[cairo-bugs] [Bug 11379] Callback based pixel backend

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Wed Jun 27 11:27:37 PDT 2007


------- Comment #3 from cworth at cworth.org  2007-06-27 11:27 PST -------
(In reply to comment #2)
> Hmm. I guess we are about to mix two issues here:
>   a) I'd like to be able to draw parts ("tiles") of an image without having to
>       - store the complete image in a huge buffer
>       - draw the drawing again and again for the next tiles.
>   b) Make it possible for applications to provide custom callback-functions
> that
>      receive calculated color values and are free to put these into memory in
>      whatever format they need later.

Yes, those are definitely two different issues. So, is anything
missing from cairo for (a)? And for (b) can you provide me anything
like a detail of what a callback would look like in terms of cairo's
imaging model? I understand that libart provides to a callback a set
of run-length encoded alpha values. And that is sufficient for
capturing the result of rasterization, but cairo's imaging model
includes a lot more than rasterization. When you say "cairo_stroke"
you're asking for the path to be rasterized, yes, but also for source
pattern to be intersected with that mask and the result to be blended
with the destination. How would that all fit into a proposed callback

Meanwhile, I think the issue of "how should cairo be enhanced so that
gimp can make good use of it" is extremely interesting. And I also
think that bugzilla is an awful place for that discussion, (we have a
_lot_ more people reading the cairo mailing list than random bugs in

Could you please open this discussion on the cairo mailing list?



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