[gs-devel] Re: ghostscript vector devices

[Behdad Esfahbod]

Thanks Ralph,

I'm subscribed to the gs-devel list now.  I started reading ghostscript
docs and learned most of the stuff you wrote, though I was starting from
gdevps.c.  Rebasing to gdevpx stuff now.

I'm impressed by the garbage collection implementation in ghostscript.
Very nice indeed.  But yeah, ugly, like all other OOP C implementations.

Thanks again, will keep you posted.

behdad

On Tue, 2007-10-02 at 18:17 -0700, Ralph Giles wrote:
> Behdad,
> 
> You asked about where to start with a ghostscript output layer using 
> cairo, but we didn't get a chance to go over the details. Here's mostly 
> what I said, but in writing. :)
> 
> Output back-ends in Ghostscript are called "devices". See 
> http://ghostscript.com/doc/current/Drivers.htm#Structure
> for general life cycle information.
> 
> To do a vector output device you want to subclass gx_device_vector,
> which provides an callback vector for when any of the path stuff
> changes, which I think will be a good match for cairo's immediate
> mode api.
> 
> The class is in gdevvec.h, reading the implementation in gdevvec.c will 
> be necessary on some points to get the calling convention right. The 
> simplest device to start cloning is the pxlcolor device (gdevpx*). The 
> most sophisticated is the pdfwrite device. You'll ultimately have to 
> look there for how to do fonts, etc.
> 
> Probably a lot of the pdfwrite stuff could be moved into 
> gx_device_vector or an intermediate class if it ends up
> being shared. Ken's the one to talk about that (later).
> 
> Some general notes on the gs source. Like all object oriented
> programming in C schemes, it's a bit messy. Objects are structs,
> "inheritance" is done by using macros to define the struct fields
> the class, which is the used to instantiate the same fields at
> the head of the struct defining any subclasses, so casting works.
> All pointer fields are enumerated in a special struct so the 
> garbage collector can update them after object relocation. Strings
> and few other things are special cased.
> 
> Good luck, and let us know if you have any questions. I'd really
> like to see a gdevcairo!
> 
> Cheers,
>  -r
-- 
behdad
http://behdad.org/

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