[cairo] [PATCH] rectangle clipping regions
cworth at east.isi.edu
Thu Mar 18 06:21:37 PST 2004
On Dec 15, graydon hoare wrote:
> - new call: cairo_init_clip (cairo_t *cr); which resets the clip
> region to the entire device. mimics what postscript does here,
This looks just fine. Adding new API calls that match PostScript
> - new surface backend function:
> (*set_clip_region) (void *surface,
> pixman_region16_t *region);
This looks fine too. As far as the internal backend interface, pretty
much anything that gets the job done is OK with me, (though I do want
to do some housekeeping in that department soon).
> - new functionality in cairo_gstate: gstate holds both a clip
> mask and a clip region (possibly NULL). when cairo_clip runs,
This seems like a slick feature. It should satisfy the need for fast
clipping of pixel-aligned rectangles, but without complicating the
API. Well done.
> there are a couple FIXMEs: I don't know what to do on the postscript
OK. I may be able to look at the PS backend sometime, (it's actually
simpler than it looks, basically it all just defers to the image
backend for everything --- though the code path there isn't obvious at
I would not like to see this committed unless we're sure that the PS
backend is still working.
> and I don't have a particularly good epsilon available for
> measuring pixel alignment of the clip path (I'm currently checking to
> see if bits 8-15 are clear).
At this point, you've got a fixed-point value so no epsilon should be
necessary. You just want to check if the sub-pixel portion is 0. So
just modify the code to check that bits 0-15 are clear. (Note: I had
misread the code when I made an earlier offline comment to you.)
> I'm also not sure if:
> - the clip should always be added to the mask *as well* as the region
> - the bounding box of non-rectangular paths should be added to the
> region, perhaps to speed up compositing (?)
To me, those both sound like further optimizations. They're probably a
good idea, but since all of this work is just optimization anyway,
there's no need to delay this patch for these.
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