[gs-devel] Asking for a application oriented API for libgs

[Albert Astals Cid]

Sorry for the late reply, i've been very busy this week.

A Divendres 06 Juliol 2007, Ralph Giles va escriure:
> On Fri, Jul 06, 2007 at 06:25:26PM +0200, Albert Astals Cid wrote:
> > Hi, i am one of the KDE[1] people working on okular[2], the KDE4 document
> > viewer.
>
> Cool.
>
> > The problem is that libgs API [3] is much more oriented to writing a ps
> > interpreter than oriented to what a viewer application needs. Or at least
> > that's my opinion as a viewer developer ;-)
>
> Yeah, we're aware of that, and would really like to have something.
> Unfortunately none of the core developers are likely to get to it
> patches and fresh contributers welcome. :)

As everywhere :D 
Now seriously, i'm already overloaded with the things i mantain, and my PS 
knowledge is very near to 0 so i am going to say "No, thanks" to your 
recruitment effort :-)

>
> > For number of pages, we are using a parser that gets the "%%Pages:"
> > stuff. That is easy :-)
>
> You're aware, I guess, that the DSC comments can be wrong or absent.
> There should be some fallback for such cases, either pre-parsing the
> document or just streaming it as it comes. Also, in some documents,
> random access to pages is very expensive.
>
> > The actual problem is knowing the page size. The problem exists because
> > we need to know the page size before the actual rendering of the page to
> > allocate the space in the page area, if not we could just use also the
> > values that come with the display_size callback.
>
> This may also be available from the DSC comment %%BoundingBox, but it
> can be wrong, and of course it's possible to vary from page to page.
>
> The display device is designed the way it is, with all the
> callbacks, so support just streaming the document. For pre-parsing,
> you can run the document through the bbox output device to get
> the page count and the size of each page.

Does the bbox output device do actual rendering? That is, is it fast enough? I 
don't want to render all the ps file (it could take "ages") just to know how 
much pages it has and their sizes.

Also, how do i use the bbox output device from my own code? I did not see any 
easy way to do it.

And now that i'm asking, could you point to me some PS files with different 
page size in each page? 

> So if you want to develop something like this, I'd suggest going with
> something like what you sketched, but make sure it can fall back
> gracefully when the DSC information isn't available or is incorrect.
>
> Also, while get_image() is a reasonable high level call, a viewer
> api should also provide a tile-based call to get a subregion of
> a page at a particular resolution. Otherwise you fall over when
> zoomed in on a large document.

You are right, of course, but we are leaving this problem for future okular 
versions, for now we are concentrating of getting "easy" things to work.

Thanks a lot.

Albert

>
> Anyway, we are happy to offer advice etc. if you want to help develop
> soemthing like this.
>
>  -r