[cairo] strange trapezoid produced by cairo

[M Joonas Pihlaja]

Hi Kamaal,

On Wed, 28 May 2008, kammal wrote:

[snip unantialiased-shapes test produces a self-intersecting
trapezoid]

> Is this a valid trapezoid?

No. :(

> Is this a bug in cairo, or I am not taking care of something?

It's a bug in cairo's tessellator which appears to affect some
rightmost trapezoids which self-intersect -- they're not emitted
soon enough at the intersection point.  The bug seems to be
masked when rasterising because pixman doesn't render backward
spans and stops when it detects the intersection.

Cheers,

Joonas