[cairo] PDF Backend for cairo

[David Reveman]

On Wed, 2004-12-01 at 02:16 -0500, Kristian Høgsberg wrote:
> Carl Worth wrote:
> > On Mon, 29 Nov 2004 14:59:09 -0500, =?ISO-8859-1?Q?Kristian_H=F8gsberg?= wrote:
> > 
> >>I've been working on a PDF backend for cairo over the weekend, and at 
> >>this point I think it's appropriate post a snapshot of the current code. 
> > 
> > Fantastic! It's great to see more progress continuing on this front.
> 
> Well, here's a little more progress:
> 
> 	- I found the problem with the "leak" in the polygons, I misunderstood 
> the trapezoid format.
> 	- As described in my other mail, I changed the generated PDF to draw 
> all trapezoids as subpaths of one big path and the fill that for each 
> call to composite_trapezoids() which solves the problem with cracks in 
> the polygons.
> 	- I added support for constant alpha values
> 	- I added support for clipping paths
> 
> I've uploaded a new patch with these changes:
> 
>    http://people.redhat.com/krh/cairo-pdf/cairo-pdf-2.patch
> 
> and there's an updated snippets.pdf available:
> 
>    http://people.redhat.com/krh/cairo-pdf/snippets.pdf
> 
> The clipping support requires a change to the backend API: I added a 
> set_clip_trapezoids() call to cairo_surface_backend_t which works much 
> like set_clip_region(), except it takes a list of trapezoids for the 
> clipping area.  If a backend doesn't support this it must return 
> CAIRO_INT_STATUS_UNSUPPORTED as usual.  This change isn't fully done 
> yet, there's a few issues to work out still.
> 
> By the way, in _cairo_gstate_clip() line 1761, the rectangle case ends with:
> 
>          if (status != CAIRO_INT_STATUS_UNSUPPORTED) {
>              _cairo_traps_fini (&traps);
>          }
>          return status;
> 
> Shouldn't this be
> 
>          if (status != CAIRO_INT_STATUS_UNSUPPORTED) {
>              _cairo_traps_fini (&traps);
>              return status;
>          }
> 
> instead?

Exactly. Some time ago I sent a mail to Graydon Hoare who changed this
on 2004-11-05 to have it reverted but I haven't heard back from him yet.
It breaks clipping for all backends that can't handle clipping regions,
so getting it fixed is quite important.

> 
> Oh, and another thing: it looks like the show_glyphs function pointer in 
> the cairo_surface_backend_t struct can be NULL, in which case it is 
> treated as returning CAIRO_INT_STATUS_NOT_SUPPORTED.  Is there a reason 
> show_glyphs doesn't follow the convention that all function pointers 
> must be non-NULL?
> 
> cheers,
> Kristian
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-David