[cairo] Clipping performance

[Jonathan Roewen]

Hi,

I'm using cairo-0.4.0, and I just have to say your clipping code is
SLOW. I clip to one rectangle, then a 2nd, creating a smaller
intersected rectangle, and to redraw just that clipped area is slower
than drawing the whole image with no clipping set.

I think this is a huge problem .. maybe you've fixed in 0.5.0, but
just want to point our this serious bottleneck, at least in my
application.

Jonathan