[cairo] Clip region problems
keithp at keithp.com
Wed May 18 13:29:30 PDT 2005
On Wed, 2005-05-18 at 15:49 -0400, Owen Taylor wrote:
> I think this is clearly the semantic we want. The problem is that
> libpixman and RENDER don't work that way.
I think the right answer is 'it depends'. Render, by creating an
intermediate object (Picture) permits either semantic by allowing
multiple Pictures for a single Drawable.
> For A => B we temporarily clear the clip on A when using it as a source.
Or, we can simply define the backend semantics to not clip the source,
the xlib Render backend would then need to create separate picture
objects for source and destination operands.
A more complete solution would include a clip region in the pattern
object. It would, of course, be nice to share these somehow saving
ourselves a picture object and ancilary region.
> But for A => A we need to "fork" the input surface when operating from a
> surface to itself with a clip. (Create another Picture really.)
I guess the question is how the PDF, Quartz and Win32 backends might
deal with separate input/output clip regions. If they already have this
ability, then we're all set. Otherwise, we should consider what
reasonable subset of the complete functionality is efficiently
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