float em);
Any non-reflowable document types (such as PDF) will ignore this layout re-
quest. The results of the layout will depend both upon a target width and
CHAPTER 6. THE DOCUMENT INTERFACE 31
height, a given font size, the CSS styles in effect. Documents can be laid out
multiple times to allow changes in these properties to take effect.
MuPDF provides its own default CSS style sheet, but this can be overridden by
the user CSS style sheet in the context:
/*
fz_user_css: Get the user stylesheet source text.
*/
const char *fz_user_css(fz_context *ctx);
/*
fz_set_user_css: Set the user stylesheet source text for use with
HTML and EPUB.
*/
void fz_set_user_css(fz_context *ctx, const char *text);
The user CSS style sheet is supplied as a null terminated C string.
When the CSS or the screen size is changed, and the document relaid out,
content moves. In order for applications to be able to not lose the readers place,
MuPDF offers a mechanism for making a bookmark and then looking it up
again after the content has been laid out to a new position.
/*
Create a bookmark for the given page, which can be used to find the
same location after the document has been laid out with different
parameters.
*/
fz_bookmark fz_make_bookmark(fz_context *ctx, fz_document *doc, int
page);
/*
Find a bookmark and return its page number.
*/
int fz_lookup_bookmark(fz_context *ctx, fz_document *doc, fz_bookmark
mark);
6.5 Getting Pages from a document
Once you have a laid out document, you presumably want to be able to do
something with it. The first thing to know is how many pages it contains. This
is achieved by calling fz count pages:
/*
fz_count_pages: Return the number of pages in document
CHAPTER 6. THE DOCUMENT INTERFACE 32
May return 0 for documents with no pages.
*/
int fz_count_pages(fz_context *ctx, fz_document *doc);
For document types like images, they appear as a single page. If you forget to
lay out a reflowable document, this will trigger a layout for a default size and
return the required number of pages.
Once you know how many pages there are, you can fetch the fz page object for
each page required:
/*
fz_load_page: Load a page.
After fz_load_page is it possible to retrieve the size of the
page using fz_bound_page, or to render the page using
fz_run_page_*. Free the page by calling fz_drop_page.
number: page number, 0 is the first page of the document.
*/
fz_page *fz_load_page(fz_context *ctx, fz_document *doc, int number);
The pages of a document with n pages are numbered from 0 to n -1.
In common with most other object types, fz pages are reference counted:
/*
fz_keep_page: Keep a reference to a loaded page.
Does not throw exceptions.
*/
fz_page *fz_keep_page(fz_context *ctx, fz_page *page);
/*
fz_drop_page: Free a loaded page.
Does not throw exceptions.
*/
void fz_drop_page(fz_context *ctx, fz_page *page);
Once the last reference to a page is dropped, the resources it consumes are all
released automatically.
6.6 Anatomy of a Page
In MuPDF terminology (largely borrowed from PDF) Pages consist of Page
Contents, Annotations, and Links.
CHAPTER 6. THE DOCUMENT INTERFACE 33
Page Contents (or just Contents) are typically the ordinary printed matter that
you would get on a page; the text, illustrations, any headers or footers, and
maybe some printers marks.
Annotations are normally extra information that is overlaid on the top of these
page contents. Examples include freehand scribbles on the page, highlights/
underlines/strikeouts overlaid on the text, sticky notes etc. Annotations are
typically added to a document by people reading the document after it has
been published rather than by the original author.
Annotations can be enumerated from the page one at a time, by first calling
fz first annot, and then fz next annot:
/*
fz_first_annot: Return a pointer to the first annotation on a page.
Does not throw exceptions.
*/
fz_annot *fz_first_annot(fz_context *ctx, fz_page *page);
/*
fz_next_annot: Return a pointer to the next annotation on a page.
Does not throw exceptions.
*/
fz_annot *fz_next_annot(fz_context *ctx, fz_annot *annot);
Annotations are reference counted and can be kept and dropped as usual. They
can also be bounded, by passing a rectangle to fz bound annot:
/*
fz_bound_annot: Return the bounding rectangle of the annotation.
Does not throw exceptions.
*/
fz_rect *fz_bound_annot(fz_context *ctx, fz_annot *annot, fz_rect *rect);
On return, the rectangle is populated with the bounding box of the annotation.
Links describe ‘active’ regions on the page; if the user ‘clicks’ within such a
region typically the viewer should respond. Some links move to other places in
the document, others launch external clients such as mail or web sites.
The links on a page can be read by calling fz load links:
/*
fz_load_links: Load the list of links for a page.
Returns a linked list of all the links on the page, each with
its clickable region and link destination. Each link is
CHAPTER 6. THE DOCUMENT INTERFACE 34
reference counted so drop and free the list of links by
calling fz_drop_link on the pointer return from fz_load_links.
page: Page obtained from fz_load_page.
*/
fz_link *fz_load_links(fz_context *ctx, fz_page *page);
This returns a linked list of fz link structures. link->next gives the next one
in the chain.
6.7 Rendering Pages
To render a page, you first need to know how big it is. This can be discovered
by calling fz bound page, passing an fz rect in to be populated:
/*
fz_bound_page: Determine the size of a page at 72 dpi.
Does not throw exceptions.
*/
fz_rect *fz_bound_page(fz_context *ctx, fz_page *page, fz_rect *rect);
MuPDF operates on page contents (and annotations) by processing them to a
Device. There are various different devices in MuPDF (and you can implement
your own). See chapter 7 The Device interface for more information. For now,
just consider devices to be things that are called with each of the graphical
items on the page in turn.
The simplest way to process a page is to call fz run page:
/*
fz_run_page: Run a page through a device.
page: Page obtained from fz_load_page.
dev: Device obtained from fz_new_*_device.
transform: Transform to apply to page. May include for example
scaling and rotation, see fz_scale, fz_rotate and fz_concat.
Set to fz_identity if no transformation is desired.
cookie: Communication mechanism between caller and library
rendering the page. Intended for multi-threaded applications,
while single-threaded applications set cookie to NULL. The
caller may abort an ongoing rendering of a page. Cookie also
communicates progress information back to the caller. The
fields inside cookie are continually updated while the page is
CHAPTER 6. THE DOCUMENT INTERFACE 35
rendering.
*/
void fz_run_page(fz_context *ctx, fz_page *page, fz_device *dev, const
fz_matrix *transform, fz_cookie *cookie);
This will cause each graphical object from the page contents and annotations
in turn to be transformed, and fed to the device.
For finer control, you may wish to run the page contents, and the annotations
separately:
/*
fz_run_page_contents: Run a page through a device. Just the main
page content, without the annotations, if any.
page: Page obtained from fz_load_page.
dev: Device obtained from fz_new_*_device.
transform: Transform to apply to page. May include for example
scaling and rotation, see fz_scale, fz_rotate and fz_concat.
Set to fz_identity if no transformation is desired.
cookie: Communication mechanism between caller and library
rendering the page. Intended for multi-threaded applications,
while single-threaded applications set cookie to NULL. The
caller may abort an ongoing rendering of a page. Cookie also
communicates progress information back to the caller. The
fields inside cookie are continually updated while the page is
rendering.
*/
void fz_run_page_contents(fz_context *ctx, fz_page *page, fz_device
*dev, const fz_matrix *transform, fz_cookie *cookie);
/*
fz_run_annot: Run an annotation through a device.
page: Page obtained from fz_load_page.
annot: an annotation.
dev: Device obtained from fz_new_*_device.
transform: Transform to apply to page. May include for example
scaling and rotation, see fz_scale, fz_rotate and fz_concat.
Set to fz_identity if no transformation is desired.
cookie: Communication mechanism between caller and library
rendering the page. Intended for multi-threaded applications,
while single-threaded applications set cookie to NULL. The
CHAPTER 6. THE DOCUMENT INTERFACE 36
caller may abort an ongoing rendering of a page. Cookie also
communicates progress information back to the caller. The
fields inside cookie are continually updated while the page is
rendering.
*/
void fz_run_annot(fz_context *ctx, fz_annot *annot, fz_device *dev,
const fz_matrix *transform, fz_cookie *cookie);
All three of these functions (fz run page, fz run page contents,
fz run annot) take an fz cookie pointer. The Cookie is a lightweight
way of controlling the processing of the page. For more details, see section 7.3
Cookie. For most simple cases this can be NULL.
Chapter 7
The Device interface
7.1 Overview
In many ways, the Device interface is the heart of MuPDF.
When any given document handler is told to run the page (fz run page) the ap-
propriate document interpreter serialises the page contents as a series of graphi-
cal operations, and calls the device interface to perform these actions.
Many different implementations of the device interface exist within MuPDF.
The most obvious one is the Draw device. When this is called, it renders the
graphical objects in turn into a Pixmap.
Alternatively we have the Structured Text device that captures the text out-
put and forms it into an easily processable structure (for searching, or text
extraction).
Some devices, such as the SVG Output device, repackage the graphical objects
into a different format. The end product of these devices is a new document
with (as much as possible) the same overall appearance as the initial page.
Finally, devices such as the Display List device manage to be both implementers
of the interface, and callers of it. Callers can run page contents to the Display
List device just once, and then replay it quickly many times over to other devices;
ideal for rendering pages in bands, or repeatedly redrawing as a viewer pans and
zooms around a document.
By implementing new devices callers can tap the power of MuPDF in new and
interesting ways, perhaps to harness specific hardware facilities of a device.
37
CHAPTER 7. THE DEVICE INTERFACE 38
7.2 Device Methods
Every Device in MuPDF is an extension of the fz device structure. This
contains a series of function pointers to implement the handling of different
types of graphical object.
These function pointers are exposed to callers via convenience functions. These
convenience functions should always be used in preference to calling the
function pointers direct, as they perform various behind the scenes housekeeping
functions. They also cope with the function pointers being NULL, as can permis-
sibly happen when a device is not interested in a particular class of graphical
object.
We describe the convenience functions here; implementers of devices can trivi-
ally extrapolate the behaviour of the function pointers from these descriptions.
For example, the fz fill path function described here is implemented by the
fill path function pointer in the fz device that takes the identical arguments
and has the same return conditions.
7.2.1 Line Art
Line Art is handled by the device functions to plot paths. See section 8.9 Paths
for more information.
void fz_fill_path(fz_context *ctx, fz_device *dev, const fz_path *path,
int even_odd, const fz_matrix *ctm, fz_colorspace *colorspace,
const float *color, float alpha);
void fz_stroke_path(fz_context *ctx, fz_device *dev, const fz_path
*path, const fz_stroke_state *stroke, const fz_matrix *ctm,
fz_colorspace *colorspace, const float *color, float alpha);
void fz_clip_path(fz_context *ctx, fz_device *dev, const fz_path *path,
int even_odd, const fz_matrix *ctm, const fz_rect *scissor);
void fz_clip_stroke_path(fz_context *ctx, fz_device *dev, const fz_path
*path, const fz_stroke_state *stroke, const fz_matrix *ctm, const
fz_rect *scissor);
7.2.2 Text
Text is handled by the device functions to plot text. See section 8.10 Text for
more information.
void fz_fill_text(fz_context *ctx, fz_device *dev, const fz_text *text,
const fz_matrix *ctm, fz_colorspace *colorspace, const float
*color, float alpha);
CHAPTER 7. THE DEVICE INTERFACE 39
void fz_stroke_text(fz_context *ctx, fz_device *dev, const fz_text
*text, const fz_stroke_state *stroke, const fz_matrix *ctm,
fz_colorspace *colorspace, const float *color, float alpha);
void fz_clip_text(fz_context *ctx, fz_device *dev, const fz_text *text,
const fz_matrix *ctm, const fz_rect *scissor);
void fz_clip_stroke_text(fz_context *ctx, fz_device *dev, const fz_text
*text, const fz_stroke_state *stroke, const fz_matrix *ctm, const
fz_rect *scissor);
void fz_ignore_text(fz_context *ctx, fz_device *dev, const fz_text
*text, const fz_matrix *ctm);
The fz clip text and fz clip stroke text functions are used to start a clip.
Subsequent operations will be clipped through the areas delimited by these,
until an fz pop clip is seen. See subsection 7.2.5 Clipping and Masking for
more details.
7.2.3 Images
Images are handled by the device functions to plot images. See section 8.6
Images for more information.
void fz_fill_image(fz_context *ctx, fz_device *dev, fz_image *image,
const fz_matrix *ctm, float alpha);
void fz_fill_image_mask(fz_context *ctx, fz_device *dev, fz_image
*image, const fz_matrix *ctm, fz_colorspace *colorspace, const
float *color, float alpha);
void fz_clip_image_mask(fz_context *ctx, fz_device *dev, fz_image
*image, const fz_matrix *ctm, const fz_rect *scissor);
The fz clip image mask function is used to start a clip. Subsequent operations
will be clipped through the area delimited by this, until an fz pop clip is seen.
See subsection 7.2.5 Clipping and Masking for more details.
7.2.4 Shadings
Shaded areas (such as radial, linear and mesh based shadings) are rendered by
filling a (normally) clipped region with a shade. This is achieved by calling
fz fill shade. See section 8.11 Shadings for more details.
void fz_fill_shade(fz_context *ctx, fz_device *dev, fz_shade *shade,
const fz_matrix *ctm, float alpha);
CHAPTER 7. THE DEVICE INTERFACE 40
7.2.5 Clipping and Masking
Graphical objects can be restricted to a given area using Clipping. The area to
clip to can be specified as paths, text, or images as explained in subsection 7.2.1
Line Art, subsection 7.2.2 Text, and subsection 7.2.3 Images.
Each call to such a function starts a clipping group, which will be terminated
by calling:
void fz_pop_clip(fz_context *ctx, fz_device *dev);
Clipping groups can be nested, allowing complex graphical effects.
A related concept to clipping, is that of masking. Whereas clipping regions
are simple on or off things, where content is chopped off at hard edges, mas-
king allows for regions that allow just some proportion of the content to show
through.
Masking operations take place in 2 stages; first the mask itself is defined, then
the content to be masked.
Stage 1 begins by calling fz begin mask to start a mask definition group. Any
series of graphical operations can now be sent to the device which will combine
together to create the mask.
Stage 1 is terminated and Stage 2 begins by calling fz end mask. This converts
the mask definition into a ‘soft clip’. Any series of graphical operations can now
be sent to the device which will combine together to create the mask contents.
The whole process is then completed by calling fz pop clip. This renders the
mask contents through the soft clip, giving the final results.
void fz_begin_mask(fz_context *ctx, fz_device *dev, const fz_rect *area,
int luminosity, fz_colorspace *colorspace, const float *bc);
void fz_end_mask(fz_context *ctx, fz_device *dev);
7.2.6 Groups and Transparency
Some document formats (such as PDF) offer a rich transparency model that
allows graphical objects to be ’Grouped’ together and imposed upon the page
as if they have a given opacity, using a variety of different blend modes.
MuPDF implements this by using the fz begin group and fz end group calls.
void fz_begin_group(fz_context *ctx, fz_device *dev, const fz_rect
*area, int isolated, int knockout, int blendmode, float alpha);
void fz_end_group(fz_context *ctx, fz_device *dev);
CHAPTER 7. THE DEVICE INTERFACE 41
The exact details of PDF transparency are too complex to explain here; for a
full explanation see The PDF Reference Manual.
7.2.7 Tiling
Many document formats allow for content to be tiled repeatedly. Frequently
this is used to implement patterns for filling other graphical operations.
MuPDF implements this by allowing a group of content to be defined that is
then tiled repeatedly across an area.
The content definition begins by calling fz begin tile id, giving the area of
the page to be filled (area), the area of a single tile (view), the x and y steps
between repeats of the tile (xstep and ystep), the transformation to take all of
these measurements out of pattern space to device space (ctm) and an integer
id.
The purpose of id is to allow for efficient caching of rendered tiles. If id is
0, then no caching is performed. If it is non-zero, then it assumed to uniquely
identify this tile. The tile can be safely placed into the Store (see chapter 5
Reference Counting, Memory Management and The Store) and future uses of
this tile can short circuit the tile definition/rendering phase.
If a tile is found in the store, then fz begin tile id will return non-zero and
the caller can proceed directly to the call to fz end tile.
Any graphical operations sent to the device will be taken as part of the tile
content, until fz end tile is called, whereupon these graphical operations will
be imposed upon the output.
For the convenience of the caller, if no id is available (and hence no caching is
possible), the fz begin tile variant can be used instead.
void fz_begin_tile(fz_context *ctx, fz_device *dev, const fz_rect *area,
const fz_rect *view, float xstep, float ystep, const fz_matrix
*ctm);
int fz_begin_tile_id(fz_context *ctx, fz_device *dev, const fz_rect
*area, const fz_rect *view, float xstep, float ystep, const
fz_matrix *ctm, int id);
void fz_end_tile(fz_context *ctx, fz_device *dev);
7.2.8 Render Flags
Every device has a set of render flags (a simple int, in which bits can be set or
cleared).
CHAPTER 7. THE DEVICE INTERFACE 42
These flags tend to have meanings specific to individual devices. In an ideal
world they would not be required, but having this mechanism here can provide
noticeable quality improvements.
void fz_render_flags(fz_context *ctx, fz_device *dev, int set, int
clear);
The function basically does:
flags = (flags | set) & ~clear;
That is to say, the bits given in set are set, and then the bits given in clear
are cleared.
The current only documented use of this is for the GProof device to request the
Draw device to grid fit its tiled images.
The reason for using Render Flags rather than Device Hints (see section 7.4
Device Hints) is that Render Flags can be carried forward though display lists.
7.3 Cookie
The cookie is a lightweight mechanism for controlling and detecting the beha-
viour of a given interpretation call (i.e. fz run page, fz run page contents,
fz run annot, fz run display list etc).
To use the cookie, a caller should simply define:
fz_cookie *cookie = { 0 };
set any required fields, for example:
cookie.incomplete_ok = 1;
and then pass &cookie as the last parameter to the interpretation call, for
example:
fz_run_page(ctx, page, dev, transform, &cookie);
The contents and definition of fz cookie are even more subject to change than
other structures, so it is important to always initialise all the subfields to zero.
The safest way to do this is as given above. If new fields are added to the
structure, callers code should not need to change, and the default behaviour of
zero-valued new fields will always remain the same.
CHAPTER 7. THE DEVICE INTERFACE 43
7.3.1 Detecting errors
When displaying a page, if we hit an error, what should we do?
We could choose to stop interpretation entirely, but that would mean that a
relatively unimportant error (such as a missing or broken font) would prevent
us getting anything useful out of a page.
We could choose to ignore the errors and continue, but that would be a problem
for (say) a print run, where it would undesirable for us to print 1000 copies of
a document only to discover that it’s missing an image.
The strategy taken by MuPDF is to swallow errors during interpretation, but
keep a count of them in the errors field within the cookie. That way callers can
check that cookie.errors == 0 at the end to know whether a run completed
without incident.
7.3.2 Using the cookie with threads
Content interpretations can take a (relatively) long time. Once one has been
started, it can be useful a) to know how far through processing we are, and b)
to be able to abort processing should the results of a run no longer be required.
As a run progresses, 2 fields in the cookie are updated. Firstly, progress will
be set to a number that increases as progress is made. Think of this informally
as being the number of objects that have been processed so far. In some cases
(notably when processing a display list) we can know an upper bound for this
value, and this value will be given as progress max. In cases where no upper
bound is known, progress max will be set to -1. It is possible that the upper
bound may start as -1, and then change to a known value later.
These values are intended to enable user feedback to be given, and should not
be taken as guarantees of performance.
While running content, the interpreter periodically checks the abort field of the
cookie. If it is discovered to be non zero, the rest of the content is ignored.
If the caller decides that it does not need the results of a run once it has been
started (perhaps the user changes the page, or closes the file), then it should
therefore set the abort field of the cookie to 1.
No guarantees are made about how often the cookie is checked, nor about how
fast an interpreter will respond to the abort field once it is set. Setting the abort
flag will never hurt, and will frequently help, however. Once the flag has been
set to 1, it should never be reset to 0, as the results will be unpredictable.
Resources used by a run cannot be released until the end of a run, regardless of
the setting of abort. Callers still need to wait for the fz run page (or other)
call to complete before the page etc can be safely dropped.
CHAPTER 7. THE DEVICE INTERFACE 44
7.3.3 Using the cookie to control partial rendering
The cookie also has a role to play when working in Progressive Mode. The
incomplete ok and incomplete fields are used for this. See chapter 16 Pro-
gressive Mode) for more details.
7.4 Device Hints
Device Hints are a mechanism that enables control over the behaviour of a
device, and to interpreters calling to that device. Informally they offer hints
about what a device is going to do and therefore what callers need to worry
about.
Device hints take the form of bits in an int that can be enabled (set) or disabled
(cleared). Callers can query these hints to customise their behaviour.
/*
fz_enable_device_hints : Enable hints in a device.
hints: mask of hints to enable.
For example: By default the draw device renders shadings. For some
purposes (perhaps rendering fast low quality thumbnails) you may want
to tell it to ignore shadings. For this you would enable the
FZ_IGNORE_SHADE hint.
*/
void fz_enable_device_hints(fz_context *ctx, fz_device *dev, int hints);
/*
fz_disable_device_hints : Disable hints in a device.
hints: mask of hints to disable.
For example: By default the text extraction device ignores images.
For some purposes however (such as extracting HTML) you may want to
enable the capturing of image data too. For this you would disable
the FZ_IGNORE_IMAGE hint.
*/
void fz_disable_device_hints(fz_context *ctx, fz_device *dev, int hints);
Some devices set the hints to non-zero default values.
For example, when running a text-extraction operation (as used to implement
text search), there is little point in handling images, or shadings. The text
extraction device therefore sets FZ IGNORE IMAGE and FZ IGNORE SHADE. The
interpretation functions (such as fz run page or fz run display list can then
not bother to prepare images for calling into the device, improving performance.
CHAPTER 7. THE DEVICE INTERFACE 45
If, however, you wish to extract the page content to an html file, you might
want to include images in this output. So for this, you would disable the
FZ IGNORE IMAGE hint before running the extraction, and the text extraction
device would know to include them in its output structures.
The set of hints is subject to expansion in future, but is currently defined to be:
enum
{
/* Hints */
FZ_IGNORE_IMAGE = 1,
FZ_IGNORE_SHADE = 2,
FZ_DONT_INTERPOLATE_IMAGES = 4,
FZ_MAINTAIN_CONTAINER_STACK = 8,
FZ_NO_CACHE = 16,
};
FZ IGNORE IMAGE being enabled implies that a device will (or should) make no
effort to handle images. For example, when playing back a display list (with
fz run display list), if the target device sets FZ IGNORE IMAGE, no image
related calls will be made.
FZ IGNORE SHADE being enabled implies that a device will (or should) make no
effort to handle shadings. For instance, if you are doing a quick pass across files
trying to generate low quality thumbnail images, you may choose to disable
shadings for speed.
