[cairo] new trapezoid code in glitz

[Bill Spitzak]

David Reveman wrote:

> "non-intersecting" was the wrong word. By "non-intersecting" I meant; no
> pixel is intersected by more than one trapezoid.
> 
> So in my previous mail:
> "non-intersecting" = no pixel is intersected by more than one trapezoid
> "intersecting" = at least one pixel is intersected by more than one
> trapezoid
> 
> Sorry for any confusion this might have caused.

Actually I am still confused.

I'm pretty certain that "intersecting" includes trapazoids that are 
close enough together that their antialiased pixels overlap, even though 
they in reality do not overlap if drawn at infinite resolution. Is this 
correct?

PS: Ignoring this case and drawing the trapazoids one after the other is 
VERY common, in fact so common that lots of programs rely on the 
incorrect result being produced. For this reason it may be necessary to 
ignore it as well.