[cairo] Clip region problems

[Owen Taylor]

On Wed, 2005-05-18 at 11:54 -0700, Keith Packard wrote:

> > * Using a surface as a source for drawing to itself is going to be a
> > problem, but it's already a problem, so that's nothing new.
> 
> Yes, clipping in this environment is ill-defined.  X actually defines
> the clip in this case only for output; input is not affected by
> clipping.

I think this is clearly the semantic we want. The problem is that 
libpixman and RENDER don't work that way. 

For A => B we temporarily clear the clip on A when using it as a source.

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.)

Regards,
					Owen

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