FZ DONT INTERPOLAGE IMAGES being enabled prevents the draw device perfor-
ming interpolation. MuTool Draw uses this to inhibit interpolation when anti-
aliasing is disabled. Finer control over this can now be given using the Tuning
Context (see section 3.7 Tuning).
FZ MAINTAIN CONTAINER STACK being enabled helps devices by causing MuPDF
to maintain a stack of containers. This effectively moves some logic that would
have to be in several devices into a place where it can be easily reused. Currently
the only device that makes use of this is the SVG device, but it is hoped that
more will use it in future.
FZ NO CACHE being enabled tells the interpreter to try to avoid caching any
objects after the end of the content run. This can be used, for example, when
searching a PDF for a text string to avoid pulling all the images, shadings, fonts
etc and other resources for pages into memory at the expense of those that are
used on the current page.
CHAPTER 7. THE DEVICE INTERFACE 46
7.5 Inbuilt Devices
MuPDF comes with a selection of devices built in, though this should not be
taken as a definitive list. It is expected that other devices will be written to
extend MuPDF - indeed some embeddings of MuPDF already include their own
devices.
7.5.1 BBox Device
The BBox device is a simple device that calculates the bbox of all the marking
operations on a page.
/*
fz_new_bbox_device: Create a device to compute the bounding
box of all marks on a page.
The returned bounding box will be the union of all bounding
boxes of all objects on a page.
*/
fz_device *fz_new_bbox_device(fz_context *ctx, fz_rect *rectp);
The fz rect passed to the fz new bbox device must obviously stay in scope
for the duration of the life of the device as it will be updated on exit with the
bounding box for the contents.
7.5.2 Draw Device
The Draw device is the core renderer for MuPDF. Every draw device instance
is constructed with a destination Pixmap (see section 8.3 Pixmaps for more
details), and each graphical object passed to the device is rendered into that
pixmap.
/*
fz_new_draw_device: Create a device to draw on a pixmap.
dest: Target pixmap for the draw device. See fz_new_pixmap*
for how to obtain a pixmap. The pixmap is not cleared by the
draw device, see fz_clear_pixmap* for how to clear it prior to
calling fz_new_draw_device. Free the device by calling
fz_drop_device.
*/
fz_device *fz_new_draw_device(fz_context *ctx, fz_pixmap *dest);
Most of the time we render complete pixmaps, but a mechanism exists to allow
us to render a given bbox within a pixmap:
CHAPTER 7. THE DEVICE INTERFACE 47
/*
fz_new_draw_device_with_bbox: Create a device to draw on a pixmap.
dest: Target pixmap for the draw device. See fz_new_pixmap*
for how to obtain a pixmap. The pixmap is not cleared by the
draw device, see fz_clear_pixmap* for how to clear it prior to
calling fz_new_draw_device. Free the device by calling
fz_drop_device.
clip: Bounding box to restrict any marking operations of the
draw device.
*/
fz_device *fz_new_draw_device_with_bbox(fz_context *ctx, fz_pixmap
*dest, const fz_irect *clip);
This can be useful for updating particular areas of a page (for instance when an
annotation has been edited or moved) without redrawing the whole thing.
During the course of rendering, the draw device may create new temporary
internal pixmaps to cope with transparency and grouping. This is invisible to
the caller, and can safely be considered an implementation detail, but should
be considered when estimating the memory use for a given rendering operation.
The exact number and size of internal pixmaps required depends on the exact
complexity and makeup of the graphical objects being displayed.
To limit memory use, a typical strategy is to render pages in bands; rather than
creating a single pixmap the size of the page and rendering that, create pixmaps
for ’slices’ across the page, and render them one at a time. The memory savings
are not just seen in the cost of the basic pixmap, but also serve to limit the sizes
of the internal pixmaps used during rendering.
The cost for this is that the page contents do need to be run through repeatedly.
This can be achieved by reinterpreting directly from the file, but that can be
expensive. The next device provides a route to help with this.
7.5.3 Display List Device
The Display list device simply records all the calls made to it in a list. This
list can then be played back later, potentially multiple times and with different
transforms, to other devices.
/*
fz_new_list_device: Create a rendering device for a display list.
When the device is rendering a page it will populate the
display list with drawing commsnds (text, images, etc.). The
display list can later be reused to render a page many times
without having to re-interpret the page from the document file
CHAPTER 7. THE DEVICE INTERFACE 48
for each rendering. Once the device is no longer needed, free
it with fz_drop_device.
list: A display list that the list device takes ownership of.
*/
fz_device *fz_new_list_device(fz_context *ctx, fz_display_list *list);
For more details of the uses of Display Lists, see chapter 9 Display Lists.
7.5.4 PDF Output Device
The PDF Output device is still a work in progress, as its handling of fonts is
incomplete. Nonetheless for certain classes of files it can be useful.
End users will probably prefer to use the document writer interface (see /rj-
wrefDocumentWriter) which wraps this class up, rather than call it directly.
Nonetheless this can be useful in specific circumstances when generating parti-
cular sections of a PDF file (such as appearance streams for annotations).
The PDF Output device takes the sequence of graphical operations it is called
with, and forms it back into a sequence of PDF operations, together with a set
of required resources. These can then be formed into a completely new PDF
page (or a PDF annotation) which can then be inserted into a document.
/*
pdf_page_write: Create a device that will record the
graphical operations given to it into a sequence of
pdf operations, together with a set of resources. This
sequence/set pair can then be used as the basis for
adding a page to the document (see pdf_add_page).
doc: The document for which these are intended.
mediabox: The bbox for the created page.
presources: Pointer to a place to put the created
resources dictionary.
pcontents: Pointer to a place to put the created
contents buffer.
*/
fz_device *pdf_page_write(fz_context *ctx, pdf_document *doc, const
fz_rect *mediabox, pdf_obj **presources, fz_buffer **pcontents);
For more information about page manipulation in PDF documents, see chap-
ter 19 PDF Page Manipulation.
CHAPTER 7. THE DEVICE INTERFACE 49
7.5.5 Structured Text Device
The Structured Text device is used to extract the text from a given graphical
stream, together with the position it inhabits on the output page. It can also
optionally include details of images and their positions within its output.
/*
fz_new_stext_device: Create a device to extract the text on a page.
Gather and sort the text on a page into spans of uniform style,
arranged into lines and blocks by reading order. The reading order
is determined by various heuristics, so may not be accurate.
sheet: The text sheet to which styles should be added. This can
either be a newly created (empty) text sheet, or one containing
styles from a previous text device. The same sheet cannot be used
in multiple threads simultaneously.
page: The text page to which content should be added. This will
usually be a newly created (empty) text page, but it can be one
containing data already (for example when merging multiple pages, or
watermarking).
*/
fz_device *fz_new_stext_device(fz_context *ctx, fz_stext_sheet *sheet,
fz_stext_page *page);
This can be used as the basis for searching (including highlighting the text as
matches are found), for exporting text files (or text and image based files such
as HTML), or even to do more complex page analysis (such as spotting what
regions of the page are text, what are graphics etc).
An (initially empty) fz stext sheet should be created using
fz new stext sheet, and an empty fz stext page created using
fz new stext page. These are used in the call to fz new stext device.
After the contents have been run to that device, the sheet will be populated
with the common styles used by the page, and the page will be populated with
details of the text extracted and its position.
7.5.6 SVG Output Device
The SVG output device is used to generate SVG pages from arbitrary input.
End users will probably prefer to use the document writer interface (see /rj-
wrefDocumentWriter) which wraps this class up, rather than call it directly.
/*
fz_new_svg_device: Create a device that outputs (single page)
SVG files to the given output stream.
CHAPTER 7. THE DEVICE INTERFACE 50
output: The output stream to send the constructed SVG page
to.
page_width, page_height: The page dimensions to use (in
points).
*/
fz_device *fz_new_svg_device(fz_context *ctx, fz_output *out, float
page_width, float page_height);
The device currently generates SVG 1.1 compliant files. SVG Fonts are NOT
used due to poor client support. Instead glyphs are sent as reusable symbols.
Shadings are sent as rasterised images. JPEGs will be passed through unchan-
ged, and all other images will be converted to PNG.
7.5.7 Test Device
The Test device, as its name suggests, tests a given set of page contents for
which features are used. Currently this is restricted to testing for whether the
graphical objects used are greyscale or colour. Testing for additional features
may be added in future.
/*
fz_new_test_device: Create a device to test for features.
Currently only tests for the presence of non-grayscale colors.
is_color: Possible values returned:
0: Definitely greyscale
1: Probably color (all colors were grey, but there
were images or shadings in a non grey colorspace).
2: Definitely color
threshold: The difference from grayscale that will be tolerated.
Typical values to use are either 0 (be exact) and 0.02 (allow an
imperceptible amount of slop).
options: A set of bitfield options, from the FZ_TEST_OPT set.
passthrough: A device to pass all calls through to, or NULL.
If set, then the test device can both test and pass through to
an underlying device (like, say, the display list device). This
means that a display list can be created and at the end we’ll
know if its color or not.
In the absence of a passthrough device, the device will throw
an exception to stop page interpretation when color is found.
*/
CHAPTER 7. THE DEVICE INTERFACE 51
fz_device *fz_new_test_device(fz_context *ctx, int *is_color, float
threshold, int options, fz_device *passthrough);
The expected purpose of the colour detecting functionality is to allow applica-
tions (e.g. printers) to easily detect if a given page requires the use of colour
inks, or whether a greyscale rendering will suffice.
This device can either be used by itself, or in the form of a pass-through device.
Standalone use
In the simplest form, the device can be created standalone, by passing
passthrough as NULL.
As each subsequent device call is made, the device will test the graphic object
passed to it to see if it is within the given threshold of being a neutral colour.
If it is, then the device continues. If not, then it sets the int pointed to by
is color to be non zero.
For graphical objects such as paths or text, this is an easy evaluation that takes
almost no time. For Images or Shadings however, it is slightly trickier. An
image may be defined in a colour space capable of non-neutral colours (perhaps
RGB or CMYK) and yet the image itself may only use neutral colours within
that space. To properly establish whether colours are required or not, requires
much more CPU intensive processing.
Accordingly, the device will, by default, just look at the colour space. The value
of is color returned at the end may be examined to establish the confidence
level of the test. 0 means “definitely greyscale”, 1 means “probably colour” (i.e.
“an image or shading was seen that potentially contains non neutral colours”),
and 2 means “definitely colour”.
If the caller wishes to spend the CPU cycles to get a definite answer, options
can be set to FZ TEXT OPT IMAGES | FZ TEXT OPT SHADINGS and images and
shadings will be exhaustively checked.
As an optimisation, given how much faster is is to check non-images and
shadings, it can be worth running the device once without the options set,
and then only running it again with them set if required.
If the device is run with passthrough as NULL, then as soon as it encounters
a “definite” non-neutral colour, it will throw a FZ ABORT error.
Passthrough use
As discussed above, the envisaged use case for this device is to detect whet-
her page contents require colour or not to allow printers to decide whether to
rasterise for colour inks or a faster/cheaper greyscale pass.
CHAPTER 7. THE DEVICE INTERFACE 52
Such printers will normally be operating in banded mode, which requires (or
at least greatly benefits from) the use of a display list. By using the device in
passthrough mode, the testing can be performed at the same time as the list
is built.
Simply create the display list device as you would normally, and pass it into
fz new test device as passthrough. Then run the page contents through
the returned test device. The test device will pass each call through to the
underlying list device and so the display list be built as normal.
When run in this mode, the device can no longer use the ‘early-exit’ optimisation
of throwing a FZ ABORT error.
7.5.8 Trace Device
The Trace device is a simple debugging device that allows an XML-like repre-
sentation of the device calls made to be output.
/*
fz_new_trace_device: Create a device to print a debug trace of all
device calls.
*/
fz_device *fz_new_trace_device(fz_context *ctx, fz_output *out);
This is a useful tool to visualise the contents of display lists.
Chapter 8
Building Blocks
8.1 Overview
MuPDF uses many constructs and concepts that, while not deserving of chapters
in their own rights, do deserve mention.
8.2 Colorspaces
In order to represent a given color for a graphical object, we need both the
color component values and details of the colorspace that the color is specified
in. Color values are defined simply as floats (between 0 and 1 inclusive), and
colorspaces are defined using the fz colorspace structure.
As with many other such structures in MuPDF, these are reference counted
objects (see section 5.2 Reference Counting).
8.2.1 Basic Colorspaces
MuPDF contains a set of inbuilt colorspaces that cover most simple require-
ments. These can
53
CHAPTER 8. BUILDING BLOCKS 54
8.3 Pixmaps
8.3.1 Overview
The fz pixmap structure is used to represent a 2 dimensional array of contone
pixels. This is used throughout MuPDF, as the target of rendering from the
draw device, as internal buffers during processing, and during image decoding.
A pixmap can have an arbitrary number of colour components, together with an
optional alpha plane. Every component sample is represented by an unsigned
char.
The number of colour components corresponds to the colour space of a pixmap;
pixmaps without a colour space must contain no colour planes, just a single
alpha plane.
The data within a pixmap is always stored packed in ‘chunky’ format. For
instance, an RGB pixmap would have data in the form: RGBRGBRGBRGB...
Alpha data is always sent as the last byte in the set corresponding to a pixel.
An RGB pixmap with an alpha plane would be therefore have data of the form:
RGBARGBARGBA...
To allow pixmaps to sensibly ‘subset’ one another, pixmaps have a ‘stride’ field.
This gives the number of bytes difference from the address of the start of the
representation of a pixel to the address of the start of the representation of the
same pixel on the scanline below.
Normally you’d expect stride to be the same as width multiplied by the number
of components in the image (including alpha), but for ‘sub areas’ of larger
pixmaps this can be much larger.
Pixmaps can frequently map onto operating system specific bitmap represen-
tations, but these sometimes require each scanline to be word aligned - again
the provision of stride allows for this. Bottom up bitmaps can be implemented
using a negative stride.
8.3.2 Saving
Various functions exist to either save pixmaps to files, or to (more generally)
write them to fz output streams.
In general, these functions fall into 3 categories of increasing complexity.
Firstly, functions of the form fz save pixmap to ... take a pixmap and write it
to a given filename in the local filesystem.
Secondly, functions of the form fz write pixmap to ... take a pixmap and
write it to a given fz output. The use of an fz output allows for writing to
CHAPTER 8. BUILDING BLOCKS 55
memory buffers, or even potentially to encrypt or compress further as the write
progresses.
Finally, we have an fz band writer class, that allows images to be written to
file in ‘bands’, thus minimising the amount of memory required at any one time.
Typically a band writer is created using a call such as fz new png band writer:
/*
fz_new_png_band_writer: Obtain a fz_band_writer instance
for producing PNG output.
*/
fz_band_writer *fz_new_png_band_writer(fz_context *ctx, fz_output *out);
First, an image header is written, using this writer:
/*
fz_write_header: Cause a band writer to write the header for
a banded image with the given properties/dimensions etc. This
also configures the bandwriter for the format of the data to be
passed in future calls.
w, h: Width and Height of the entire page.
n: Number of components (including alphas).
alpha: Number of alpha components.
xres, yres: X and Y resolutions in dpi.
pagenum: Page number
Throws exception if incompatible data format.
*/
void fz_write_header(fz_context *ctx, fz_band_writer *writer, int w, int
h, int n, int alpha, int xres, int yres, int pagenum);
This has the effect of setting the size and format of the data for the complete
image. The caller then proceeds to render the page in horizontal strips from the
top to the bottom, and pass them in to fz write band:
/*
fz_write_band: Cause a band writer to write the next band
of data for an image.
stride: The byte offset from the first byte of the data
for a pixel to the first byte of the data for the same pixel
on the row below.
band_height: The number of lines in this band.
CHAPTER 8. BUILDING BLOCKS 56
samples: Pointer to first byte of the data.
*/
void fz_write_band(fz_context *ctx, fz_band_writer *writer, int stride,
int band_height, const unsigned char *samples);
The band writer keeps track of how much data has been written, and when an
entire page has been sent, it writes out any image trailer required.
For formats that can accommodate multiple pages, a new call to
fz write header will start the process again. Otherwise (or after the final
image), the band writer can be neatly discarded by calling:
void fz_drop_band_writer(fz_context *ctx, fz_band_writer *writer);
8.4 Bitmaps
The fz bitmap structure is used to represent a 2 dimensional array of mono-
chrome pixels. They are the 1 bit per component equivalent of the fz pixmap
structure.
The core rendering engine of MuPDF does not currently make use of
fz bitmaps, but rather they are used as a step along the way for outputting
rendered information.
Functions exist within MuPDF to create fz bitmaps from fz pixmaps by half-
toning. See section 8.5 Halftones.
/*
fz_new_bitmap_from_pixmap: Make a bitmap from a pixmap and a
halftone.
pix: The pixmap to generate from. Currently must be a single color
component + alpha (where the alpha is assumed to be solid).
ht: The halftone to use. NULL implies the default halftone.
Returns the resultant bitmap. Throws exceptions in the case of
failure to allocate.
*/
fz_bitmap *fz_new_bitmap_from_pixmap(fz_context *ctx, fz_pixmap *pix,
fz_halftone *ht);
fz_bitmap *fz_new_bitmap_from_pixmap_band(fz_context *ctx, fz_pixmap
*pix, fz_halftone *ht, int band_start, int bandheight);
CHAPTER 8. BUILDING BLOCKS 57
Both functions work by applying a fz halftone to the contone values to make
the bitmap. The latter function is a more general version of the former, that
allows for correct operation when rendering in bands - namely that the correct
offset into the halftone table is used.
The data for each Bitmap is packed into bytes most significant bit first. Multiple
components are packed into the same byte, so a CMYK pixmap converted to a
bitmap would have 2 pixels worth of data in the first byte, CMYKCMYK, with
the first pixel in the highest nibble.
The usual reference counting behaviour applies to fz bitmaps, with
fz keep bitmap and fz drop bitmap claiming and releasing references respecti-
vely.
8.5 Halftones
The fz halftone structure represents a set of tiles, one per component, each of a
potentially different size. Each of these tiles is a 2-dimensional array of threshold
values (actually implemented as a single component fz pixmap). During the
halftoning (bitmap creation) process, if the contone value is smaller than the
threshold value, then it remains unset in the output. If it is larger or equal then
it is set in the output.
For convenience, a NULL pointer can be used to signify the default halftone. The
default halftone can also be fetched by using:
/*
fz_default_halftone: Create a ’default’ halftone structure
for the given number of components.
num_comps: The number of components to use.
Returns a simple default halftone. The default halftone uses
the same halftone tile for each plane, which may not be ideal
for all purposes.
*/
fz_halftone *fz_default_halftone(fz_context *ctx, int num_comps);
The creation of halftones is a specialised field upon which much research has
been done. The mechanisms in MuPDF are designed to allow people the freedom
to create and tune the halftones for their particular application.
The usual reference counting behaviour applies to fz halftones, with
fz keep halftone and fz drop halftone claiming and releasing references re-
spectively.
CHAPTER 8. BUILDING BLOCKS 58
8.6 Images
The fz image structure is used to represent a generic Image object in MuPDF.
It can be viewed as an encapsulation from which both a rendering of an image
(as an fz pixmap) and (often) the original source data can be retrieved.
The primary use of an fz image is to allow a rendered pixmap to be retrieved.
This is done by calling:
/*
fz_get_pixmap_from_image: Called to get a handle to a pixmap from
an image.
image: The image to retrieve a pixmap from.
subarea: The subarea of the image that we actually care about (or
NULL to indicate the whole image).
trans: Optional, unless subarea is given. If given, then on entry
this is the transform that will be applied to the complete image.
It should be updated on exit to the transform to apply to the given
subarea of the image. This is used to calculate the desired
width/height for subsampling.
w: If non-NULL, a pointer to an int to be updated on exit to the
width (in pixels) that the scaled output will cover.
h: If non-NULL, a pointer to an int to be updated on exit to the
height (in pixels) that the scaled output will cover.
Returns a non NULL pixmap pointer. May throw exceptions.
*/
fz_pixmap *fz_get_pixmap_from_image(fz_context *ctx, fz_image *image,
const fz_irect *subarea, fz_matrix *trans, int *w, int *h);
Frequently this will involve decoding the image from its source data, so should
be considered a potentially expensive call, both in terms of CPU time, and
memory usage.
To minimise the impact of such decodes, fz images make use of the Store (see
chapter 5 Reference Counting, Memory Management and The Store) to cache
decoded versions in. This means that (subject to enough memory being availa-
ble) repeated calls to get a fz pixmap from the same fz image (with the same
parameters) will return the same fz pixmap each time, with no further decode
being required.
The usual reference counting behaviour applies to fz images, with
fz keep image and fz drop image claiming and releasing references respecti-
vely.
CHAPTER 8. BUILDING BLOCKS 59
Depending on the size at which an fz image is to be used, it may not be worth
decoding it at full resolution; instead, decoding it at a smaller size can save
memory (and frequently time). In addition, subsequent rendering operations
can often be faster due to having to handle fewer pixels for no quality loss in
the final output.
To facilitate this, fz images will subsample images as appropriate. Subsampling
involves an image being decoded to a size an integer power of 2 smaller than
their native size. For instance, if an image has a native size of 400x300, and is to
be rendered to a final size of 40x30, fz get pixmap from image may subsample
the returned image by up to 8 in each direction, resulting in a 50x37 image.
Subsequent operations (such as smooth scaling and rendering) will proceed much
faster due to fewer pixels being involved, and around one sixteenth of the me-
mory will be required.
Various different implementations of fz image exist within MuPDF.
8.6.1 Compressed Images
The fz
compressed image structure is a specialisation of fz image, that holds
the source data for an image in an fz compressed buffer. This is the usual
form for images created from PDF and XPS files.
The data for a compressed image can be retrieved by calling:
fz_compressed_buffer *fz_compressed_image_buffer(fz_context *ctx,
fz_image *image);
If the supplied fz image is not an fz compressed image then it will return
NULL.
8.6.2 Pixmap Images
The fz pixmap image structure is a specialisation of fz image, that has an
fz pixmap as its source data. This exists to allow fz pixmaps from other sources
to be easily fed into the MuPDF rendering engine.
8.7 Buffers
The fz buffer structure is used to represent arbitrary buffers of data. Es-
sentially they are a representation for arbitrary blocks of bytes (in whatever
encoding required), with simple functions for extending, concatenating, and
writing in byte, char, utf8 and bitwise fashion.
CHAPTER 8. BUILDING BLOCKS 60
Both the internals and API level functions of MuPDF use fz buffers extensi-
vely.
The usual reference counting behaviour applies to fz buffers, with
fz keep buffer and fz drop buffer claiming and releasing references respecti-
vely.
8.8 Transforms
The fz matrix structure is used to represent 2 dimensional matrices used for
transforming points, shapes and other geometry.
