Question about XRender specification

[Clemens Eisserer]

Hello,

I have some problems understanding the following behaviour:

> Abutting edges must match precisely.  When specifying two polygons
> abutting along a common edge, if that edge is specified with the
> same coordinates in each polygon then the sum of alpha values for
> pixels inside the union of the two polygons must be precisely one.

When I have two trapezoids, where the first ends at 100/90  and the
second begins at 100/90 (speaking about the horizontal edges) -
shouldn't both accumulate to one large and seamless trap. If not,
whats wrong with my testcase?

Thank you in advance, lg Clemens