On May 10, Keith Packard wrote:
 > So, the question is whether we should insist that the application provide 
 > a destination alpha channel and use the Disjoint operators for tesselated 
 > figures, or whether we should provide functionality similar to the text 
 > primitives in this case.

>From an interface point of view, I think we definitely want the
pre-adding as is done in the case of the text primitives.

The interface should allow the user to easily composite polygons using
all available operators. If the user specifies the Disjoint/Conjoint
semantics, then that should be an indication of the compositing
behavior desired around the polygon boundary. The user should not have
to indicate the correct operator for compositing the smaller
trapezoids that make up the polygon, (especially since a Disjoint
operator is always desired here, no?).

 > I believe I could implement this common case without requiring a 
 > full-sized temporary alpha map, instead only selected scanlines would 
 > require special treatment, so performance wouldn't suffer too badly.

So, if you can implement it efficiently, I don't see any compelling
reason not to take this approach.

-Carl
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