The six fields of the fz matrix structure correspond to a matrix of the form:
a b 0
c d 0
e f 1
Such transformation matrices can be used to represent a wide range of different
operations, including translations, rotations, scales, sheers, and any combination
thereof.
Typically, a matrix will be created for a specific purpose, such as a scale, or a
translation. For this reason, we have dedicated construction calls.
/*
fz_scale: Create a scaling matrix.
The returned matrix is of the form [ sx 0 0 sy 0 0 ].
m: Pointer to the matrix to populate
sx, sy: Scaling factors along the X- and Y-axes. A scaling
factor of 1.0 will not cause any scaling along the relevant
axis.
Returns m.
Does not throw exceptions.
*/
fz_matrix *fz_scale(fz_matrix *m, float sx, float sy);
/*
fz_shear: Create a shearing matrix.
The returned matrix is of the form [ 1 sy sx 1 0 0 ].
CHAPTER 8. BUILDING BLOCKS 61
m: pointer to place to store returned matrix
sx, sy: Shearing factors. A shearing factor of 0.0 will not
cause any shearing along the relevant axis.
Returns m.
Does not throw exceptions.
*/
fz_matrix *fz_shear(fz_matrix *m, float sx, float sy);
/*
fz_rotate: Create a rotation matrix.
The returned matrix is of the form
[ cos(deg) sin(deg) -sin(deg) cos(deg) 0 0 ].
m: Pointer to place to store matrix
degrees: Degrees of counter clockwise rotation. Values less
than zero and greater than 360 are handled as expected.
Returns m.
Does not throw exceptions.
*/
fz_matrix *fz_rotate(fz_matrix *m, float degrees);
/*
fz_translate: Create a translation matrix.
The returned matrix is of the form [ 1 0 0 1 tx ty ].
m: A place to store the created matrix.
tx, ty: Translation distances along the X- and Y-axes. A
translation of 0 will not cause any translation along the
relevant axis.
Returns m.
Does not throw exceptions.
*/
fz_matrix *fz_translate(fz_matrix *m, float tx, float ty);
Mathematically, points are transformed by multiplying them (extended to 3
elements long). For example (x’,y’), the point given by mapping (x,y) through
such a matrix is calculated as follows:
CHAPTER 8. BUILDING BLOCKS 62
x
0
y
0
1
=
x y 1
a b 0
c d 0
e f 1
There are various functions in MuPDF to perform such transformations:
/*
fz_transform_point: Apply a transformation to a point.
transform: Transformation matrix to apply. See fz_concat,
fz_scale, fz_rotate and fz_translate for how to create a
matrix.
point: Pointer to point to update.
Returns transform (unchanged).
Does not throw exceptions.
*/
fz_point *fz_transform_point(fz_point *restrict point, const fz_matrix
*restrict transform);
fz_point *fz_transform_point_xy(fz_point *restrict point, const
fz_matrix *restrict transform, float x, float y);
Rectangles can be transformed using the following function, which allows for
the fact that the image of a rectangle may be flipped:
/*
fz_transform_rect: Apply a transform to a rectangle.
After the four corner points of the axis-aligned rectangle
have been transformed it may not longer be axis-aligned. So a
new axis-aligned rectangle is created covering at least the
area of the transformed rectangle.
transform: Transformation matrix to apply. See fz_concat,
fz_scale and fz_rotate for how to create a matrix.
rect: Rectangle to be transformed. The two special cases
fz_empty_rect and fz_infinite_rect, may be used but are
returned unchanged as expected.
Does not throw exceptions.
*/
fz_rect *fz_transform_rect(fz_rect *restrict rect, const fz_matrix
*restrict transform);
CHAPTER 8. BUILDING BLOCKS 63
Also, it can be useful to transform a point, ignoring the translation components
of a transformation, so we have a convenience function for this:
/*
fz_transform_vector: Apply a transformation to a vector.
transform: Transformation matrix to apply. See fz_concat,
fz_scale and fz_rotate for how to create a matrix. Any
translation will be ignored.
vector: Pointer to vector to update.
Does not throw exceptions.
*/
fz_point *fz_transform_vector(fz_point *restrict vector, const fz_matrix
*restrict transform);
Transformations can be combined by multiplying their representative matrices
together. Transforming a point by applying matrix A then matrix B, will give
identical results to transforming the point by AB.
MuPDF provides an API for combining matrices in this way:
/*
fz_concat: Multiply two matrices.
The order of the two matrices are important since matrix
multiplication is not commutative.
Returns result.
Does not throw exceptions.
*/
fz_matrix *fz_concat(fz_matrix *result, const fz_matrix *left, const
fz_matrix *right);
Alternatively, operations can be specifically applied to existing matrices. Be-
cause of the non-commutative nature of matrix operations, it matters whether
the new operation is applied before or after the existing matrix.
For example, if you have a matrix that performs a rotation, and you wish
to combine that with a translation, you must decide whether you want the
translation to occur before the rotation (‘pre’) or afterwards (‘post’).
MuPDF has various API functions for such operations:
/*
fz_pre_scale: Scale a matrix by premultiplication.
m: Pointer to the matrix to scale
CHAPTER 8. BUILDING BLOCKS 64
sx, sy: Scaling factors along the X- and Y-axes. A scaling
factor of 1.0 will not cause any scaling along the relevant
axis.
Returns m (updated).
Does not throw exceptions.
*/
fz_matrix *fz_pre_scale(fz_matrix *m, float sx, float sy);
/*
fz_post_scale: Scale a matrix by postmultiplication.
m: Pointer to the matrix to scale
sx, sy: Scaling factors along the X- and Y-axes. A scaling
factor of 1.0 will not cause any scaling along the relevant
axis.
Returns m (updated).
Does not throw exceptions.
*/
fz_matrix *fz_post_scale(fz_matrix *m, float sx, float sy);
/*
fz_pre_shear: Premultiply a matrix with a shearing matrix.
The shearing matrix is of the form [ 1 sy sx 1 0 0 ].
m: pointer to matrix to premultiply
sx, sy: Shearing factors. A shearing factor of 0.0 will not
cause any shearing along the relevant axis.
Returns m (updated).
Does not throw exceptions.
*/
fz_matrix *fz_pre_shear(fz_matrix *m, float sx, float sy);
/*
fz_pre_rotate: Rotate a transformation by premultiplying.
The premultiplied matrix is of the form
[ cos(deg) sin(deg) -sin(deg) cos(deg) 0 0 ].
m: Pointer to matrix to premultiply.
CHAPTER 8. BUILDING BLOCKS 65
degrees: Degrees of counter clockwise rotation. Values less
than zero and greater than 360 are handled as expected.
Returns m (updated).
Does not throw exceptions.
*/
fz_matrix *fz_pre_rotate(fz_matrix *m, float degrees);
/*
fz_pre_translate: Translate a matrix by premultiplication.
m: The matrix to translate
tx, ty: Translation distances along the X- and Y-axes. A
translation of 0 will not cause any translation along the
relevant axis.
Returns m.
Does not throw exceptions.
*/
fz_matrix *fz_pre_translate(fz_matrix *m, float tx, float ty);
Finally, sometimes it is useful to find the matrix that would represent the reverse
of a given transformation. This can be achieved by ‘inverting’ the matrix.
This is not possible in all cases, but can be achieved for most ‘well-behaved’
transformations.
/*
fz_invert_matrix: Create an inverse matrix.
inverse: Place to store inverse matrix.
matrix: Matrix to invert. A degenerate matrix, where the
determinant is equal to zero, can not be inverted and the
original matrix is returned instead.
Returns inverse.
Does not throw exceptions.
*/
fz_matrix *fz_invert_matrix(fz_matrix *inverse, const fz_matrix *matrix);
/*
fz_try_invert_matrix: Attempt to create an inverse matrix.
inverse: Place to store inverse matrix.
CHAPTER 8. BUILDING BLOCKS 66
matrix: Matrix to invert. A degenerate matrix, where the
determinant is equal to zero, can not be inverted.
Returns 1 if matrix is degenerate (singular), or 0 otherwise.
Does not throw exceptions.
*/
int fz_try_invert_matrix(fz_matrix *inverse, const fz_matrix *matrix);
8.9 Paths
Postscript (or PDF) style paths are represented using the fz path structure. A
postscript path consists of a sequence of instructions describing the movement
of a ‘pen’ around a given path.
The first instruction is always a ‘move’ to a specified location. Subsequent in-
structions move the pen position onwards to new positions on the page, either
via straight lines, or via curves described by given control points. Such instructi-
ons can either be made with the pen up or down.
Once created paths can then be rendered by MuPDF either by being filled, or
by being stroked. The path itself has no knowledge of how it will be used - the
details of the fill or the stroke attributes are supplied externally to this structure.
A description of the exact rules used for filling and stroking are beyond the scope
of this document. For more information see “The PDF Reference Manual” or
“The Postscript Language Reference Manual”.
Paths are reference counted objects, with the implicit understanding that once
more than one reference exists to a path, it will no longer be modified.
8.9.1 Creation
A reference to a new empty path can be created using fz new path:
/*
fz_new_path: Create an empty path, and return
a reference to it.
Throws exception on failure to allocate.
*/
fz_path *fz_new_path(fz_context *ctx);
Once a path exists, commands can be added to it. The first command must
always be a ‘move’.
CHAPTER 8. BUILDING BLOCKS 67
/*
fz_moveto: Append a ’moveto’ command to a path.
path: The path to modify.
x, y: The coordinate to move to.
Throws exceptions on failure to allocate.
*/
void fz_moveto(fz_context *ctx, fz_path *path, float x, float y);
Once we have moved to a point, subsequent commands can be added, such as
lines, quads (quadratic beziers) and curves (cubic beziers).
/*
fz_lineto: Append a ’lineto’ command to a path.
path: The path to modify.
x, y: The coordinate to line to.
Throws exceptions on failure to allocate.
*/
void fz_lineto(fz_context *ctx, fz_path *path, float x, float y);
/*
fz_quadto: Append a ’quadto’ command to a path. (For a
quadratic bezier).
path: The path to modify.
x0, y0: The control coordinates for the quadratic curve.
x1, y1: The end coordinates for the quadratic curve.
Throws exceptions on failure to allocate.
*/
void fz_quadto(fz_context *ctx, fz_path *path, float x0, float y0, float
x1, float y1);
/*
fz_curveto: Append a ’curveto’ command to a path. (For a
cubic bezier).
path: The path to modify.
x0, y0: The coordinates of the first control point for the
curve.
CHAPTER 8. BUILDING BLOCKS 68
x1, y1: The coordinates of the second control point for the
curve.
x2, y2: The end coordinates for the curve.
Throws exceptions on failure to allocate.
*/
void fz_curveto(fz_context *ctx, fz_path *path, float x0, float y0,
float x1, float y1, float x2, float y2);
In addition, we have 2 functions for adding curves (cubic beziers) where one
of the control points is coincident with the neighbouring endpoints. These
functions mirror the usage in PDF, but offer no benefits other than convenience
as such curves are detected automatically as part of an fz curveto call.
/*
fz_curvetov: Append a ’curvetov’ command to a path. (For a
cubic bezier with the first control coordinate equal to
the start point).
path: The path to modify.
x1, y1: The coordinates of the second control point for the
curve.
x2, y2: The end coordinates for the curve.
Throws exceptions on failure to allocate.
*/
void fz_curvetov(fz_context *ctx, fz_path *path, float x1, float y1,
float x2, float y2);
/*
fz_curvetoy: Append a ’curvetoy’ command to a path. (For a
cubic bezier with the second control coordinate equal to
the end point).
path: The path to modify.
x0, y0: The coordinates of the first control point for the
curve.
x2, y2: The end coordinates for the curve (and the second
control coordinate).
Throws exceptions on failure to allocate.
*/
void fz_curvetoy(fz_context *ctx, fz_path *path, float x0, float y0,
float x2, float y2);
CHAPTER 8. BUILDING BLOCKS 69
At any point after the initial move, we can close the path using fz closepath:
/*
fz_closepath: Close the current subpath.
path: The path to modify.
Throws exceptions on failure to allocate, and illegal
path closes.
*/
void fz_closepath(fz_context *ctx, fz_path *path);
After a path has been closed, the only acceptable next command is a move. A
path need not be closed before a second or subsequent move is sent.
Finally, we have one additional path construction function, fz rectto. This
appends a rectangle to the current path. This rectangle is equivalent to a move,
3 lines and a closepath, and so is the one exception to the rule that paths must
begin with a move (as one is implicit within the rectangle command).
/*
fz_rectto: Append a ’rectto’ command to a path.
The rectangle is equivalent to:
moveto x0 y0
lineto x1 y0
lineto x1 y1
lineto x0 y1
closepath
path: The path to modify.
x0, y0: First corner of the rectangle.
x1, y1: Second corner of the rectangle.
Throws exceptions on failure to allocate.
*/
void fz_rectto(fz_context *ctx, fz_path *path, float x0, float y0, float
x1, float y1);
Finally, during path construction, the coordinate at which the notional path
cursor has reached can be read using the fz currentpoint function.
/*
fz_currentpoint: Return the current point that a path has
reached or (0,0) if empty.
path: path to return the current point of.
CHAPTER 8. BUILDING BLOCKS 70
*/
fz_point fz_currentpoint(fz_context *ctx, fz_path *path);
8.9.2 Reference counting
As stated before, fz paths are reference counted objects. Once one has been
created, references can be created/destroyed using the standard keep/drop con-
ventions:
/*
fz_keep_path: Take an additional reference to
a path.
No modifications should be carried out on a path
to which more than one reference is held, as
this can cause race conditions.
Never throws exceptions.
*/
fz_path *fz_keep_path(fz_context *ctx, const fz_path *path);
/*
fz_drop_path: Drop a reference to a path,
destroying the path if it is the last
reference.
Never throws exceptions.
*/
void fz_drop_path(fz_context *ctx, const fz_path *path);
A path with more than one reference is considered to be ‘frozen’ or ‘immutable’.
It is not safe to modify such a path, as the other holder of a reference to it may
not expect it to be being changed. That is to say that modification operations
on paths are not atomic between threads.
If you have a path that you wish to be able to modify, simply call fz clone path
to obtain a reference to a copy of the path that is safe to modify:
/*
fz_clone_path: Clone the data for a path.
This is used in preference to fz_keep_path when a whole
new copy of a path is required, rather than just a shared
pointer. This probably indicates that the path is about to
be modified.
path: path to clone.
CHAPTER 8. BUILDING BLOCKS 71
Throws exceptions on failure to allocate.
*/
fz_path *fz_clone_path(fz_context *ctx, fz_path *path);
8.9.3 Storage
Because Paths are such a crucial part of MuPDF, and are used so widely in
document content, we take particular care to allow them to be expressed and
accessed efficiently.
This means that at path construction time, we spot simple cases where we can
optimise the path representation. For example, a move immediately following
a move can cause the first move to be dropped. Similarly, a curve with both
control points coincident with the endpoints can be expressed as a line.
This means that if you read a path out after construction (see subsection 8.9.7
Walking) you cannot rely on the exact representation being the same.
In addition, after constructing a path, there are some simple things that can be
done to minimise the memory used.
As paths are constructed, the data buffers within them grow. For efficiency,
these grow with some slack in them, so at the end of construction there can be
a non-trivial amount of space wasted.
If you intend to simply use the path, and then discard it, this does not matter.
If instead you intend to keep the path around for a while, it may be worth
calling fz trim path to shrink the storage buffers as much as possible.
/*
fz_trim_path: Minimise the internal storage
used by a path.
As paths are constructed, the internal buffers
grow. To avoid repeated reallocations they
grow with some spare space. Once a path has
been fully constructed, this call allows the
excess space to be trimmed.
Never throws exceptions.
*/
void fz_trim_path(fz_context *ctx, fz_path *path);
MuPDF automatically calls this function when fz keep path is called for the
first time as having more than one reference to a path is considered a good
indication of it being kept around for a while.
CHAPTER 8. BUILDING BLOCKS 72
For cases where large numbers of paths are kept around for a long period of
time, for example in a fz display list (see chapter 9 Display Lists), it can be
advantageous to ‘pack’ paths to further minimise the space they use.
To pack a path, first call fz packed path size to obtain the number of bytes
required to pack a path:
/*
fz_packed_path_size: Return the number of
bytes required to pack a path.
Never throws exceptions.
*/
int fz_packed_path_size(const fz_path *path);
Then, call fz pack path with some (suitably aligned) memory of the appropri-
ate size to actually pack the path:
/*
fz_pack_path: Pack a path into the given block.
To minimise the size of paths, this function allows them to be
packed into a buffer with other information.
pack: Pointer to a block of data to pack the path into. Should
be aligned by the caller to the same alignment as required for
an fz_path pointer.
max: The number of bytes available in the block.
If max < sizeof(fz_path) then an exception will
be thrown. If max >= the value returned by
fz_packed_path_size, then this call will never
fail, except in low memory situations with large
paths.
path: The path to pack.
Paths can be ’unpacked’, ’flat’, or ’open’. Standard paths, as
created are ’unpacked’. Paths that will pack into less than max
bytes will be packed as ’flat’, unless they are too large (where
large indicates that they exceed some private implementation
defined limits, currently including having more than 256
256 coordinates or commands).
Large paths are ’open’ packed as a header into the given block,
plus pointers to other data blocks. Paths can be used
interchangably regardless of how they are packed.
Returns the number of bytes within the block used. Callers can
access the packed path data by casting the value of pack on
CHAPTER 8. BUILDING BLOCKS 73
entry to be an fz_path *.
Throws exceptions on failure to allocate, or if
max < sizeof(fz_path).
*/
int fz_pack_path(fz_context *ctx, uint8_t *pack, int max, const fz_path
*path);
After a successful call to fz pack path, the pointer to the block of memory can
be cast to an fz path * and used as normal.
All the path routines recognise packed paths and will use them interchangeably.
Packed paths may not be modified once created, however.
8.9.4 Transformation
Once a path has been constructed, a common operation is to apply a trans-
formation to it. This is equivalent to transforming every point in the existing
path. A path can be transformed using fz transform path.
/*
fz_transform_path: Transform a path by a given
matrix.
path: The path to modify (must not be a packed path).
transform: The transform to apply.
Throws exceptions if the path is packed, or on failure
to allocate.
*/
void fz_transform_path(fz_context *ctx, fz_path *path, const fz_matrix
*transform);
This counts as modifying a path of course, so ensure that you are the only
reference holder, or fz clone path it first.
8.9.5 Bounding
Sometimes it can be desirable to know the area covered by a path. The
fz bound path function enables exactly this, both for filled and stroked path.
For details of the fz stroke state structure, see subsection 8.9.6 Stroking.
/*
fz_bound_path: Return a bounding rectangle for a path.
CHAPTER 8. BUILDING BLOCKS 74
path: The path to bound.
stroke: If NULL, the bounding rectangle given is for
the filled path. If non-NULL the bounding rectangle
given is for the path stroked with the given attributes.
ctm: The matrix to apply to the path during stroking.
r: Pointer to a fz_rect which will be used to hold
the result.
*/
fz_rect *fz_bound_path(fz_context *ctx, const fz_path *path, const
fz_stroke_state *stroke, const fz_matrix *ctm, fz_rect *r);
8.9.6 Stroking
Where filling a path simply requires details of the fill to be used, stroking a
path can radically alter its appearance. The details of the stroke attributes are
passed in a fz stroke state structure.
Stroke states are created and managed with reference counting using the functi-
ons described below, but unlike other structures, the definition of the structure
itself is public. Callers are expected to alter the different fields in the struc-
ture themselves. The sole exception to this is the refs field, that should only
be altered using the usual fz keep stroke state and fz drop stroke state
mechanisms.
typedef struct fz_stroke_state_s fz_stroke_state;
typedef enum fz_linecap_e
{
FZ_LINECAP_BUTT = 0,
FZ_LINECAP_ROUND = 1,
FZ_LINECAP_SQUARE = 2,
FZ_LINECAP_TRIANGLE = 3
} fz_linecap;
typedef enum fz_linejoin_e
{
FZ_LINEJOIN_MITER = 0,
FZ_LINEJOIN_ROUND = 1,
FZ_LINEJOIN_BEVEL = 2,
FZ_LINEJOIN_MITER_XPS = 3
} fz_linejoin;
struct fz_stroke_state_s
{
int refs;
CHAPTER 8. BUILDING BLOCKS 75
fz_linecap start_cap, dash_cap, end_cap;
fz_linejoin linejoin;
float linewidth;
float miterlimit;
float dash_phase;
int dash_len;
float dash_list[32];
};
It is hoped that the meaning of the individual fields within a fz stroke state
structure are self evident to anyone working in this field. If you are unfami-
liar with any of the concepts here, see “The PDF Reference Manual” or “The
Postscript Language Reference Manual” for more details.
Most simply a reference to a stroke state structure can be obtained by calling
fz new stroke state:
/*
fz_new_stroke_state: Create a new (empty) stroke state
structure (with no dash data) and return a reference to it.
Throws exception on failure to allocate.
*/
fz_stroke_state *fz_new_stroke_state(fz_context *ctx);
For stroke states that include dash information, call:
/*
fz_new_stroke_state_with_dash_len: Create a new (empty)
stroke state structure, with room for dash data of the
given length, and return a reference to it.
len: The number of dash elements to allow room for.
Throws exception on failure to allocate.
*/
fz_stroke_state *fz_new_stroke_state_with_dash_len(fz_context *ctx, int
len);
Once obtained, references can be kept or dropped in the usual fashion:
/*
fz_keep_stroke_state: Take an additional reference to
a stroke state structure.
No modifications should be carried out on a stroke
state to which more than one reference is held, as
this can cause race conditions.
CHAPTER 8. BUILDING BLOCKS 76
Never throws exceptions.
*/
fz_stroke_state *fz_keep_stroke_state(fz_context *ctx, const
fz_stroke_state *stroke);
/*
fz_drop_stroke_state: Drop a reference to a stroke
state structure, destroying the structure if it is
the last reference.
Never throws exceptions.
*/
void fz_drop_stroke_state(fz_context *ctx, const fz_stroke_state
*stroke);
Once more than one reference is held to a stroke state, it should be considered
‘frozen’ or ‘immutable’ as other reference holders may be confused by changes to
it. Accordingly, we provide functions to ensure that we are holding a reference
to an ‘unshared’ stroke state:
/*
fz_unshare_stroke_state: Given a reference to a
(possibly) shared stroke_state structure, return
a reference to an equivalent stroke_state structure
that is guaranteed to be unshared (i.e. one that can
safely be modified).
shared: The reference to a (possibly) shared structure
to unshare. Ownership of this reference is passed in
to this function, even in the case of exceptions being
thrown.
Exceptions may be thrown in the event of failure to
allocate if required.
*/
fz_stroke_state *fz_unshare_stroke_state(fz_context *ctx,
fz_stroke_state *shared);
/*
fz_unshare_stroke_state_with_dash_len: Given a reference to a
(possibly) shared stroke_state structure, return a reference
to a stroke_state structure (with room for a given amount of
dash data) that is guaranteed to be unshared (i.e. one that
can safely be modified).
shared: The reference to a (possibly) shared structure
to unshare. Ownership of this reference is passed in
to this function, even in the case of exceptions being
thrown.
CHAPTER 8. BUILDING BLOCKS 77
Exceptions may be thrown in the event of failure to
allocate if required.
*/
fz_stroke_state *fz_unshare_stroke_state_with_dash_len(fz_context *ctx,
fz_stroke_state *shared, int len);
Finally, we have a simple function to clone a stroke state and return a new
reference to it:
/*
fz_clone_stroke_state: Create an identical stroke_state
structure and return a reference to it.
stroke: The stroke state reference to clone.
Exceptions may be thrown in the event of a failure to
allocate.
*/
fz_stroke_state *fz_clone_stroke_state(fz_context *ctx, fz_stroke_state
*stroke);
8.9.7 Walking
Given a path, it can be useful to be able to read it out again. MuPDF uses
this internally in a output devices such as the PDF or SVG devices (see sub-
section 7.5.4 PDF Output Device or subsection 7.5.6 SVG Output Device)
to convert paths to a new representation, and in the draw device (see sub-
section 7.5.2 Draw Device) for rendering.
To isolate callers from the implementation specifics of paths, MuPDF offers a
mechanism to ‘walk’ an fz path, getting a callback for each command in the
path.
typedef struct
{
/* Compulsory ones */
void (*moveto)(fz_context *ctx, void *arg, float x, float y);
void (*lineto)(fz_context *ctx, void *arg, float x, float y);
void (*curveto)(fz_context *ctx, void *arg, float x1, float y1,
float x2, float y2, float x3, float y3);
void (*closepath)(fz_context *ctx, void *arg);
/* Optional ones */
void (*quadto)(fz_context *ctx, void *arg, float x1, float y1, float
x2, float y2);
void (*curvetov)(fz_context *ctx, void *arg, float x2, float y2,
float x3, float y3);
CHAPTER 8. BUILDING BLOCKS 78
void (*curvetoy)(fz_context *ctx, void *arg, float x1, float y1,
float x3, float y3);
void (*rectto)(fz_context *ctx, void *arg, float x1, float y1, float
x2, float y2);
} fz_path_walker;
/*
fz_walk_path: Walk the segments of a path, calling the
appropriate callback function from a given set for each
segment of the path.
path: The path to walk.
walker: The set of callback functions to use. The first
4 callback pointers in the set must be non-NULL. The
subsequent ones can either be supplied, or can be left
as NULL, in which case the top 4 functions will be
called as appropriate to simulate them.
arg: An opaque argument passed in to each callback.
Exceptions will only be thrown if the underlying callback
functions throw them.
*/
void fz_walk_path(fz_context *ctx, const fz_path *path, const
fz_path_walker *walker, void *arg);
This function is called by giving a pointer to a structure containing callback
functions, one for each type of path segment type. The function will walk the
path structure and call a for each ‘segment’ of the path in turn.
Callers of this function should not rely on getting exactly the same sequence of
path segments out as was used to construct the path; the internal representation
may have been optimised to an equivalent form on construction, and this will
be reflected in the callbacks received. The path passed back will however be
entirely identical (modulo possible infinitesimal rounding issues).
For example, MuPDF is capable of spotting that a cubic or quadratic bezier
is actually a line; in such cases it may represent it as a line internally, saving
memory and processing power.
Not all path consumers can cope with the full range of segment types that
MuPDF natively supports, so some of the callback entries may be left blank
(i.e. set to NULL). Rather than calling such an entry, MuPDF will decompose
the path segment into one of the more basic types.
For example, if a path contains a quadratic segment and the quadto callback
entry is NULL, MuPDF will automatically decompose it to a bezier segment
and call the curveto entry instead.
CHAPTER 8. BUILDING BLOCKS 79
8.10 Text
8.10.1 Overview
MuPDFs central text type is an fz text structure. The exact definition of this
structure has evolved considerably in the past to accommodate the needs of dif-
ferent input formats, and it is possible this will continue in future. Accordingly
we have hidden the implementation behind an interface.
Nonetheless, it is worthwhile mentioning some of the design goals that have
influenced the development of this area of the code.
As fz text objects are the only text objects passed across the device interface,
they need to encode several layers of information. For simple rendering devi-
ces, they need to be expressive enough to allow us to exactly render the exact
specified glyphs. For text output devices, they need to be expressive enough to
allow the unicode values to be extracted.
Ideally, given any input format we would like to be able to output any output
format from it (including the same format) with no loss of data. This means
that our fz text objects need to be expressive enough to represent the super-set
of functionality of all input formats out there, even if we do not currently make
use of all the information.
Some input formats only specify glyph ids, whereas some only specify unicode
values. In order to allow us to transmute one format into another, we require
fz text objects to encapsulate both forms of data at the same time.
Some formats, that make use of glyph shaping, require us to cope with unicode
and glyph id equivalents that have no direct 1-1 correspondence.
For bidirectional text, the order in which text may be displayed on the page
may not be trivially related to the order in which it is specified in the source
file. We both need to render efficiently, and to maintain the ability to recreate
the initial logical order of the text.
Accordingly, our fz text object represents a block of text in logical order,
including font style and position, together with both unicode and glyph data
(subject to the availability of the information in the original file).
If more information is required, then details of the current implementation are
included in subsection 8.10.7 Implementation, otherwise just use it as a simple
black box.
typedef struct fz_text_s fz_text;
Text objects are reference, with the implicit understanding that once more than
one reference exists to an object, it will no longer be modified.
CHAPTER 8. BUILDING BLOCKS 80
8.10.2 Creation
Empty fz text objects can be created using the fz new text call:
/*
fz_new_text: Create a new empty fz_text object.
Throws exception on failure to allocate.
*/
fz_text *fz_new_text(fz_context *ctx);
Additional references can be taken/released in the usual manner:
/*
fz_keep_text: Add a reference to an fz_text.
text: text object to keep a reference to.
Return the same text pointer.
*/
fz_text *fz_keep_text(fz_context *ctx, const fz_text *text);
/*
fz_drop_text: Drop a reference to the object, freeing
if if is the last one.
text: Object to drop the reference to.
*/
void fz_drop_text(fz_context *ctx, const fz_text *text);
8.10.3 Population
Once created, characters can be added to the fz text object either singly:
/*
fz_show_glyph: Add a glyph/unicode value to a text object.
text: Text object to add to.
font: The font the glyph should be added in.
trm: The transform to use for the glyph.
glyph: The glyph id to add.
unicode: The unicode character for the glyph.
wmode: 1 for vertical mode, 0 for horizontal.
CHAPTER 8. BUILDING BLOCKS 81
bidi_level: The bidirectional level for this glyph.
markup_dir: The direction of the text as specified in the
markup.
language: The language in use (if known, 0 otherwise)
(e.g. FZ_LANG_zh_Hans).
Throws exception on failure to allocate.
*/
void fz_show_glyph(fz_context *ctx, fz_text *text, fz_font *font, const
fz_matrix *trm, int glyph, int unicode, int wmode, int bidi_level,
fz_bidi_direction markup_dir, fz_text_language language);
or a (unicode) string at a time:
/*
fz_show_string: Add a UTF8 string to a text object.
text: Text object to add to.
font: The font the string should be added in.
trm: The transform to use. Will be updated according
to the advance of the string on exit.
s: The utf-8 string to add.
wmode: 1 for vertical mode, 0 for horizontal.
bidi_level: The bidirectional level for this glyph.
markup_dir: The direction of the text as specified in the
markup.
language: The language in use (if known, 0 otherwise)
(e.g. FZ_LANG_zh_Hans).
Throws exception on failure to allocate.
*/
void fz_show_string(fz_context *ctx, fz_text *text, fz_font *font,
fz_matrix *trm, const char *s, int wmode, int bidi_level,
fz_bidi_direction markup_dir, fz_text_language language);
CHAPTER 8. BUILDING BLOCKS 82
8.10.4 Measurement
Once a fz text object has been created we can measure the area it will cover
on the page:
/*
fz_bound_text: Find the bounds of a given text object.
text: The text object to find the bounds of.
stroke: Pointer to the stroke attributes (for stroked
text), or NULL (for filled text).
ctm: The matrix in use.
r: pointer to storage for the bounds.
Returns a pointer to r, which is updated to contain the
bounding box for the text object.
*/
fz_rect *fz_bound_text(fz_context *ctx, const fz_text *text, const
fz_stroke_state *stroke, const fz_matrix *ctm, fz_rect *r);
8.10.5 Cloning
As stated before, fz text objects are referenced counted. Changes or manipu-
lations cannot safely be carried out on an object which might be shared with
someone else, so we provide a mechanism to clone an object. Once cloned an
object is guaranteed to be safe to modify.
/*
fz_clone_text: Clone a text object.
text: The text object to clone.
Throws an exception on allocation failure.
*/
fz_text *fz_clone_text(fz_context *ctx, const fz_text *text);
8.10.6 Language
Some formats include a declaration of which language is being used for a given
piece of text. This can be used to influence aspects of the text layout, inclu-
ding the exact choice of glyphs used in a given font. While we make relatively
CHAPTER 8. BUILDING BLOCKS 83
little use of this at present, we try to preserve the information as part of our
philosophy of not losing any information unnecessarily.
Accordingly, we use ISO 639 language specification strings, for example:
typedef enum fz_text_language_e
{
FZ_LANG_UNSET = 0,
FZ_LANG_ur = FZ_LANG_TAG2(’u’,’r’),
FZ_LANG_urd = FZ_LANG_TAG3(’u’,’r’,’d’),
FZ_LANG_ko = FZ_LANG_TAG2(’k’,’o’),
FZ_LANG_ja = FZ_LANG_TAG2(’j’,’a’),
FZ_LANG_zh = FZ_LANG_TAG2(’z’,’h’),
FZ_LANG_zh_Hans = FZ_LANG_TAG3(’z’,’h’,’s’),
FZ_LANG_zh_Hant = FZ_LANG_TAG3(’z’,’h’,’t’),
} fz_text_language;
To save space we pack these into 15 bits. Accordingly, we provide a way to
pack/unpack these to/from the more normal string representations:
/*
Convert ISO 639 (639-{1,2,3,5}) language specification
strings losslessly to a 15 bit fz_text_language code.
No validation is carried out. Obviously invalid (out
of spec) codes will be mapped to FZ_LANG_UNSET, but
well-formed (but undefined) codes will be blithely
accepted.
*/
fz_text_language fz_text_language_from_string(const char *str);
/*
Recover ISO 639 (639-{1,2,3,5}) language specification
strings losslessly from a 15 bit fz_text_language code.
No validation is carried out. See note above.
*/
char *fz_string_from_text_language(char str[8], fz_text_language lang);
8.10.7 Implementation
A fz text structure represents a block of text. At the lowest level the consti-
tuents of a block are fz text items.
typedef struct fz_text_item_s fz_text_item;
struct fz_text_item_s
CHAPTER 8. BUILDING BLOCKS 84
{
float x, y;
int gid; /* -1 for one gid to many ucs mappings */
int ucs; /* -1 for one ucs to many gid mappings */
};
The items can be thought of as the individual ‘characters’ that make up the
display, together with their position. Where possible, we attempt to give both
the glyph id (gid) and the unicode value (ucs) for the character, but there are
various cases where a 1-1 mapping is not possible.
Some unicode characters can result in a string of glyphs. The glyph ids will be
sent in a series of fz text items, in which the first ucs value will be the source
unicode character, and subsequent ones will be -1.
Some sequences of unicode characters can result in a single glyph. Again, a
sequence of fz text items will be sent listing the unicode values, but all but
the first item will have the gid value set to -1.
In more complex cases, sequences of unicode characters can be transformed into
a sequence of glyphs, with no direct correspondence between the source text
and the output characters. In this case as many fz text items as are required
are used, with either the gid or ucs values padded out by -1s as necessary.
Different input formats offer the text in different forms. With PDF, the data
within the file is (typically) in the form of glyph ids, and mechanisms are optio-
nally provided to infer unicode values from them. Glyphs are sent in any order,
and absolutely positioned on the page.
With XPS the input can be either in the form of unicode or glyph ids, and
directionality information is encoded in the file. This means that the logical
ordering of the glyphs is well defined.
Some formats, such as EPub and HTML, send unicode text with even less
positioning information, and rely on the interpreter to perform layout. Part
of this process involves inferring directional information from the source text,
and then using shaping mechanisms embedded within the font to do complex
conversions to give the final positioned glyph sequences.
In all such cases MuPDF will preserve the logical ordering of the unicode entries,
at the cost of drawing glyphs non-monotonically onto the page.
Sequences of fz text items that share the same characteristics are gathered
together into fz text spans:
struct fz_text_span_s
{
fz_font *font;
fz_matrix trm;
unsigned wmode : 1; /* 0 horizontal, 1 vertical */
CHAPTER 8. BUILDING BLOCKS 85
unsigned bidi_level : 7; /* The bidirectional level of text */
unsigned markup_dir : 2; /* The direction of text as marked in the
original document */
unsigned language : 15; /* The language as marked in the original
document */
int len, cap;
fz_text_item *items;
fz_text_span *next;
};
Sequences of these spans are then gathered up into a linked list rooted in a
fz text.
struct fz_text_s
{
int refs;
fz_text_span *head, *tail;
};
8.11 Shadings
8.11.1 Overview
One of the most powerful graphical effects within PDF and other input formats
is that of Shadings. Our central type representing shadings, fz shade is all that
we have to pass details of shadings across the fz device interface.
Consequently, we need fz shade to be expressive enough to cope with shadings
from all possible sources, and yet we would like to avoid having to reproduce
the shade handling code in all devices.
Accordingly, fz shade is defined to be expressive enough to encapsulate all
the different shading representations found in PDF with the data essentially
unchanged. PDF is currently the super-set of shadings found in other formats.
If this changes, fz shade will be extended as required.
typedef struct fz_shade_s
{
fz_storable storable;
fz_rect bbox; /* can be fz_infinite_rect */
fz_colorspace *colorspace;
fz_matrix matrix; /* matrix from pattern dict */
int use_background; /* background color for fills but not ’sh’ */
float background[FZ_MAX_COLORS];
CHAPTER 8. BUILDING BLOCKS 86
int use_function;
float function[256][FZ_MAX_COLORS + 1];
int type; /* function, linear, radial, mesh */
union
{
struct
{
int extend[2];
float coords[2][3]; /* (x,y,r) twice */
} l_or_r;
struct
{
int vprow;
int bpflag;
int bpcoord;
int bpcomp;
float x0, x1;
float y0, y1;
float c0[FZ_MAX_COLORS];
float c1[FZ_MAX_COLORS];
} m;
struct[]
{
fz_matrix matrix;
int xdivs;
int ydivs;
float domain[2][2];
float *fn_vals;
} f;
} u;
fz_compressed_buffer *buffer;
} fz_shade;
8.11.2 Creation
Currently, there is no defined API for creating a shading due to the public nature
of the structure. Just call fz malloc struct(ctx, fz shade) and initialise the
fields accordingly.
We may look to add convenience functions in the future, as this is likely to be
desirable for the JNI (and other) bindings.
Shading objects are reference counted, with the implicit understanding that once
more than one reference exists to a fz shade, it will no longer be modified.
CHAPTER 8. BUILDING BLOCKS 87
Additional references can be taken and dropped as usual:
/*
fz_keep_shade: Add a reference to an fz_shade.
shade: The reference to keep.
Returns shade.
*/
fz_shade *fz_keep_shade(fz_context *ctx, fz_shade *shade);
/*
fz_drop_shade: Drop a reference to an fz_shade.
shade: The reference to drop. If this is the last
reference, shade will be destroyed.
*/
void fz_drop_shade(fz_context *ctx, fz_shade *shade);
We also provide a function to process a given shading, by calling
8.11.3 Bounding
Once created, we can ask for the bounds of a given shade under a given trans-
formation. This can sometimes be infinite.
/*
fz_bound_shade: Bound a given shading.
shade: The shade to bound.
ctm: The transform to apply to the shade before bounding.
r: Pointer to storage to put the bounds in.
Returns r, updated to contain the bounds for the shading.
*/
fz_rect *fz_bound_shade(fz_context *ctx, fz_shade *shade, const
fz_matrix *ctm, fz_rect *r);
8.11.4 Painting
For devices that require shadings as rasterised objects, we provide a function to
paint a shading to an fz pixmap:
/*
CHAPTER 8. BUILDING BLOCKS 88
fz_paint_shade: Render a shade to a given pixmap.
shade: The shade to paint.
ctm: The transform to apply.
dest: The pixmap to render into.
bbox: Pointer to a bounding box to limit the rendering
of the shade.
*/
void fz_paint_shade(fz_context *ctx, fz_shade *shade, const fz_matrix
*ctm, fz_pixmap *dest, const fz_irect *bbox);
This is currently used by the draw and SVG devices.
8.11.5 Decomposition
For devices that wish to get access to a higher level representation of a shading,
but do not wish to access the internals of a shading directly, we provide a
function to decompose a shading to a mesh.
This is called with functions to ‘prepare’ and ‘fill’ vertices respectively. The
mesh is decomposed to triangles internally, each vertex is ‘prepared’ and each
triangle ‘filled’ in turn.
The ordering of these calls is not guaranteed, other than the fact that a vertex
will always be prepared before it is used as part of a triangle to be filled.
typedef struct fz_vertex_s fz_vertex;
struct fz_vertex_s
{
fz_point p;
float c[FZ_MAX_COLORS];
};
/*
fz_shade_prepare_fn: Callback function type for use with
fz_process_shade.
arg: Opaque pointer from fz_process_shade caller.
v: Pointer to a fz_vertex structure to populate.
c: Pointer to an array of floats to use to populate v.
*/
CHAPTER 8. BUILDING BLOCKS 89
typedef void (fz_shade_prepare_fn)(fz_context *ctx, void *arg, fz_vertex
*v, const float *c);
/*
fz_shade_process_fn: Callback function type for use with
fz_process_shade.
arg: Opaque pointer from fz_process_shade caller.
av, bv, cv: Pointers to a fz_vertex structure describing
the corner locations and colors of a triangle to be
filled.
*/
typedef void (fz_shade_process_fn)(fz_context *ctx, void *arg, fz_vertex
*av, fz_vertex *bv, fz_vertex *cv);
/*
fz_process_shade: Process a shade, using supplied callback
functions. This decomposes the shading to a mesh (even ones
that are not natively meshes, such as linear or radial
shadings), and processes triangles from those meshes.
shade: The shade to process.
ctm: The transform to use
prepare: Callback function to ’prepare’ each vertex.
This function is passed an array of floats, and populates
an fz_vertex structure.
process: This function is passed 3 pointers to vertex
structures, and actually performs the processing (typically
filling the area between the vertexes).
process_arg: An opaque argument passed through from caller
to callback functions.
*/
void fz_process_shade(fz_context *ctx, fz_shade *shade, const fz_matrix
*ctm,
fz_shade_prepare_fn *prepare, fz_shade_process_fn *process,
void *process_arg);
This function is used internally as part of fz paint shade, but is intended to
also allow extraction of arbitrary shading data.
Chapter 9
Display Lists
9.0.1 Overview
While MuPDF is engineered to be as fast as possible at interpreting page con-
tents, there is inevitably some overhead in converting from the documents native
format to the stream of graphical operations (calls over the fz device interface).
If you are planning to redraw the same page several times (perhaps because you
are panning and zooming around a page in a viewer), then it can be advanta-
geous to use a display List.
A display list is simply a way of packaging up a stream of graphical operations
so that they can be efficiently played back, possibly with different transforms
or clip rectangles.
Display lists are optimised to use as little memory as possible, but clearly are
(typically) a greater user of memory than just reinterpreting the file. The big
advantage of display lists, other than their speed, is that they can safely be
played back without touching the underlying file. This means they can be used
in other threads without having to worry about contention.
Display lists are implemented within using MuPDF using the fz display list
type.
9.0.2 Creation
An empty display list can be created by the fz new display list call.
/*
fz_new_display_list: Create an empty display list.
A display list contains drawing commands (text, images, etc.).
90
CHAPTER 9. DISPLAY LISTS 91
Use fz_new_list_device for populating the list.
mediabox: Bounds of the page (in points) represented by the display
list.
*/
fz_display_list *fz_new_display_list(fz_context *ctx, const fz_rect
*mediabox);
Once created it can be populated by creating a display list device instance that
writes to it.
/*
fz_new_list_device: Create a rendering device for a display list.
When the device is rendering a page it will populate the
display list with drawing commands (text, images, etc.). The
display list can later be reused to render a page many times
without having to re-interpret the page from the document file
for each rendering. Once the device is no longer needed, free
it with fz_drop_device.
list: A display list that the list device takes ownership of.
*/
fz_device *fz_new_list_device(fz_context *ctx, fz_display_list *list);
Once you have created such a display list device, any calls made to that device
(such as by calling fz run page or similar) will be recorded into the display list.
When you have finished writing to the display list (remembering to
call fz close device), you dispose of the device as normal (by calling
fz drop device). This leaves you holding the sole reference to the display
list itself.
Writing to a display list is not thread safe. That is to say, do not attempt to
write to a display list from more than one thread at a time. Similarly, do not
attempt to read from display lists while write operations are ongoing.
9.0.3 Playback
To playback from a list, just call fz run display list.
/*
fz_run_display_list: (Re)-run a display list through a device.
list: A display list, created by fz_new_display_list and
populated with objects from a page by running fz_run_page on a
device obtained from fz_new_list_device.
CHAPTER 9. DISPLAY LISTS 92
dev: Device obtained from fz_new_*_device.
ctm: Transform to apply to display list contents. May include
for example scaling and rotation, see fz_scale, fz_rotate and
fz_concat. Set to fz_identity if no transformation is desired.
area: Only the part of the contents of the display list
visible within this area will be considered when the list is
run through the device. This does not imply for tile objects
contained in the display list.
cookie: Communication mechanism between caller and library
running the page. Intended for multi-threaded applications,
while single-threaded applications set cookie to NULL. The
caller may abort an ongoing page run. Cookie also communicates
progress information back to the caller. The fields inside
cookie are continually updated while the page is being run.
*/
void fz_run_display_list(fz_context *ctx, fz_display_list *list,
fz_device *dev, const fz_matrix *ctm, const fz_rect *area,
fz_cookie *cookie);
9.0.4 Reference counting
In common with most other objects in MuPDF, fz display lists are reference
counted. This means that once you have finished with a reference to a display
list, it can safely be disposed of by calling fz drop display list.
/*
fz_drop_display_list: Drop a reference to a display list, freeing it
if the reference count reaches zero.
Does not throw exceptions.
*/
void fz_drop_display_list(fz_context *ctx, fz_display_list *list);
Should you wish to keep a new reference to a display list, you can generate one
using fz keep display list.
/*
fz_keep_display_list: Keep a reference to a display list.
Does not throw exceptions.
*/
fz_display_list *fz_keep_display_list(fz_context *ctx, fz_display_list
*list);
CHAPTER 9. DISPLAY LISTS 93
In general, it is rare for you to want to make a new reference to a display list
until write operations on one have finished. It is good form to avoid this.
9.0.5 Miscellaneous operations
There are a few other operations that can be performed efficiently on a display
list. Firstly, one can request the bounds of a list.
/*
fz_bound_display_list: Return the bounding box of the page recorded
in a display list.
*/
fz_rect *fz_bound_display_list(fz_context *ctx, fz_display_list *list,
fz_rect *bounds);
Secondly, one can create a new fz image from a display list. This is useful
for creating scalable content to embed in other document types; for instance
MuPDF makes use of this to turn SVG files embedded within epub files (for
illustrations and cover pages etc) into convenient objects for adding into the
flow of text.
/*
Create a new image from a display list.
w, h: The conceptual width/height of the image.
transform: The matrix that needs to be applied to the given
list to make it render to the unit square.
list: The display list.
*/
fz_image *fz_new_image_from_display_list(fz_context *ctx, float w, float
h, fz_display_list *list);
Finally, it is possible to very quickly check if a given display list is empty or not.
/*
Check for a display list being empty
list: The list to check.
Returns true if empty, false otherwise.
*/
int fz_display_list_is_empty(fz_context *ctx, const fz_display_list
*list);
Chapter 10
The Stream interface
10.1 Overview
MuPDF is designed to run in a variety of different environments. As such,
this means input can come from many different sources. On desktop computers
input may come as files on backing store. For web served files, input may be
streamed over a network. For systems with DRM embedded, the data may need
to be decoded on the fly.
Similarly, data can be encapsulated within different formats in different ways,
with multiple layers of encoding.
Accordingly, MuPDF abstracts the idea of an ‘input stream’ to a reusable class,
fz stream. Many implementations of fz streams are given by default in the
core library, but the abstract nature of this class allows callers to provide im-
plementations of their own to seamlessly extend the systems capabilities as
required.
10.2 Creation
The exact mechanism for creating a stream depends upon the source for that
particular stream, but typically it will involve a call to a creation function, such
as fz
open file.
/*
fz_open_file: Open the named file and wrap it in a stream.
filename: Path to a file. On non-Windows machines the filename should
be exactly as it would be passed to fopen(2). On Windows machines,
the path should be UTF-8 encoded so that non-ASCII characters can be
94
CHAPTER 10. THE STREAM INTERFACE 95
represented. Other platforms do the encoding as standard anyway (and
in most cases, particularly for MacOS and Linux, the encoding they
use is UTF-8 anyway).
*/
fz_stream *fz_open_file(fz_context *ctx, const char *filename);
Alternative functions exist to allow creating streams from C level FILE pointers:
/*
fz_open_file: Wrap an open file descriptor in a stream.
file: An open file descriptor supporting bidirectional
seeking. The stream will take ownership of the file
descriptor, so it may not be modified or closed after the call
to fz_open_file_ptr. When the stream is closed it will also close
the file descriptor.
*/
fz_stream *fz_open_file_ptr(fz_context *ctx, FILE *file);
from direct memory blocks:
/*
fz_open_memory: Open a block of memory as a stream.
data: Pointer to start of data block. Ownership of the data block is
NOT passed in.
len: Number of bytes in data block.
Returns pointer to newly created stream. May throw exceptions on
failure to allocate.
*/
fz_stream *fz_open_memory(fz_context *ctx, unsigned char *data, size_t
len);
and from fz buffers:
/*
fz_open_buffer: Open a buffer as a stream.
buf: The buffer to open. Ownership of the buffer is NOT passed in
(this function takes its own reference).
Returns pointer to newly created stream. May throw exceptions on
failure to allocate.
*/
fz_stream *fz_open_buffer(fz_context *ctx, fz_buffer *buf);
There are too many other options for creating streams to list them all here, but
CHAPTER 10. THE STREAM INTERFACE 96
their use should be self evident from the header file definitions. Once created,
all streams can be used in the same ways.
10.3 Usage
10.3.1 Reading bytes
The simplest way to read bytes from a stream is to call fz read byte to read
the next byte from a file. Akin to the standard fgetc, this returns -1 for end
of data, or the next byte available.
/*
fz_read_byte: Read the next byte from a stream.
stm: The stream t read from.
Returns -1 for end of stream, or the next byte. May
throw exceptions.
*/
int fz_read_byte(fz_context *ctx, fz_stream *stm);
To read more than 1 byte at a time, there are two different options.
Firstly, and most efficiently, bytes can be read directly from the streams under-
lying buffer. For a given fz stream *stm, the current position in the stream is
pointed to by stm->rp. Bytes can simply be read out, and the pointer incre-
mented by the number read.
To do this, you must first know how many bytes there are available to be read
out. This is achieved by calling fz available. If there are no bytes already
decoded and awaiting reading, this call will trigger a refill of the underlying
buffer, which may take noticeable time.
/*
fz_available: Ask how many bytes are available immediately from
a given stream.
stm: The stream to read from.
max: A hint for the underlying stream; the maximum number of
bytes that we are sure we will want to read. If you do not know
this number, give 1.
Returns the number of bytes immediately available between the
read and write pointers. This number is guaranteed only to be 0
if we have hit EOF. The number of bytes returned here need have
no relation to max (could be larger, could be smaller).
CHAPTER 10. THE STREAM INTERFACE 97
*/
size_t fz_available(fz_context *ctx, fz_stream *stm, size_t max);
To avoid needless work, a ‘max’ value can be supplied as a hint, telling any
buffer refill operation that is triggered how many bytes are actually required.
Specifying a max value does not guarantee you anything about the number of
bytes actually made available.
Some callers may find this awkward - the need to potentially repeatedly call
until you get enough bytes to fill a buffer of the required length may be tedious.
Therefore as an alternative, we provide a simpler call, fz read.
Designed to be similar to the standard fread call, this attempts to read as
many bytes as possible into a supplied data block, returning the actual number
of bytes successfully read.
/*
fz_read: Read from a stream into a given data block.
stm: The stream to read from.
data: The data block to read into.
len: The length of the data block (in bytes).
Returns the number of bytes read. May throw exceptions.
*/
size_t fz_read(fz_context *ctx, fz_stream *stm, unsigned char *data,
size_t len);
Typically the only reason that fz read will not return the requested number of
bytes is if we hit the end of the stream. This implies that calls to fz read will
block until such data is ready. For streams based on ‘fast’ sources like files or
memory, this is an unimportant distinction.
For streams based on (say) an http download, this might result in significant
delays, and an unacceptable user experience. To alleviate this problem we have
a mechanism whereby such streams can signal a temporary end of data by
throwing the FZ ERROR TRYLATER error. See chapter 16 Progressive Mode for
more details.
To facilitate reading without blocking (or using buffers larger than required),
fz available can be called to find out the number of bytes that can safely be
requested.
If data within a stream is not required, it can be skipped over using fz skip:
/*
fz_skip: Read from a stream discarding data.
CHAPTER 10. THE STREAM INTERFACE 98
stm: The stream to read from.
len: The number of bytes to read.
Returns the number of bytes read. May throw exceptions.
*/
size_t fz_skip(fz_context *ctx, fz_stream *stm, size_t len);
As a special case, after a single byte is read, it can be pushed back into the
stream, using fz unread byte:
/*
fz_unread_byte: Unread the single last byte successfully
read from a stream. Do not call this without having
successfully read a byte.
*/
void fz_unread_byte(fz_context *ctx FZ_UNUSED, fz_stream *stm);
The act of reading a byte, and then, if successful pushing it back again is
encapsulated in a convenience function, fz peek byte:
/*
fz_peek_byte: Peek at the next byte in a stream.
stm: The stream to peek at.
Returns -1 for EOF, or the next byte that will be read.
*/
int fz_peek_byte(fz_context *ctx, fz_stream *stm);
10.3.2 Reading objects
Often, when parsing different document formats, it can be useful to read specific
objects from streams, so convenience functions exist for this too. Firstly, integers
of different size and endianness are catered for:
/*
fz_read_[u]int(16|24|32|64)(_le)?
Read a 16/32/64 bit signed/unsigned integer from stream,
in big or little-endian byte orders.
Throws an exception if EOF is encountered.
*/
uint16_t fz_read_uint16(fz_context *ctx, fz_stream *stm);
uint32_t fz_read_uint24(fz_context *ctx, fz_stream *stm);
uint32_t fz_read_uint32(fz_context *ctx, fz_stream *stm);
CHAPTER 10. THE STREAM INTERFACE 99
uint64_t fz_read_uint64(fz_context *ctx, fz_stream *stm);
uint16_t fz_read_uint16_le(fz_context *ctx, fz_stream *stm);
uint32_t fz_read_uint24_le(fz_context *ctx, fz_stream *stm);
uint32_t fz_read_uint32_le(fz_context *ctx, fz_stream *stm);
uint64_t fz_read_uint64_le(fz_context *ctx, fz_stream *stm);
int16_t fz_read_int16(fz_context *ctx, fz_stream *stm);
int32_t fz_read_int32(fz_context *ctx, fz_stream *stm);
int64_t fz_read_int64(fz_context *ctx, fz_stream *stm);
int16_t fz_read_int16_le(fz_context *ctx, fz_stream *stm);
int32_t fz_read_int32_le(fz_context *ctx, fz_stream *stm);
int64_t fz_read_int64_le(fz_context *ctx, fz_stream *stm);
We have functions to read both C style strings, and newline/return terminated
lines:
/*
fz_read_string: Read a null terminated string from the stream into
a buffer of a given length. The buffer will be null terminated.
Throws on failure (including the failure to fit the entire string
including the terminator into the buffer).
*/
void fz_read_string(fz_context *ctx, fz_stream *stm, char *buffer, int
len);
/*
fz_read_line: Read a line from stream into the buffer until either a
terminating newline or EOF, which it replaces with a null byte
(’\0’).
Returns buf on success, and NULL when end of file occurs while no
characters
have been read.
*/
char *fz_read_line(fz_context *ctx, fz_stream *stm, char *buf, size_t
max);
10.3.3 Reading bits
Streams (or sections of streams) can be treated as a string of bits, packed either
most significant or least significant bits first.
To read from an msb packed stream, use fz read bits:
/*
fz_read_bits: Read the next n bits from a stream (assumed to
CHAPTER 10. THE STREAM INTERFACE 100
be packed most significant bit first).
stm: The stream to read from.
n: The number of bits to read, between 1 and 8*sizeof(int)
inclusive.
Returns (unsigned int)-1 for EOF, or the required number of bits.
*/
unsigned int fz_read_bits(fz_context *ctx, fz_stream *stm, int n);
Conversely, to read from a lsb packed stream, use fz read rbits:
/*
fz_read_rbits: Read the next n bits from a stream (assumed to
be packed least significant bit first).
stm: The stream to read from.
n: The number of bits to read, between 1 and 8*sizeof(int)
inclusive.
Returns (unsigned int)-1 for EOF, or the required number of bits.
*/
unsigned int fz_read_rbits(fz_context *ctx, fz_stream *stm, int n);
;
Whichever of these is used, reading n bits will return the results in the lowest
n bits of the returned value.
After reading bits using these functions, if a return to reading bytewise (or
objectwise) is required, then fz sync bits must be called.
/*
fz_sync_bits: Called after reading bits to tell the stream
that we are about to return to reading bytewise. Resyncs
the stream to whole byte boundaries.
*/
void fz_sync_bits(fz_context *ctx FZ_UNUSED, fz_stream *stm);
10.3.4 Reading whole streams
As a convenience function, MuPDF provides a mechanism for reading the entire
contents of a stream into an fz buffer.
/*
fz_read_all: Read all of a stream into a buffer.
CHAPTER 10. THE STREAM INTERFACE 101
stm: The stream to read from
initial: Suggested initial size for the buffer.
Returns a buffer created from reading from the stream. May throw
exceptions on failure to allocate.
*/
fz_buffer *fz_read_all(fz_context *ctx, fz_stream *stm, size_t initial);
This will throw an error (and hence not return any data) if an error is encoun-
tered during the decode of the stream. Sometimes it can be preferable to ‘do
the best we can’ and tolerate problematic data. For such cases, we provide
fz read best:
/*
fz_read_best: Attempt to read a stream into a buffer. If truncated
is NULL behaves as fz_read_all, otherwise does not throw exceptions
in the case of failure, but instead sets a truncated flag.
stm: The stream to read from.
initial: Suggested initial size for the buffer.
truncated: Flag to store success/failure indication in.
Returns a buffer created from reading from the stream.
*/
fz_buffer *fz_read_best(fz_context *ctx, fz_stream *stm, size_t initial,
int *truncated);
10.3.5 Seeking
Most stream operations simply advance the stream pointer as the stream is read.
The current stream position can always be obtained using fz tell (deliberately
similar to the standard ftell call):
/*
fz_tell: return the current reading position within a stream
*/
fz_off_t fz_tell(fz_context *ctx, fz_stream *stm);
Some streams allow you to seek within them, that is, to change the current
stream pointer to a given offset. To do this, use fz seek (deliberately similar
to fseek):
/*
CHAPTER 10. THE STREAM INTERFACE 102
fz_seek: Seek within a stream.
stm: The stream to seek within.
offset: The offset to seek to.
whence: From where the offset is measured (see fseek).
*/
void fz_seek(fz_context *ctx, fz_stream *stm, fz_off_t offset, int
whence);
In the event that a stream does not support seeking, an error will be thrown.
10.3.6 Meta data
Occasionally, it can be useful to interrogate the properties of a stream, for
example the length of the stream, or whether it is coming from a progressive
source (see chapter 16 Progressive Mode).
While not implemented currently, perhaps in future a particular stream user
might want to interrogate information about the Mimetype of the stream, or its
compression ratios.
To allow this, we have an extensible system to request Meta operations on a
stream. The fz stream meta function allows such calls to be made, with a
reason code to identify the required operation, and pointer and size parameters
to identify data to be passed:
/*
fz_stream_meta: Perform a meta call on a stream (typically to
request meta information about a stream).
stm: The stream to query.
key: The meta request identifier.
size: Meta request specific parameter - typically the size of
the data block pointed to by ptr.
ptr: Meta request specific parameter - typically a pointer to
a block of data to be filled in.
Returns -1 if this stream does not support this meta operation,
or a meta operation specific return value.
*/
int fz_stream_meta(fz_context *ctx, fz_stream *stm, int key, int size,
void *ptr);
CHAPTER 10. THE STREAM INTERFACE 103
10.3.7 Destruction
In common with most other MuPDF objects, fz streams are reference counted.
As such additional references can be taken using fz keep stream and they can
be destroyed using fz drop stream.
Note that care must be taken not to use fz stream objects simultaneously in
more than one thread. Not only does the act of reading in one thread upset
the point at which the next read will happen in another thread, no protection
is provided to make operations atomic - thus the internal data can become
corrupted and cause crashes.
10.4 Implementing an fz stream
The above, relatively rich, set of functions are implemented on a fairly simple
basic structure.
To implement your own fz stream, simply define a creation function, of the
form:
fz_stream *fz_new_stream_foo(fz_context *ctx, <more parameters here>)
{
fz_stream *stm;
foo_state *state;
state = <create structure to hold foo specific stream state>
stm = fz_new_stream(ctx, state, foo_next, foo_close);
<set stm->seek if required>
<set stm->meta if required>
return stm;
}
Note that some fz try/fz catch-ery may be required as part of the setup for
state.
The hard work for this function is done using fz new stream, and two ‘foo’
specific functions, foo next and foo close. First let’s look at fz new stream:
/*
fz_new_stream: Create a new stream object with the given
internal state and function pointers.
state: Internal state (opaque to everything but implementation).
next: Should provide the next set of bytes (up to max) of stream
data. Return the number of bytes read, or EOF when there is no
more data.
CHAPTER 10. THE STREAM INTERFACE 104
close: Should clean up and free the internal state. May not
throw exceptions.
*/
fz_stream *fz_new_stream(fz_context *ctx, void *state, fz_stream_next_fn
*next, fz_stream_close_fn *close);
This creates the main fz stream structure, populates it with the given pointers
(state, foo next and foo close) and sets the internal buffer pointers up to
indicate an empty buffer.
As soon as anyone tries to read from the buffer (or to find out how many bytes
are available), the MuPDF stream functions will cause foo next to be called.
This is a function of the following type:
/*
fz_stream_next_fn: A function type for use when implementing
fz_streams. The supplied function of this type is called
whenever data is required, and the current buffer is empty.
stm: The stream to operate on.
max: a hint as to the maximum number of bytes that the caller
needs to be ready immediately. Can safely be ignored.
Returns -1 if there is no more data in the stream. Otherwise,
the function should find its internal state using stm->state,
refill its buffer, update stm->rp and stm->wp to point to the
start and end of the new data respectively, and then
"return *stm->rp++".
*/
typedef int (fz_stream_next_fn)(fz_context *ctx, fz_stream *stm, size_t
max);
When the stream is closed, the foo close function will be called. This should
be a function of type fz stream close fn:
/*
fz_stream_close_fn: A function type for use when implementing
fz_streams. The supplied function of this type is called
when the stream is closed, to release the stream specific
state information.
state: The stream state to release.
*/
In our example, if the state was created by a simple fz malloc struct(ctx,
foo state) then foo close might be as simple as an fz free(ctx, state).
If the internal state of the stream is more complex then the destructor will be
CHAPTER 10. THE STREAM INTERFACE 105
similarly more complex.
These three functions (creation, next and close) are all that is required to define
a stream.
Optionally, you can also define a seek and/or a meta function, using functions
of the following types:
/*
fz_stream_seek_fn: A function type for use when implementing
fz_streams. The supplied function of this type is called when
fz_seek is requested, and the arguments are as defined for
fz_seek.
The stream can find its private state in stm->state.
*/
typedef void (fz_stream_seek_fn)(fz_context *ctx, fz_stream *stm,
fz_off_t offset, int whence);
/*
fz_stream_meta_fn: A function type for use when implementing
fz_streams. The supplied function of this type is called when
fz_meta is requested, and the arguments are as defined for
fz_meta.
The stream can find its private state in stm->state.
*/
typedef int (fz_stream_meta_fn)(fz_context *ctx, fz_stream *stm, int
key, int size, void *ptr);
Chapter 11
The Output interface
11.1 Overview
In the same way as fz streams abstracts input streams, MuPDF uses a reusable
class, fz output, to abstract output streams.
11.2 Creation
The exact function to call to create an output stream depends on the specific
stream required, but they generally follow a similar format. Some common
examples are:
/*
fz_new_output_with_file: Open an output stream that writes to a
FILE *.
file: The file to write to.
close: non-zero if we should close the file when the fz_output
is closed.
*/
fz_output *fz_new_output_with_file_ptr(fz_context *ctx, FILE *file, int
close);
/*
fz_new_output_with_path: Open an output stream that writes to a
given path.
filename: The filename to write to (specified in UTF-8).
106
CHAPTER 11. THE OUTPUT INTERFACE 107
append: non-zero if we should append to the file, rather than
overwriting it.
*/
fz_output *fz_new_output_with_path(fz_context *, const char *filename,
int append);
/*
fz_new_output_with_buffer: Open an output stream that appends
to a buffer.
buf: The buffer to append to.
*/
fz_output *fz_new_output_with_buffer(fz_context *ctx, fz_buffer *buf);
One of the most common use cases is to get an output stream that goes to stdout
or stderr, and we provide convenience functions for exactly this. In addition we
allow the streams for stdout and stderr to be replaced by other fz outputs,
thus allowing redirection to be changed simply for any of our existing tools:
/*
fz_stdout: The standard out output stream. By default
this stream writes to stdout. This may be overridden
using fz_set_stdout.
*/
fz_output *fz_stdout(fz_context *ctx);
/*
fz_stderr: The standard error output stream. By default
this stream writes to stderr. This may be overridden
using fz_set_stderr.
*/
fz_output *fz_stderr(fz_context *ctx);
/*
fz_set_stdout: Replace default standard output stream
with a given stream.
out: The new stream to use.
*/
void fz_set_stdout(fz_context *ctx, fz_output *out);
/*
fz_set_stderr: Replace default standard error stream
with a given stream.
err: The new stream to use.
*/
void fz_set_stderr(fz_context *ctx, fz_output *err);
CHAPTER 11. THE OUTPUT INTERFACE 108
11.3 Usage
11.3.1 Writing bytes
Single bytes can be written to fz output streams using fz write byte:
/*
fz_write_byte: Write a single byte.
out: stream to write to.
x: value to write
*/
void fz_write_byte(fz_context *ctx, fz_output *out, unsigned char x);
Blocks of bytes can be written to fz output streams using fz write:
/*
fz_write: Write data to output. Designed to parallel
fwrite.
out: Output stream to write to.
data: Pointer to data to write.
size: Length of data to write.
*/
void fz_write(fz_context *ctx, fz_output *out, const void *data, size_t
size);
11.3.2 Writing objects
We have convenience functions for outputting 16 and 32bit integers in both big
and little endian forms:
/*
fz_write_int32_be: Write a big-endian 32-bit binary integer.
*/
void fz_write_int32_be(fz_context *ctx, fz_output *out, int x);
/*
fz_write_int32_le: Write a little-endian 32-bit binary integer.
*/
void fz_write_int32_le(fz_context *ctx, fz_output *out, int x);
/*
fz_write_int16_be: Write a big-endian 16-bit binary integer.
CHAPTER 11. THE OUTPUT INTERFACE 109
*/
void fz_write_int16_be(fz_context *ctx, fz_output *out, int x);
/*
fz_write_int16_le: Write a little-endian 16-bit binary integer.
*/
void fz_write_int16_le(fz_context *ctx, fz_output *out, int x);
And a function for outputting utf-8 encoded unicode characters:
/*
fz_write_rune: Write a UTF-8 encoded unicode character.
*/
void fz_write_rune(fz_context *ctx, fz_output *out, int rune);
11.3.3 Writing strings
To output printable strings, we have the simple fputc, fputs and fputrune
equivalents:
/*
fz_putc: fputc equivalent for output streams.
*/
#define fz_putc(C,O,B) fz_write_byte(C, O, B)
/*
fz_puts: fputs equivalent for output streams.
*/
#define fz_puts(C,O,S) fz_write(C, O, (S), strlen(S))
/*
fz_putrune: fputrune equivalent for output streams.
*/
#define fz_putrune(C,O,R) fz_write_rune(C, O, R)
We also provide a family of enhanced output functions, patterned after fprintf:
/*
fz_vsnprintf: Our customised vsnprintf routine.
Takes %c, %d, %o, %s, %u, %x, as usual.
Modifiers are not supported except for zero-padding
ints (e.g. %02d, %03o, %04x, etc).
%f and %g both output in "as short as possible hopefully lossless
non-exponent" form, see fz_ftoa for specifics.
%C outputs a utf8 encoded int.
%M outputs a fz_matrix*.
%R outputs a fz_rect*.
CHAPTER 11. THE OUTPUT INTERFACE 110
%P outputs a fz_point*.
%q and %( output escaped strings in C/PDF syntax.
%ll{d,u,x} indicates that the values are 64bit.
%z{d,u,x} indicates that the value is a size_t.
%Z{d,u,x} indicates that the value is a fz_off_t.
*/
size_t fz_vsnprintf(char *buffer, size_t space, const char *fmt, va_list
args);
/*
fz_snprintf: The non va_list equivalent of fz_vsnprintf.
*/
size_t fz_snprintf(char *buffer, size_t space, const char *fmt, ...);
/*
fz_printf: fprintf equivalent for output streams. See fz_snprintf.
*/
void fz_printf(fz_context *ctx, fz_output *out, const char *fmt, ...);
/*
fz_vprintf: vfprintf equivalent for output streams. See fz_vsnprintf.
*/
void fz_vprintf(fz_context *ctx, fz_output *out, const char *fmt,
va_list ap);
11.3.4 Seeking
As with fz streams, fz outputs normally move linearly, but in special cases,
can be seekable.
/*
fz_seek_output: Seek to the specified file position. See fseek
for arguments.
Throw an error on unseekable outputs.
*/
void fz_seek_output(fz_context *ctx, fz_output *out, fz_off_t off, int
whence);
Unlike fz streams, which support fz tell in all cases, fz outputs can only
fz tell output if they are seekable:
/*
fz_tell_output: Return the current file position. Throw an error
on unseekable outputs.
*/
fz_off_t fz_tell_output(fz_context *ctx, fz_output *out);
CHAPTER 11. THE OUTPUT INTERFACE 111
11.4 Implementing a fz output
The above, relatively rich, set of functions are implemented on a fairly simple
basic structure.
To implement your own fz output, simply define a creation function of the
form:
fz_output *fz_new_output_foo(fz_context *ctx, <more parameters here>)
{
fz_output *out = fz_new_output(ctx, <state>, foo_write, foo_close);
<optionally set out->seek = foo_seek>
<optionally set out->tell = foo_tell>
return out;
}
This has parallels with the implementation of fz streams, but is not quite
identical.
If ¡state¿ needs no destruction, then we can use NULL in place of foo close.
Otherwise foo close should be a function of type:
/*
fz_output_close_fn: A function type for use when implementing
fz_outputs. The supplied function of this type is called
when the output stream is closed, to release the stream specific
state information.
state: The output stream state to release.
*/
typedef void (fz_output_close_fn)(fz_context *ctx, void *state);
This can be as simple as doing fz free(ctx, state), or (depending on the
complexity of the state structure) can require more involved operations to clean
up.
The most important function and the only non-optional one is foo write. This
is a function of type:
/*
fz_output_write_fn: A function type for use when implementing
fz_outputs. The supplied function of this type is called
whenever data is written to the output.
state: The state for the output stream.
data: a pointer to a buffer of data to write.
n: The number of bytes of data to write.
CHAPTER 11. THE OUTPUT INTERFACE 112
*/
typedef void (fz_output_write_fn)(fz_context *ctx, void *state, const
void *data, size_t n);
Optionally we can choose to have our output stream support fz seek output
and fz tell output. To do that we must implement foo seek and foo tell
respectively, and assign them out->seek and out->tell during creation.
/*
fz_output_seek_fn: A function type for use when implementing
fz_outputs. The supplied function of this type is called when
fz_seek_output is requested.
state: The output stream state to seek within.
offset, whence: as defined for fs_seek_output.
*/
typedef void (fz_output_seek_fn)(fz_context *ctx, void *state, fz_off_t
offset, int whence);
/*
fz_output_tell_fn: A function type for use when implementing
fz_outputs. The supplied function of this type is called when
fz_tell_output is requested.
state: The output stream state to report on.
Returns the offset within the output stream.
*/
typedef fz_off_t (fz_output_tell_fn)(fz_context *ctx, void *state);
Chapter 12
Rendered Output Formats
12.1 Overview
MuPDFs built in renderer (see /rjwrefDrawDevice) produces in-memory arrays
of contone values for areas of document pages. The MuPDF library includes
routines to be able to output these areas to a number of different output formats.
Typically these devices all follow a similar pattern, enabling either full page or
banded rendering to be performed according to the requirements of the parti-
cular application.
For a given format XXX, there tend to be 3 functions defined:
void fz_save_pixmap_as_XXX(fz_context *ctx, fz_pixmap *pixmap, char
*filename);
void fz_write_pixmap_as_XXX(fz_context *ctx, fz_output *out, fz_pixmap
*pixmap);
fz_band_writer *fz_new_XXX_band_writer(fz_context *ctx, fz_output *out);
The first function outputs a pixmap to a utf-8 encoded filename as an XXX
formatted file. If the pixmap is not in a suitable colorspace/alpha configuration,
then an exception will be thrown.
The second function does the same thing, but to a given fz output rather than
to a named file.
The third function returns an fz band writer to do the same thing.
113
CHAPTER 12. RENDERED OUTPUT FORMATS 114
12.2 Band Writers
The purpose of the fz band writer mechanism is to allow banded rende-
ring; rather than having to allocate a pixmap large enough to hold the en-
tire page at once, we instead render bands across the page and feed those to
the fz band writer which assembles them into a properly formed XXX format
output stream.
Having created a fz band writer using one of the creation functions defined
in the following sections, the page output starts by calling fz write header.
This both configures the band writer for the type of data that is being sent, and
triggers the output of the file header.
/*
fz_write_header: Cause a band writer to write the header for
a banded image with the given properties/dimensions etc. This
also configures the bandwriter for the format of the data to be
passed in future calls.
w, h: Width and Height of the entire page.
n: Number of components (including alphas).
alpha: Number of alpha components.
xres, yres: X and Y resolutions in dpi.
pagenum: Page number
Throws exception if incompatible data format.
*/
void fz_write_header(fz_context *ctx, fz_band_writer *writer, int w, int
h, int n, int alpha, int xres, int yres, int pagenum);
Next, the caller should render bands of the page in turn, and pass them in to
fz write band.
/*
fz_write_band: Cause a band writer to write the next band
of data for an image.
stride: The byte offset from the first byte of the data
for a pixel to the first byte of the data for the same pixel
on the row below.
band_height: The number of lines in this band.
samples: Pointer to first byte of the data.
*/
CHAPTER 12. RENDERED OUTPUT FORMATS 115
void fz_write_band(fz_context *ctx, fz_band_writer *writer, int stride,
int band_height, const unsigned char *samples);
Once enough data has been sent, the band writer automatically writes any
trailer for the file.
At this point, the caller can either call fz write header to start a new page,
or they can call fz drop band writer to clean up.
void fz_drop_band_writer(fz_context *ctx, fz_band_writer *writer);
12.3 PNM
The simplest output format supported is that of PNM. The pixmap can be
greyscale, or RGB, with or without alpha (though the alpha plane is always
ignored on writing).
/*
fz_save_pixmap_as_pnm: Save a pixmap as a PNM image file.
*/
void fz_save_pixmap_as_pnm(fz_context *ctx, fz_pixmap *pixmap, char
*filename);
void fz_write_pixmap_as_pnm(fz_context *ctx, fz_output *out, fz_pixmap
*pixmap);
fz_band_writer *fz_new_pnm_band_writer(fz_context *ctx, fz_output *out);
12.4 PAM
Related to PNM we have PAM. The pixmap formats here can be greyscale, RGB
or CMYK, with or without alpha (and the alpha plane is written to the file).
The TUPLTYPE in the image header reflects the color and alpha configuration,
though not all readers support all variants.
/*
fz_save_pixmap_as_pam: Save a pixmap as a PAM image file.
*/
void fz_save_pixmap_as_pam(fz_context *ctx, fz_pixmap *pixmap, char
*filename);
void fz_write_pixmap_as_pam(fz_context *ctx, fz_output *out, fz_pixmap
*pixmap);
CHAPTER 12. RENDERED OUTPUT FORMATS 116
fz_band_writer *fz_new_pam_band_writer(fz_context *ctx, fz_output *out);
12.5 PBM
Bitmaps suitable for output to the PBM format are generated by drawing to
greyscale contone (with no alpha), and then halftoning down to monochrome.
/*
fz_save_bitmap_as_pbm: Save a bitmap as a PBM image file.
*/
void fz_save_bitmap_as_pbm(fz_context *ctx, fz_bitmap *bitmap, char
*filename);
void fz_write_bitmap_as_pbm(fz_context *ctx, fz_output *out, fz_bitmap
*bitmap);
fz_band_writer *fz_new_pbm_band_writer(fz_context *ctx, fz_output *out);
12.6 PKM
Bitmaps suitable for output to the PKM format are generated by drawing to
CMYK contone (with no alpha), and then halftoning down to give 1bpc cmyk.
/*
fz_save_bitmap_as_pkm: Save a 4bpp cmyk bitmap as a PAM image file.
*/
void fz_save_bitmap_as_pkm(fz_context *ctx, fz_bitmap *bitmap, char
*filename);
void fz_write_bitmap_as_pkm(fz_context *ctx, fz_output *out, fz_bitmap
*bitmap);
fz_band_writer *fz_new_pkm_band_writer(fz_context *ctx, fz_output *out);
12.7 PNG
The PNG format will accept either greyscale or RGB pixmaps, with or wit-
hout alpha. As a special case, alpha only pixmaps are accepted and written as
greyscale.
/*
CHAPTER 12. RENDERED OUTPUT FORMATS 117
fz_save_pixmap_as_png: Save a pixmap as a PNG image file.
*/
void fz_save_pixmap_as_png(fz_context *ctx, fz_pixmap *pixmap, const
char *filename);
/*
Write a pixmap to an output stream in PNG format.
*/
void fz_write_pixmap_as_png(fz_context *ctx, fz_output *out, const
fz_pixmap *pixmap);
/*
fz_new_png_band_writer: Obtain a fz_band_writer instance
for producing PNG output.
*/
fz_band_writer *fz_new_png_band_writer(fz_context *ctx, fz_output *out);
Because PNG is such a useful and widely used format, we have another couple
of functions. These take either an fz image or an fz pixmap and produce
an fz buffer containing a PNG encoded version. This is very useful when
converting between document formats as we can frequently use a PNG version
of an image as a replacement for other image formats that may not be supported.
/*
Create a new buffer containing the image/pixmap in PNG format.
*/
fz_buffer *fz_new_buffer_from_image_as_png(fz_context *ctx, fz_image
*image);
fz_buffer *fz_new_buffer_from_pixmap_as_png(fz_context *ctx, fz_pixmap
*pixmap);
12.8 PWG/CUPS
The PWG format is intended to encapsulate output for printers. As such there
are many values that can be set in the headers. To allow for this, we expose
these fields as an options structure that can be fed into the output functions.
typedef struct fz_pwg_options_s fz_pwg_options;
struct fz_pwg_options_s
{
/* These are not interpreted as CStrings by the writing code, but
* are rather copied directly out. */
char media_class[64];
char media_color[64];
char media_type[64];
CHAPTER 12. RENDERED OUTPUT FORMATS 118
char output_type[64];
unsigned int advance_distance;
int advance_media;
int collate;
int cut_media;
int duplex;
int insert_sheet;
int jog;
int leading_edge;
int manual_feed;
unsigned int media_position;
unsigned int media_weight;
int mirror_print;
int negative_print;
unsigned int num_copies;
int orientation;
int output_face_up;
unsigned int PageSize[2];
int separations;
int tray_switch;
int tumble;
int media_type_num;
int compression;
unsigned int row_count;
unsigned int row_feed;
unsigned int row_step;
/* These are not interpreted as CStrings by the writing code, but
* are rather copied directly out. */
char rendering_intent[64];
char page_size_name[64];
};
No documentation for these fields is given here - for more information see the
PWG specification.
There are 2 sets of output functions available for PWG, those that take
fz pixmaps (for contone output) and those that take f bitmaps (for halftoned
output).
PWG files are structured as a header (to identify the format), followed by a
stream of pages (images). Those functions that save (or write) a complete file
include the file header as part of their output. If the option is used to append
to a file, then the header is not added, as we presume we are appending new
page information to the end of an existing file.
In circumstances when the header is not output automatically (such as when
using the band writer) the header output must be triggered manually, by calling:
CHAPTER 12. RENDERED OUTPUT FORMATS 119
/*
Output the file header to a pwg stream, ready for pages to follow it.
*/
void fz_write_pwg_file_header(fz_context *ctx, fz_output *out);
12.8.1 Contone
The PWG writer can accept pixmaps in greyscale, RGB and CMYK format,
with no alpha planes.
PWG files can be saved to a file using:
/*
fz_save_pixmap_as_pwg: Save a pixmap as a pwg
filename: The filename to save as (including extension).
append: If non-zero, then append a new page to existing file.
pwg: NULL, or a pointer to an options structure (initialised to zero
before being filled in, for future expansion).
*/
void fz_save_pixmap_as_pwg(fz_context *ctx, fz_pixmap *pixmap, char
*filename, int append, const fz_pwg_options *pwg);
The file header will only be sent in the case where we are not appending to an
existing file.
Alternatively, pages may be sent to an output stream. Two functions exist to
do this. The first always sends a complete PWG file (including header):
/*
Output a pixmap to an output stream as a pwg raster.
*/
void fz_write_pixmap_as_pwg(fz_context *ctx, fz_output *out, const
fz_pixmap *pixmap, const fz_pwg_options *pwg);
The second sends just the page data, and is therefore suitable for sending the
second or subsequent pages in a file. Alternatively, the header can be sent
manually, and then this function can be used for all the pages in a file.
/*
Output a page to a pwg stream to follow a header, or other pages.
*/
void fz_write_pixmap_as_pwg_page(fz_context *ctx, fz_output *out, const
fz_pixmap *pixmap, const fz_pwg_options *pwg);
CHAPTER 12. RENDERED OUTPUT FORMATS 120
Finally, a standard band writer can be used:
/*
fz_new_pwg_band_writer: Generate a new band writer for
contone PWG format images.
*/
fz_band_writer *fz_new_pwg_band_writer(fz_context *ctx, fz_output *out,
const fz_pwg_options *pwg);
In all cases, a NULL value can be sent for the fz pwg options field, in which
case default values will be used.
12.8.2 Mono
The monochrome version of the PWG writer parallels the contone one. It can
accept monochrome bitmaps only.
PWG files can be saved to a file using:
/*
fz_save_bitmap_as_pwg: Save a bitmap as a pwg
filename: The filename to save as (including extension).
append: If non-zero, then append a new page to existing file.
pwg: NULL, or a pointer to an options structure (initialised to zero
before being filled in, for future expansion).
*/
void fz_save_bitmap_as_pwg(fz_context *ctx, fz_bitmap *bitmap, char
*filename, int append, const fz_pwg_options *pwg);
The file header will only be sent in the case where we are not appending to an
existing file.
Alternatively, pages may be sent to an output stream. Two functions exist to
do this. The first always sends a complete PWG file (including header):
/*
Output a bitmap to an output stream as a pwg raster.
*/
void fz_write_bitmap_as_pwg(fz_context *ctx, fz_output *out, const
fz_bitmap *bitmap, const fz_pwg_options *pwg);
The second sends just the page data, and is therefore suitable for sending the
second or subsequent pages in a file. Alternatively, the header can be sent
manually, and then this function can be used for all the pages in a file.
CHAPTER 12. RENDERED OUTPUT FORMATS 121
/*
Output a bitmap page to a pwg stream to follow a header, or other
pages.
*/
void fz_write_bitmap_as_pwg_page(fz_context *ctx, fz_output *out, const
fz_bitmap *bitmap, const fz_pwg_options *pwg);
Finally, a standard band writer can be used:
/*
fz_new_mono_pwg_band_writer: Generate a new band writer for
PWG format images.
*/
fz_band_writer *fz_new_mono_pwg_band_writer(fz_context *ctx, fz_output
*out, const fz_pwg_options *pwg);
In all cases, a NULL value can be sent for the fz pwg options field, in which
case default values will be used.
12.9 TGA
The TGA writer can accept pixmaps in greyscale, RGB and BGR formats, with
and without alpha.
/*
fz_save_pixmap_as_tga: Save a pixmap as a TGA image file.
Can accept RGB, BGR or Grayscale pixmaps, with or without
alpha.
*/
void fz_save_pixmap_as_tga(fz_context *ctx, fz_pixmap *pixmap, const
char *filename);
/*
Write a pixmap to an output stream in TGA format.
Can accept RGB, BGR or Grayscale pixmaps, with or without
alpha.
*/
void fz_write_pixmap_as_tga(fz_context *ctx, fz_output *out, fz_pixmap
*pixmap);
/*
fz_new_tga_band_writer: Generate a new band writer for TGA
format images. Note that image must be generated vertically
flipped for use with this writer!
Can accept RGB, BGR or Grayscale pixmaps, with or without
alpha.
CHAPTER 12. RENDERED OUTPUT FORMATS 122
is_bgr: True, if the image is generated in bgr format.
*/
fz_band_writer *fz_new_tga_band_writer(fz_context *ctx, fz_output *out,
int is_bgr);
12.10 PCL
PCL is not a standard image format, rather it is a page description language for
printers. Unfortunately, the exact implementation of PCL varies from printer
to printer, so it can be necessary to tweak the output according to the exact
intended destination.
Accordingly, we have a pcl options structure to allow this to happen. To use
this, you simply define a pcl options structure on the stack:
pcl_options options = { 0 };
Next you populate those options. Typically this is done by requesting a preset
from our current defined set.
/*
fz_pcl_preset: Retrieve a set of fz_pcl_options suitable for a given
preset.
opts: pointer to options structure to populate.
preset: Preset to fetch. Currently defined presets include:
ljet4 HP DeskJet
dj500 HP DeskJet 500
fs600 Kyocera FS-600
lj HP LaserJet, HP LaserJet Plus
lj2 HP LaserJet IIp, HP LaserJet IId
lj3 HP LaserJet III
lj3d HP LaserJet IIId
lj4 HP LaserJet 4
lj4pl HP LaserJet 4 PL
lj4d HP LaserJet 4d
lp2563b HP 2563B line printer
oce9050 Oce 9050 Line printer
Throws exception on unknown preset.
*/
void fz_pcl_preset(fz_context *ctx, fz_pcl_options *opts, const char
*preset);
CHAPTER 12. RENDERED OUTPUT FORMATS 123
These options can then be tweaked further using fz pcl option:
/*
fz_pcl_option: Set a given PCL option to a given value in the
supplied options structure.
opts: The option structure to modify,
option: The option to change.
val: The value that the option should be set to. Acceptable ranges of
values depend on the option in question.
Throws an exception on attempt to set an unknown option, or an
illegal value.
Currently defined options/values are as follows:
spacing,0 No vertical spacing capability
spacing,1 PCL 3 spacing (<ESC>*p+<n>Y)
spacing,2 PCL 4 spacing (<ESC>*b<n>Y)
spacing,3 PCL 5 spacing (<ESC>*b<n>Y and clear seed
row)
mode2,0 or 1 Disable/Enable mode 2 graphics compression
mode3,0 or 1 Disable/Enable mode 3 graphics compression
mode3,0 or 1 Disable/Enable mode 3 graphics compression
eog_reset,0 or 1 End of graphics (<ESC>*rB) resets all
parameters
has_duplex,0 or 1 Duplex supported (<ESC>&l<duplex>S)
has_papersize,0 or 1 Papersize setting supported
(<ESC>&l<sizecode>A)
has_copies,0 or 1 Number of copies supported
(<ESC>&l<copies>X)
is_ljet4pjl,0 or 1 Disable/Enable HP 4PJL model-specific output
is_oce9050,0 or 1 Disable/Enable Oce 9050 model-specific
output
*/
void fz_pcl_option(fz_context *ctx, fz_pcl_options *opts, const char
*option, int val);
12.10.1 Color
Color PCL output can be generated from RGB pixmaps with alpha (though the
alpha is ignored) using:
void fz_save_pixmap_as_pcl(fz_context *ctx, fz_pixmap *pixmap, char
*filename, int append, const fz_pcl_options *pcl);
CHAPTER 12. RENDERED OUTPUT FORMATS 124
void fz_write_pixmap_as_pcl(fz_context *ctx, fz_output *out, const
fz_pixmap *pixmap, const fz_pcl_options *pcl);
fz_band_writer *fz_new_color_pcl_band_writer(fz_context *ctx, fz_output
*out, const fz_pcl_options *options);
This is 24bpp RGB output, relying on the printers ability to dither. Blank lines
are skipped, repeated lines are coded efficiently, and other lines are coded using
deltas. Nonetheless file sizes can still be large with this output method.
12.10.2 Mono
Monochrome PCL output can be generated from monochrome bitmaps. These
are generated by rendering to greyscale (no alpha) pixmaps and dithering down.
The functions in question are:
fz_band_writer *fz_new_mono_pcl_band_writer(fz_context *ctx, fz_output
*out, const fz_pcl_options *options);
void fz_write_bitmap_as_pcl(fz_context *ctx, fz_output *out, const
fz_bitmap *bitmap, const fz_pcl_options *pcl);
void fz_save_bitmap_as_pcl(fz_context *ctx, fz_bitmap *bitmap, char
*filename, int append, const fz_pcl_options *pcl);
12.11 Postscript
Postscript output is currently done as image output rather than high-level ob-
jects.
Pixmaps suitable for PS image output are greyscale, RGB or CMYK with no
alpha.
void fz_write_pixmap_as_ps(fz_context *ctx, fz_output *out, const
fz_pixmap *pixmap);
void fz_save_pixmap_as_ps(fz_context *ctx, fz_pixmap *pixmap, char
*filename, int append);
fz_band_writer *fz_new_ps_band_writer(fz_context *ctx, fz_output *out);
Postscript requires file level headers and trailers, over and above that produced
by the band writer itself. These can be generated using the following functions:
void fz_write_ps_file_header(fz_context *ctx, fz_output *out);
CHAPTER 12. RENDERED OUTPUT FORMATS 125
void fz_write_ps_file_trailer(fz_context *ctx, fz_output *out, int
pages);
Chapter 13
The Image interface
13.1 Overview
Images are ubiquitous in document formats, and come in a huge variety of
formats, ranging from full colour to monochrome, compressed to uncompressed,
large to small. The ability to efficiently represent and decode 2d arrays of pixels
is vital.
MuPDF represents images using an abstract type, fz image. This takes the
form of a base class, upon which different implementations can be built. All
fz images are reference counted, using the standard fz keep and fz drop con-
ventions:
/*
fz_drop_image: Drop a reference to an image.
image: The image to drop a reference to.
*/
void fz_drop_image(fz_context *ctx, fz_image *image);
/*
fz_keep_image: Increment the reference count of an image.
image: The image to take a reference to.
Returns a pointer to the image.
*/
fz_image *fz_keep_image(fz_context *ctx, fz_image *image);
The key operation required is to be able to request a decoded version of a
subarea of that image (yielding a fz pixmap), suitable for rendering at a given
126
CHAPTER 13. THE IMAGE INTERFACE 127
size:
/*
fz_get_pixmap_from_image: Called to get a handle to a pixmap from an
image.
image: The image to retrieve a pixmap from.
subarea: The subarea of the image that we actually care about (or
NULL
to indicate the whole image).
trans: Optional, unless subarea is given. If given, then on entry
this is
the transform that will be applied to the complete image. It should
be
updated on exit to the transform to apply to the given subarea of the
image. This is used to calculate the desired width/height for
subsampling.
w: If non-NULL, a pointer to an int to be updated on exit to the
width (in pixels) that the scaled output will cover.
h: If non-NULL, a pointer to an int to be updated on exit to the
height (in pixels) that the scaled output will cover.
Returns a non NULL pixmap pointer. May throw exceptions.
*/
fz_pixmap *fz_get_pixmap_from_image(fz_context *ctx, fz_image *image,
const fz_irect *subarea, fz_matrix *trans, int *w, int *h);
Many images have a resolution encoded within them. This may or may not be
honoured in the way they are positioned on the page, and it will certainly not
be honoured when zooming is taken into account, but for some operations it is
useful to be able to request it.
/*
fz_image_resolution: Request the natural resolution
of an image.
xres, yres: Pointers to ints to be updated with the
natural resolution of an image (or a sensible default
if not encoded).
*/
void fz_image_resolution(fz_image *image, int *xres, int *yres);
If no resolution is specified within the image, sensible defaults are returned.
A key ability of fz
images is that they are automatically cached in the fz store
CHAPTER 13. THE IMAGE INTERFACE 128
when decoded - repeated requests for pixmaps from the same image will (not
necessarily) require the image to be decoded again and again.
13.2 Standard Image Types
13.2.1 Compressed
The most common type of fz image is fz compressed image - that is, an image
based upon a fz buffer of data in a standard compressed format, such as JPEG,
PNG, TIFF, and others.
With such images, the data is held in an fz compressed buffer:
typedef struct fz_compressed_buffer_s
{
fz_compression_params params;
fz_buffer *buffer;
} fz_compressed_buffer;
The data is held in the buffer field, and the details of the compression used are
given in the params field, of type fz compression params:
struct fz_compression_params_s
{
int type;
union {
struct {
int color_transform; /* Use -1 for unset */
} jpeg;
struct {
int smask_in_data;
} jpx;
struct {
int columns;
int rows;
int k;
int end_of_line;
int encoded_byte_align;
int end_of_block;
int black_is_1;
int damaged_rows_before_error;
} fax;
struct
{
int columns;
int colors;
int predictor;
CHAPTER 13. THE IMAGE INTERFACE 129
int bpc;
}
flate;
struct
{
int columns;
int colors;
int predictor;
int bpc;
int early_change;
} lzw;
} u;
};
The choice of which of the union clauses is used is made by the type field:
enum
{
FZ_IMAGE_UNKNOWN = 0,
/* Uncompressed samples */
FZ_IMAGE_RAW,
/* Compressed samples */
FZ_IMAGE_FAX,
FZ_IMAGE_FLATE,
FZ_IMAGE_LZW,
FZ_IMAGE_RLD,
/* Full image formats */
FZ_IMAGE_BMP,
FZ_IMAGE_GIF,
FZ_IMAGE_JPEG,
FZ_IMAGE_JPX,
FZ_IMAGE_JXR,
FZ_IMAGE_PNG,
FZ_IMAGE_PNM,
FZ_IMAGE_TIFF,
};
To determine if an fz
image is a compressed image, call:
/*
fz_compressed_image_buffer: Retrieve the underlying compressed
data for an image.
Returns a pointer to the underlying data buffer for an image,
or NULL if this image is not based upon a compressed data
buffer.
CHAPTER 13. THE IMAGE INTERFACE 130
This is not a reference counted structure, so no reference is
returned. Lifespan is limited to that of the image itself.
*/
fz_compressed_buffer *fz_compressed_image_buffer(fz_context *ctx,
fz_image *image);
The easiest way to tell if an image is a compressed image is to request its
underlying buffer. If it returns NULL, you know it is not this sort of image.
13.2.2 Decoded
The next most common type of image is based upon a decoded fz pixmap.
These are generally only used if the pixmap takes less storage than the com-
pressed data would.
/*
fz_pixmap_image_tile: Retried the underlying fz_pixmap
for an image.
Returns a pointer to the underlying fz_pixmap for an image,
or NULL if this image is not based upon an fz_pixmap.
No reference is returned. Lifespan is limited to that of
the image itself. If required, use fz_keep_pixmap to take
a reference to keep it longer.
*/
fz_pixmap *fz_pixmap_image_tile(fz_context *ctx, fz_pixmap_image *cimg);
The easiest way to tell if an image is a decoded image is to request its underlying
tile. If it returns NULL, you know it is not this sort of image.
13.2.3 Display List
The final standard sort of image in MuPDF (though more types may of course
be added in future) is that based upon a display list.
we use this to easily embed one file format within another. For example, epub
files frequently contain SVG images for title pages. We open the SVG image as
a separate document, run it to a display list, and close the document. We can
then create an image from the display list, and use this in the HTML flow of
the epub document.
These images maintain the properties of the original (vector-based) document
in that they remain scalable even after conversion to an image.
CHAPTER 13. THE IMAGE INTERFACE 131
13.3 Creating Images
To create an image from a standard type, simply call the appropriate function.
For example, if you have an fz buffer with the source data:
/*
fz_new_image_from_buffer: Create a new image from a
buffer of data, inferring its type from the format
of the data.
*/
fz_image *fz_new_image_from_buffer(fz_context *ctx, fz_buffer *buffer);
If the data is in a file, use:
/*
fz_image_from_file: Create a new image from the contents
of a file, inferring its type from the format of the
data.
*/
fz_image *fz_new_image_from_file(fz_context *ctx, const char *path);
This loads the data into memory, and calls fz new image from buffer inter-
nally.
If the data cannot be recognised from its header, and more information is requi-
red, then the data can be formed in an fz compressed buffer, and an image
created with:
/*
fz_new_image_from_compressed_buffer: Create an image based on
the data in the supplied compressed buffer.
w,h: Width and height of the created image.
bpc: Bits per component.
colorspace: The colorspace (determines the number of components,
and any color conversions required while decoding).
xres, yres: The X and Y resolutions respectively.
interpolate: 1 if interpolation should be used when decoding
this image, 0 otherwise.
imagemask: 1 if this is an imagemask (i.e. transparent), 0
otherwise.
decode: NULL, or a pointer to to a decode array. The default
decode array is [0 1] (repeated n times, for n color components).
CHAPTER 13. THE IMAGE INTERFACE 132
colorkey: NULL, or a pointer to a colorkey array. The default
colorkey array is [0 255] (repeatd n times, for n color
components).
buffer: Buffer of compressed data and compression parameters.
Ownership of this reference is passed in.
mask: NULL, or another image to use as a mask for this one.
Supplying a masked image as a mask to another image is
illegal!
*/
fz_image *fz_new_image_from_compressed_buffer(fz_context *ctx, int w,
int h, int bpc, fz_colorspace *colorspace, int xres, int yres, int
interpolate, int imagemask, float *decode, int *colorkey,
fz_compressed_buffer *buffer, fz_image *mask);
Finally, if we have a decoded fz pixmap, we can form a new image from it:
/*
fz_new_image_from_pixmap: Create an image from the given
pixmap.
pixmap: The pixmap to base the image upon. A new reference
to this is taken.
mask: NULL, or another image to use as a mask for this one.
A new reference is taken to this image. Supplying a masked
image as a mask to another image is illegal!
*/
fz_image *fz_new_image_from_pixmap(fz_context *ctx, fz_pixmap *pixmap,
fz_image *mask);
13.4 Implementing an Image Type
Support for a new type of image, can be implemented fairly simply, by defining
a structure derived from an fz image, perhaps:
typedef struct
{
fz_image super;
<foo specific fields>
} foo_image;
Then we’d define a new image creation function, fz new image from foo, of the
form:
CHAPTER 13. THE IMAGE INTERFACE 133
fz_image *fz_new_image_from_foo(fz_context *ctx, <foo specific
parameters>) {
foo_image *foo = fz_new_image(ctx, ..., foo_image, foo_get,
foo_size, foo_drop);
if (!foo)
return NULL;
<initialise foo specific fields from foo specific parameters>
return &foo->super;
}
The key call here is the call to fz new image. This is a macro which wraps a
call to fz new image of size:
/*
fz_new_image_of_size: Internal function to make a new fz_image
structure for a derived class.
w,h: Width and height of the created image.
bpc: Bits per component.
colorspace: The colorspace (determines the number of components,
and any color conversions required while decoding).
xres, yres: The X and Y resolutions respectively.
interpolate: 1 if interpolation should be used when decoding
this image, 0 otherwise.
imagemask: 1 if this is an imagemask (i.e. transparent), 0
otherwise.
decode: NULL, or a pointer to to a decode array. The default
decode array is [0 1] (repeated n times, for n color components).
colorkey: NULL, or a pointer to a colorkey array. The default
colorkey array is [0 255] (repeatd n times, for n color
components).
mask: NULL, or another image to use as a mask for this one.
A new reference is taken to this image. Supplying a masked
image as a mask to another image is illegal!
size: The size of the required allocated structure (the size of
the derived structure).
get: The function to be called to obtain a decoded pixmap.
CHAPTER 13. THE IMAGE INTERFACE 134
get_size: The function to be called to return the storage size
used by this image.
drop: The function to be called to dispose of this image once
the last reference is dropped.
Returns a pointer to an allocated structure of the required size,
with the first sizeof(fz_image) bytes initialised as appropriate
given the supplied parameters, and the other bytes set to zero.
*/
fz_image *fz_new_image_of_size(fz_context *ctx, int w, int h, int bpc,
fz_colorspace *colorspace, int xres, int yres, int interpolate, int
imagemask, float *decode, int *colorkey, fz_image *mask, int size,
fz_image_get_pixmap_fn *get, fz_image_get_size_fn *get_size,
fz_drop_image_fn *drop);
#define fz_new_image(CTX,W,H,B,CS,X,Y,I,IM,D,C,M,T,G,S,Z) \
((T*)Memento_label(fz_new_image_of_size(CTX,W,H,B,CS,X,Y,I,IM,D,C,M,sizeof(T),G,S,Z),#T))
The macro takes identical parameters to the function other than passing the
structure type in place of the structure type saved, and performing a typecast
to simplify the typical enclosing code.
Both function and macro take pointers to 3 functions that need to be defined
for the new format. Firstly, foo get is of the following type:
/*
fz_get_pixmap_fn: Function type to get a decoded pixmap
for an image.
im: The image to decode.
subarea: NULL, or the subarea of the image required. Expressed
in terms of a rectangle in the original width/height of the
image. If non NULL, this should be updated by the function to
the actual subarea decoded - which must include the requested
area!
w, h: The actual width and height that the whole image would
need to be decoded to.
l2factor: On entry, the log 2 subsample factor required. If
possible the decode process can take care of (all or some) of
this subsampling, and must then update the value so the caller
knows what remains to be done.
Returns a reference to a decoded pixmap that satisfies the
requirements of the request.
CHAPTER 13. THE IMAGE INTERFACE 135
*/
typedef fz_pixmap *(fz_image_get_pixmap_fn)(fz_context *ctx, fz_image
*im, fz_irect *subarea, int w, int h, int *l2factor);
Secondly, foo get size will be of type:
/*
fz_image_get_size_fn: Function type to get the given storage
size for an image.
Returns the size in bytes used for a given image.
*/
typedef size_t (fz_image_get_size_fn)(fz_context *, fz_image *);
Finally, foo drop will be of type:
/*
fz_drop_image_fn: Function type to destroy an images data
when it’s reference count reaches zero.
*/
typedef void (fz_drop_image_fn)(fz_context *ctx, fz_image *image);
The actual deallocation of the fz image block and its associated resources will
be done on return from this function. The fz drop image fn is responsible
just for deallocating its implementation specific resources (i.e. the contents of
foo image rather than fz image).
13.5 Image Caching
While caching of decoded images happens automatically within MuPDF, it is
perhaps worth saying a small amount about it.
Whenever a decoded image is requested, MuPDF searches in the store (see
chapter 5 Reference Counting, Memory Management and The Store) to see if a
suitable pixmap exists there already. If one is found, the store remembers that
is has been reused, and returned immediately - no decoding is done.
If no suitable pixmap is found, MuPDF calculates how large the image would
be on a rendered page. By comparing this size to the native size of the image,
it calculates a log 2 subsampling factor to use. That is, it attempts to avoid
decoding the image at full size, when one 1/2 (or 1/4 etc) of the width/height
would do.
A log 2 subsampling is used because a) some compression formats such as JPEG
can achieve this as part of their decompression run, and b) it is easy to rapidly
shrink decompressed pixmaps in this way.
CHAPTER 13. THE IMAGE INTERFACE 136
The decoded and subsampled image is then placed into the store so that it will
(hopefully) be found the next time a decode of the image is requested.
Chapter 14
The Document Handler
interface
14.1 Overview
MuPDF is written as an extensible framework for handling different document
types. Each different document format provides an fz document handler struc-
ture that provides the required callbacks to recognise and open files of its sup-
ported type. For example:
extern fz_document_handler pdf_document_handler;
extern fz_document_handler xps_document_handler;
extern fz_document_handler svg_document_handler;
...
At startup, the calling program must register the required document hand-
lers. It can either register them each individually, by repeatedly calling
fz register document handler:
/*
fz_register_document_handler: Register a handler
for a document type.
handler: The handler to register.
*/
void fz_register_document_handler(fz_context *ctx, const
fz_document_handler *handler);
For example:
137
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 138
fz_register_document_handler(ctx, &pdf_document_handler);
fz_register_document_handler(ctx, &xps_document_handler);
fz_register_document_handler(ctx, &svg_document_handler);
...
or, it can use a convenience function to register all the standard handlers enabled
in a given build:
/*
fz_register_document_handler: Register handlers
for all the standard document types supported in
this build.
*/
void fz_register_document_handlers(fz_context *ctx);
14.2 Implementing a Document Handler
14.2.1 Recognize and Open
To implement a new document handler, a new fz document handler structure
is required. There are 3 components to such a structure, all function pointers:
typedef struct fz_document_handler_s
{
fz_document_recognize_fn *recognize;
fz_document_open_fn *open;
fz_document_open_with_stream_fn *open_with_stream;
} fz_document_handler;
The first is a function to recognize a document from a magic string, typically a
mimetype or a filename:
/*
fz_document_recognize_fn: Recognize a document type from
a magic string.
magic: string to recognise - typically a filename or mime
type.
Returns a number between 0 (not recognized) and 100
(fully recognized) based on how certain the recognizer
is that this is of the required type.
*/
typedef int (fz_document_recognize_fn)(fz_context *ctx, const char
*magic);
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 139
The second is a function to open a document from a filename:
/*
fz_document_open_fn: Function type to open a document from a
file.
filename: file to open
Pointer to opened document. Throws exception in case of error.
*/
typedef fz_document *(fz_document_open_fn)(fz_context *ctx, const char
*filename);
This function can permissibly be NULL, as it can be synthesized automatically
from the third entry, a function to open a document from a stream:
/*
fz_document_open_with_stream_fn: Function type to open a
document from a file.
stream: fz_stream to read document data from. Must be
seekable for formats that require it.
Pointer to opened document. Throws exception in case of error.
*/
typedef fz_document *(fz_document_open_with_stream_fn)(fz_context *ctx,
fz_stream *stream);
To create an fz document use the fz new document macro. For a document of
type foo, typically a foo document structure would be defined as below:
typedef struct
{
fz_document super;
<foo specific fields>
} foo_document;
This would then be created using a call to fz new document, such as:
foo_document *foo = fz_new_document(ctx, foo_document);
This returns an empty document structure with super populated with default
values, and the foo specific fields initialized to 0. The document handler then
needs to fill in the document level functions.
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 140
14.2.2 Document Level Functions
The fz document structure contains a list of functions used to implement the
document level calls:
typedef struct fz_document_s
{
int refs;
fz_document_drop_fn *drop_document;
fz_document_needs_password_fn *needs_password;
fz_document_authenticate_password_fn *authenticate_password;
fz_document_has_permission_fn *has_permission;
fz_document_load_outline_fn *load_outline;
fz_document_layout_fn *layout;
fz_document_make_bookmark_fn *make_bookmark;
fz_document_lookup_bookmark_fn *lookup_bookmark;
fz_document_resolve_link_fn *resolve_link;
fz_document_count_pages_fn *count_pages;
fz_document_load_page_fn *load_page;
fz_document_lookup_metadata_fn *lookup_metadata;
int did_layout;
int is_reflowable;
} fz_document;
Implementations must fill in the drop document field, with a pointer to a
function called to free any resources help by the document when the reference
count drops to 0. In the unlikely event that your implementation has no resour-
ces, this field can be left NULL.
/*
fz_document_drop_fn: Called when the reference count for
the fz_document drops to 0. The implementation should
release any resources held by the document. The actual
document pointer will be freed by the caller.
*/
typedef void (fz_document_drop_fn)(fz_context *ctx, fz_document *doc);
If your document handler is capable of handling password protected documents,
then you must fill in the needs password field with a pointer to a function called
to enquire whether a given document needs a password:
/*
fz_document_needs_password_fn: Type for a function to be
called to enquire whether the document needs a password
or not. See fz_needs_password for more information.
*/
typedef int (fz_document_needs_password_fn)(fz_context *ctx, fz_document
*doc);
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 141
If your document handler is capable of handling password protected documents,
then you must fill in the authenticate password field with a pointer to a
function called to attempt to authenticate a password:
/*
fz_document_authenticate_password_fn: Type for a function to be
called to attempt to authenticate a password. See
fz_authenticate_password for more information.
*/
typedef int (fz_document_authenticate_password_fn)(fz_context *ctx,
fz_document *doc, const char *password);
Certain document types encode permissions within them to say what users are
allowed to do with them (printing, extracting etc). If your document handler’s
format has this concept, then you must fill in the has permission field with a
pointer to a function called to attempt to query such permissions:
/*
fz_document_has_permission_fn: Type for a function to be
called to see if a document grants a certain permission. See
fz_document_has_permission for more information.
*/
typedef int (fz_document_has_permission_fn)(fz_context *ctx, fz_document
*doc, fz_permission permission);
Certain document types can optionally include outline (table of contents) infor-
mation within them. If your document handler’s format has this concept, then
you must fill in the load outline field with a pointer to a function called to
attempt to load such information if it is there:
/*
fz_document_load_outline_fn: Type for a function to be called to
load the outlines for a document. See fz_document_load_outline
for more information.
*/
typedef fz_outline *(fz_document_load_outline_fn)(fz_context *ctx,
fz_document *doc);
If your document format requires a layout pass before it can be viewed, then
you must fill in the layout field with a pointer to a function called to perform
such a layout:
/*
fz_document_layout_fn: Type for a function to be called to lay
out a document. See fz_layout_document for more information.
*/
typedef void (fz_document_layout_fn)(fz_context *ctx, fz_document *doc,
float w, float h, float em);
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 142
If your document requires a layout pass, you should provide functions to both
make and resolve bookmarks to enable reader positions to be kept over layout
changes. Accordingly the make bookmark and lookup bookmark fields should
be filled out:
/*
fz_document_make_bookmark_fn: Type for a function to make
a bookmark. See fz_make_bookmark for more information.
*/
typedef fz_bookmark (fz_document_make_bookmark_fn)(fz_context *ctx,
fz_document *doc, int page);
/*
fz_document_lookup_bookmark_fn: Type for a function to lookup
a bookmark. See fz_lookup_bookmark for more information.
*/
typedef int (fz_document_lookup_bookmark_fn)(fz_context *ctx,
fz_document *doc, fz_bookmark mark);
Some document formats can encode internal links that point to another page
in the document. If your document supports this concept, then you must fill in
the resolve link field with a pointer to a function called to resolve a textual
link to a page number, and location on that page:
/*
fz_document_resolve_link_fn: Type for a function to be called to
resolve an internal link to a page number. See fz_resolve_link
for more information.
*/
typedef int (fz_document_resolve_link_fn)(fz_context *ctx, fz_document
*doc, const char *uri, float *xp, float *yp);
All document formats must fill in the count pages field with a pointer to a
function called to return the number of pages in a document:
/*
fz_document_count_pages_fn: Type for a function to be called to
count the number of pages in a document. See fz_count_pages for
more information.
*/
typedef int (fz_document_count_pages_fn)(fz_context *ctx, fz_document
*doc);
Different document formats encode different types of metadata. We therefore
have an extensible function to allow such data to be queried. If your document
handler wishes to support this, then the lookup metadata field must be filled
in with a pointer to a function to perform such lookups:
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 143
/*
fz_document_lookup_metadata_fn: Type for a function to query
a documents metadata. See fz_lookup_metadata for more
information.
*/
typedef int (fz_document_lookup_metadata_fn)(fz_context *ctx,
fz_document *doc, const char *key, char *buf, int size);
All document formats must fill in the load page field with a pointer to a function
called to return a reference to a fz page structure:
/*
fz_document_load_page_fn: Type for a function to load a given
page from a document. See fz_load_page for more information.
*/
typedef fz_page *(fz_document_load_page_fn)(fz_context *ctx, fz_document
*doc, int number);
To create a fz page use the fz new page macro. For a document of type foo,
typically a foo page structure would be defined as below:
typedef struct
{
fz_page super;
<foo specific fields>
} foo_page;
This would then be created using a call to fz new page, such as:
foo_page *foo = fz_new_page(ctx, foo_page);
This returns an empty document structure with super populated with default
values, and the foo specific fields initialized to 0. The document handler imple-
mentation then needs to fill in the page level functions.
14.2.3 Page Level Functions
The fz page structure contains a list of functions used to implement the page
level calls:
typedef struct fz_page_s
{
int refs;
fz_page_drop_page_fn *drop_page;
fz_page_bound_page_fn *bound_page;
fz_page_run_page_contents_fn *run_page_contents;
fz_page_load_links_fn *load_links;
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 144
fz_page_first_annot_fn *first_annot;
fz_page_page_presentation_fn *page_presentation;
fz_page_control_separation_fn *control_separation;
fz_page_separation_disabled_fn *separation_disabled;
fz_page_count_separations_fn *count_separations;
fz_page_get_separation_fn *get_separation;
} fz_page;
The fz page (and hence derived foo page) structures are reference counted.
The refs field is used to keep the reference count in. All the reference counting
is handled by the core library, and all that is required of the implementation is
that it should supply a drop page function that will be called when the reference
count reaches zero. This is of type:
/*
fz_page_drop_page_fn: Type for a function to release all the
resources held by a page. Called automatically when the
reference count for that page reaches zero.
*/
typedef void (fz_page_drop_page_fn)(fz_context *ctx, fz_page *page);
Implementations must fill in the bound page field with the address of a function
to return the pages bounding box, of type:
/*
fz_page_bound_page_fn: Type for a function to return the
bounding box of a page. See fz_bound_page for more
information.
*/
typedef fz_rect *(fz_page_bound_page_fn)(fz_context *ctx, fz_page *page,
fz_rect *);
Implementations must fill in the run page contents field with the address of a
function to interpret the contents of a page, of type:
/*
fz_page_run_page_contents_fn: Type for a function to run the
contents of a page. See fz_run_page_contents for more
information.
*/
typedef void (fz_page_run_page_contents_fn)(fz_context *ctx, fz_page
*page, fz_device *dev, const fz_matrix *transform, fz_cookie
*cookie);
If a document format supports internal or external hyperlinks, then its imple-
mentation must fill in the load links field with the address of a function to
load the links from a page, of type:
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 145
/*
fz_page_load_links_fn: Type for a function to load the links
from a page. See fz_load_links for more information.
*/
typedef fz_link *(fz_page_load_links_fn)(fz_context *ctx, fz_page *page);
If a document format supports annotations, then its implementation must fill
in the first annot field with the address of a function to load the annotations
from a page, of type:
/*
fz_page_first_annot_fn: Type for a function to load the
annotations from a page. See fz_first_annot for more
information.
*/
typedef fz_annot *(fz_page_first_annot_fn)(fz_context *ctx, fz_page
*page);
Some document formats can encode information that specifies how pages should
be presented to the user as a slideshow - how long they should be displayed, and
which transition to use when moving to the next page etc. In implementations of
document handlers for such formats, they should fill in the page presentation
field with the address of a function to obtain this information, of type:
/*
fz_page_page_presentation_fn: Type for a function to
obtain the details of how this page should be presented when
in presentation mode. See fz_page_presentation for more
information.
*/
typedef fz_transition *(fz_page_page_presentation_fn)(fz_context *ctx,
fz_page *page, fz_transition *transition, float *duration);
Some document formats can encapsulate multiple color separations. In or-
der to allow proofing of such formats, MuPDF allows such separations to be
enumerated and enabled/disabled. In document handlers for such document
formats, the control separation, separation disabled, count separations
and get separation fields should be filled in with functions of the following ty-
pes respectively:
/*
fz_page_control_separation: Type for a function to enable/
disable separations on a page. See fz_control_separation for
more information.
*/
typedef void (fz_page_control_separation_fn)(fz_context *ctx, fz_page
*page, int separation, int disable);
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 146
/*
fz_page_separation_disabled_fn: Type for a function to detect
whether a given separation is enabled or disabled on a page.
See fz_separation_disabled for more information.
*/
typedef int (fz_page_separation_disabled_fn)(fz_context *ctx, fz_page
*page, int separation);
/*
fz_page_count_separations_fn: Type for a function to count
the number of separations on a page. See fz_count_separations
for more information.
*/
typedef int (fz_page_count_separations_fn)(fz_context *ctx, fz_page
*page);
/*
fz_page_get_separation_fn: Type for a function to retrieve
details of a separation on a page. See fz_get_separation
for more information.
*/
typedef const char *(fz_page_get_separation_fn)(fz_context *ctx, fz_page
*page, int separation, uint32_t *rgb, uint32_t *cmyk);
14.3 Standard Document Handlers
MuPDF contains a range of document handlers for different formats. Which
of these are built/enabled by default depends on configuration options in the
include/mupdf/fitz/config.h file. See chapter 18 Build configuration for
more information.
14.3.1 PDF
Support for PDF (Portable Document Format) is provided by
pdf document handler. All current versions at the time of writing (i.e
up to and including PDF 1.7) are supported.
MuPDF contains functionality to allow deeper access to the contents and struc-
ture of a PDF file than is exposed through the standard fz prefixed functions,
by using pdf prefixed functions.
The library provides a pdf specifics function to safely promote a fz document
pointer to a pdf document pointer. This will return NULL if the document is
not a PDF, indicating that the pdf functions cannot be used.
CHAPTER 14. THE DOCUMENT HANDLER INTERFACE 147
14.3.2 XPS
Support for XPS (Open XML Paper Specification) is provided by
xps document handler. All current versions at the time of writing are sup-
ported.
14.3.3 EPUB
Support for EPub v2 is provided by epub document handler. Tables are not
currently supported, but is planned. Support for v3 is not planned.
The same document handler supports the FB2 (Fiction Book 2) electronic book
format.
14.3.4 HTML
Support for basic HTML + simple CSS is provided by
htdoc document handler. Tables are not currently supported, but is
planned.
14.3.5 SVG
Support for SVG (Scalable Vector Graphics) is provided by
svg document handler. Support is incomplete, but sufficient for many
files.
14.3.6 Image
Support for a range of common image types (including PNG, JPEG, TIFF,
JPEG2000, BMP and GIF) is provided by image document handler.
14.3.7 CBZ
Support for CBZ (Comic Book Archive) format is provided by
cbz document handler. This supports files in .zip or .tar format.
Chapter 15
The Document Writer
interface
15.1 Usage
As well as opening existing documents, MuPDF contains functions to allow the
easy creation of new documents. The most general form of this functionality
takes the form of the fz document writer interface.
A document writer is obtained by calling a generation function. The most
general purpose one is:
/*
fz_new_document_writer: Create a new fz_document_writer, for a
file of the given type.
path: The document name to write (or NULL for default)
format: Which format to write (currently cbz, pdf, pam, pbm,
pgm, pkm, png, ppm, pnm, svg, tga)
options: NULL, or pointer to comma separated string to control
file generation.
*/
fz_document_writer *fz_new_document_writer(fz_context *ctx, const char
*path, const char *format, const char *options);
Alternatively, direct calls to generate specific document writers can be used,
such as:
fz_document_writer *fz_new_cbz_writer(fz_context *ctx, const char *path,
148
CHAPTER 15. THE DOCUMENT WRITER INTERFACE 149
const char *options);
fz_document_writer *fz_new_pdf_writer(fz_context *ctx, const char *path,
const char *options);
fz_document_writer *fz_new_svg_writer(fz_context *ctx, const char *path,
const char *options);
fz_document_writer *fz_new_png_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_tga_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_pam_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_pnm_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_pgm_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_ppm_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_pbm_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
fz_document_writer *fz_new_pkm_pixmap_writer(fz_context *ctx, const char
*path, const char *options);
Once a fz document writer has been created, pages can be written to the
document one at a time. The process is started by calling fz begin page:
/*
fz_begin_page: Called to start the process of writing a page to
a document.
mediabox: page size rectangle in points.
Returns a fz_device to write page contents to.
*/
fz_device *fz_begin_page(fz_context *ctx, fz_document_writer *wri, const
fz_rect *mediabox);
This function returns a fz device pointer that should be used to write the
page contents to. This can be done by making a sequence of normal device calls
(see chapter 7 The Device interface) to paint the page with its content. One
of the most common ways of doing this is by calling fz run page contents on
another open document. This therefore offers a quick mechanism for converting
documents from one format to another.
Once the page contents have all been written, the page is finalized by calling
fz end page:
/*
fz_end_page: Called to end the process of writing a page to a
document.
CHAPTER 15. THE DOCUMENT WRITER INTERFACE 150
*/
void fz_end_page(fz_context *ctx, fz_document_writer *wri);
At this point, many formats will allow more pages to be written, simply by
repeating the fz begin page, output, fz end page loop.
When all the pages have been written, the produced document can be finalized
by calling fz close document writer:
/*
fz_close_document_writer: Called to end the process of writing
pages to a document.
This writes any file level trailers required. After this
completes successfully the file is up to date and complete.
*/
void fz_close_document_writer(fz_context *ctx, fz_document_writer *wri);
Finally, the document writer itself can be freed in the usual fashion by calling
fz drop document writer:
/*
fz_drop_document_writer: Called to discard a fz_document_writer.
This may be called at any time during the process to release all
the resources owned by the writer.
Calling drop without having previously called drop may leave
the file in an inconsistent state.
*/
void fz_drop_document_writer(fz_context *ctx, fz_document_writer *wri);
15.2 Implementation
Support for a new type of document writer requires a new structure, derived
from fz document writer:
typedef struct
{
fz_document_writer_begin_page_fn *begin_page;
fz_document_writer_end_page_fn *end_page;
fz_document_writer_close_writer_fn *close_writer;
fz_document_writer_drop_writer_fn *drop_writer;
fz_device *dev;
} fz_document_writer;
For instance:
CHAPTER 15. THE DOCUMENT WRITER INTERFACE 151
typedef struct
{
fz_document_writer super;
<foo specific fields>
} foo_document_writer;
A generator function should be defined to return such an instance, perhaps:
fz_document_writer *fz_new_foo_document_writer(fz_context *ctx, const
char *path, <foo specific params>) {
foo_document_writer *foo = fz_new_derived_document_writer(ctx,
foo_document_writer, foo_begin_page, foo_end_page, foo_close,
foo_drop);
<initialise foo specific fields>
return &foo->super;
}
This uses a friendly macro that allocates a structure of the required size, ini-
tialises the function pointers as required, and zeroes the extra values in the
structure.
/*
fz_new_document_writer_of_size: Internal function to allocate a
block for a derived document_writer structure, with the base
structure’s function pointers populated correctly, and the extra
space zero initialised.
*/
fz_document_writer *fz_new_document_writer_of_size(fz_context *ctx,
size_t size, fz_document_writer_begin_page_fn *begin_page,
fz_document_writer_end_page_fn *end_page,
fz_document_writer_close_writer_fn *close,
fz_document_writer_drop_writer_fn *drop);
#define
fz_new_derived_document_writer(CTX,TYPE,BEGIN_PAGE,END_PAGE,CLOSE,DROP)
\
((TYPE
*)Memento_label(fz_new_document_writer_of_size(CTX,sizeof(TYPE),BEGIN_PAGE,END_PAGE,CLOSE,DROP),#TYPE))
The actual work for the document writer is done in the functions that are pas-
sed to fz new derived document writer. In the example above these were
foo begin page, foo end page, foo close, and foo drop. These have the fol-
lowing 4 types respectively.
/*
fz_document_writer_begin_page_fn: Function type to start
the process of writing a page to a document.
CHAPTER 15. THE DOCUMENT WRITER INTERFACE 152
mediabox: page size rectangle in points.
Returns a fz_device to write page contents to.
*/
typedef fz_device *(fz_document_writer_begin_page_fn)(fz_context *ctx,
fz_document_writer *wri, const fz_rect *mediabox);
/*
fz_document_writer_end_page_fn: Function type to end the
process of writing a page to a document.
dev: The device created by the begin_page function.
*/
typedef void (fz_document_writer_end_page_fn)(fz_context *ctx,
fz_document_writer *wri, fz_device *dev);
/*
fz_document_writer_close_writer_fn: Function type to end
the process of writing pages to a document.
This writes any file level trailers required. After this
completes successfully the file is up to date and complete.
*/
typedef void (fz_document_writer_close_writer_fn)(fz_context *ctx,
fz_document_writer *wri);
/*
fz_document_writer_drop_writer_fn: Function type to discard
an fz_document_writer. This may be called at any time during
the process to release all the resources owned by the writer.
Calling drop without having previously called close may leave
the file in an inconsistent state.
*/
typedef void (fz_document_writer_drop_writer_fn)(fz_context *ctx,
fz_document_writer *wri);
Once defined, if this is intended to be a generally useful document writer, it
should probably be hooked into fz new document writer, where it can be se-
lected by appropriate format and options strings.
Chapter 16
Progressive Mode
16.1 Overview
When used in the normal way, MuPDF requires the entirety of a file to be
present before it can be opened. For some applications, this can be a significant
restriction - for instance, when downloading a PDF file over a slow internet link,
being able to view just the first page or two may be enough to know whether it
is the correct file or not.
Normal PDF files require the end of the file to be present before file reading can
begin, as this is where the ‘trailer’ lives (effectively the index for the entire file).
In an effort to allow early display of the first page, Adobe (the originators of the
PDF format) introduced the concept of a ‘linearized’ PDF file. This is a PDF
file that, while constructed in accordance with the original specification, also
has some extra information contained within the file to allow fast access to the
first page. This information is known as the ‘hint stream’. In addition, extra
constraints are placed upon the ordering of data within the file in an effort to
ensure that the first page will download quickly.
Unfortunately, Linearized PDF files are far from a panacea. The specification
is overly-complex, unclear and consequently poorly supported in both readers
and writers of the format. Even when implemented correctly, it is of limited use
for pages other than the first one.
MuPDF therefore attempts to solve the problem using a combination of mecha-
nisms, known together as “progressive mode”. When run in this mode, MuPDF
can not only take advantage of the linearization information (if present) in a
file, but is also capable of directing the actual download mechanism used by a
file. By controlling the order in which sections of a file are fetched, any page
required can be viewed before the whole fetch is complete.
153
CHAPTER 16. PROGRESSIVE MODE 154
For optimum performance a file should be both linearized and be available over
a byte-range supporting link, but benefits can still be had with either one of
these alone.
Coupled with the ability to render pages ignoring (and detecting) errors, this
means that ‘rough renderings’ of pages can be given even before all the content
(such as images and fonts) for a page have been downloaded.
16.2 Implementation
MuPDF has made various extensions to its mechanisms for handling progressive
loading. They rely on some special properties built into a type of fz stream
known as a ‘progressive’ stream.
16.2.1 Progressive Streams
At its lowest level MuPDF reads file data from a fz stream, using
the fz open document with stream call. The alternative entrypoint
fz open document is implemented by calling this.
The PDF interpreter uses the fz lookup metadata call to check for its stream
being progressive or not. Any non-progressive stream will be read as normal,
with the system assuming that the entire file is present immediately.
If it is found to be progressive, another fz lookup metadata call is made to
find out what the length of the stream will be once the entire file is fetched. An
HTTP fetcher can know this by consulting the Content-Length header before
any data has been fetched.
With this information MuPDF can decide whether a file is linearized or not.
(Technically, knowing the length enables us to check with the length value given
in a linearized object - if these differ, the assumption is that an incremental save
has taken place, thus the file is no longer linearized.)
Other than supporting the required metadata responses, the key thing that
marks a stream as being progressive, is that it will not block when attempting
to read data it does not have. Instead, it will throw a FZ ERROR TRYLATER error.
This particular error code will be interpreted by the caller as an indication that
it should retry the parsing of the current objects at a later time.
When a MuPDF call is made on a progressive stream, such as
fz open document with stream, or fz load page, the caller should be prepa-
red to handle a FZ ERROR TRYLATER error as meaning that more data is required
before it can continue. No indication is directly given as to exactly how much
more data is required, but as the caller will be implementing the progressive
CHAPTER 16. PROGRESSIVE MODE 155
fz stream that it has passed into MuPDF to start with, it can reasonably be
expected to figure out an estimate for itself.
With these mechanisms in place, a caller can repeatedly try to render each page
in turn until it gets a successful result.
16.2.2 Rough renderings
Once a page has been loaded, if its contents are to be ‘run’ as normal (using
e.g. fz run page) any error (such as failing to read a font, or an image, or
even a content stream belonging to the page) will result in a rendering that
aborts with an FZ ERROR TRYLATER error. The caller can catch this and display
a placeholder instead.
If each pages data was entirely self-contained and sent in sequence this would
perhaps be acceptable, with each page appearing one after the other. Unfortu-
nately, the linearization procedure as laid down by Adobe does NOT do this:
objects shared between multiple pages (other than the first) are not sent with
the pages themselves, but rather AFTER all the pages have been sent.
This means that a document that has a title page, then contents that share a
font used on pages 2 onwards, will not be able to correctly display page 2 until
after the font has arrived in the file, which will not be until all the page data
has been sent.
To mitigate against this, MuPDF provides a way whereby callers can indicate
that they are prepared to accept an ‘incomplete’ rendering of the file (perhaps
with missing images, or with substitute fonts).
Callers prepared to tolerate such renderings should set the ‘incomplete ok’ flag
in the cookie, then call fz run page etc as normal. If a FZ ERROR TRYLATER error
is thrown at any point during the page rendering, the error will be swallowed,
the ‘incomplete’ field in the cookie will become non-zero and rendering will
continue. When control returns to the caller the caller can check the value of the
‘incomplete’ field and know that the rendering it received is not authoritative.
16.2.3 Directed downloads
If the caller has control over the fetch of the file (be it http or some other
protocol), then it is possible to use byte range requests to fetch the document
‘out of order’. This enables non-linearized files to be progressively displayed
as they download, and fetches complete renderings of pages earlier than would
otherwise be the case. This process requires no changes within MuPDF itself,
but rather in the way the progressive stream learns from the attempts MuPDF
makes to fetch data.
Consider for example, an attempt to fetch a hypothetical file from a server.
CHAPTER 16. PROGRESSIVE MODE 156
• The initial http request for the document is sent with a “Range:” header
to pull down the first (say) 4k of the file.
• As soon as we get the header in from this initial request, we can respond
to meta stream operations to give the length, and whether byte requests
are accepted.
– If the header indicates that byte ranges are acceptable the stream
proceeds to go into a loop fetching chunks of the file at a time (not
necessarily in-order). Otherwise the server will ignore the Range:
header, and just serve the whole file.
– If the header indicates a content-length, the stream returns that.
• MuPDF can then decide how to proceed based upon these flags and whet-
her the file is linearized or not. (If the file contains a linearized object,
and the content length matches, then the file is considered to be linear,
otherwise it is not).
If the file is linear:
– We proceed to read objects out of the file as it downloads. This will
provide us the first page and all its resources. It will also enable us
to read the hint streams (if present).
– Once we have read the hint streams, we unpack (and sanity check)
them to give us a map of where in the file each object is predicted
to live, and which objects are required for each page. If any of these
values are out of range, we treat the file as if there were no hint
streams.
– If we have hints, any attempt to load a subsequent page will cause
MuPDF to attempt to read exactly the objects required. This will
cause a sequence of seeks in the fz
stream followed by reads. If
the stream does not have the data to satisfy that request yet, the
stream code should remember the location that was fetched (and
fetch that block in the background so that future retries will succeed)
and should raise an FZ ERROR TRYLATER error.
[Typically therefore when we jump to a page in a linear file on a byte
request capable link, we will quickly see a rough rendering, which
will improve fairly fast as images and fonts arrive.]
– Regardless of whether we have hints or byte requests, on every
fz load page call MuPDF will attempt to process more of the stream
(that is assumed to be being downloaded in the background). As line-
arized files are guaranteed to have pages in order, pages will gradually
become available. In the absence of byte requests and hints however,
we have no way of getting resources early, so the renderings for these
pages will remain incomplete until much more of the file has arrived.
CHAPTER 16. PROGRESSIVE MODE 157
[Typically therefore when we jump to a page in a linear file on a non
byte request capable link, we will see a rough rendering for that page
as soon as data arrives for it (which will typically take much longer
than would be the case with byte range capable downloads), and that
will improve much more slowly as images and fonts may not appear
until almost the whole file has arrived.]
– When the whole file has arrived, then we will attempt to read the
outlines for the file.
For a non-linearized PDF on a byte request capable stream:
– MuPDF will immediately seek to the end of the file to attempt to
read the trailer. This will fail with a FZ ERROR TRYLATER due to the
data not being here yet, but the stream code should remember that
this data is required and it should be prioritized in the background
fetch process.
– Repeated attempts to open the stream should eventually succeed
therefore. As MuPDF jumps through the file trying to read first the
xrefs, then the page tree objects, then the page contents themselves
etc, the background fetching process will be driven by the attempts
to read the file in the foreground.
[Typically therefore the opening of a non-linearized file will be slower than
a linearized one, as the xrefs/page trees for a non-linear file can be 20%+
of the file data. Once past this initial point however, pages and data can
be pulled from the file almost as fast as with a linearized file.]
For a non-linearized PDF on a non-byte request capable stream:
– MuPDF will immediately seek to the end of the file to attempt to
read the trailer. This will fail with a FZ ERROR TRYLATER due to the
data not being here yet. Subsequent retries will continue to fail until
the whole file has arrived, whereupon the whole file will be instantly
available.
[This is the worst case situation - nothing at all can be displayed until the
entire file has downloaded.]
16.2.4 Example implementation
An example implementation of a fetcher process can be found in curl-stream.c.
This implements a fz stream using the popular ‘curl’ http fetching library.
The structure of this process broadly behaves as follows:
• We consider the file as an (initially empty) buffer which we are filling by
making requests. In order to ensure that we make maximum use of our do-
wnload link, we ensure that whenever one request finishes, we immediately
CHAPTER 16. PROGRESSIVE MODE 158
launch another. Further, to avoid the overheads for the request/response
headers being too large, we may want to divide the file into ‘chunks’,
perhaps 4 or 32k in size.
• We have a receiver thread that sits there in a loop requesting chunks to fill
this buffer. In the absence of any other impetus the receiver should request
the next chunk of data from the file that it does not yet have, following the
last fill point. Initially we start the fill point at the beginning of the file,
but this will move around based on the requests made of the progressive
stream.
• Whenever MuPDF attempts to read from the stream, we check to see if
we have data for this area of the file already. If we do, we can return it. If
not, we remember this as the next ‘fill point’ for our receiver process and
throw a FZ ERROR TRYLATER error.
• The caller process is responsible for implementing the fetcher, hence it can
know when more data has arrived. This can trigger retries of renderings
intelligently, thus avoiding retrying renders when the incoming data is
stalled.
Chapter 17
Fonts
159
Chapter 18
Build configuration
160
Chapter 19
PDF Page Manipulation
161
Chapter 20
PDF Interpreter Details
20.1 PDF Document
20.2 PDF Objects
20.3 PDF Operator Processors
20.3.1 Run processor
20.3.2 Filter processor
20.3.3 Buffer processor
162
Chapter 21
XPS Interpreter Details
163
Chapter 22
EPub Interpreter Details
164
Chapter 23
SVG Interpreter Details
165
Chapter 24
MuTool
24.1 Overview
24.2 Clean
24.3 Create
24.4 Draw
24.5 Extract
24.6 Info
24.7 Merge
24.8 Pages
24.9 Poster
24.10 Show
166
Chapter 25
Platform specifics
25.1 Android viewer
25.2 Desktop Java
25.2.1 Language bindings
25.2.2 Viewer
25.3 GSView
25.4 Javascript
25.5 Linux/Windows viewer
25.5.1 Non-GL version
25.5.2 GLFW version
167
Appendix A
Naming conventions and
style
168
