Vertex clipping and primitive types

Bill Spitzak spitzak at
Thu Sep 19 14:09:36 PDT 2013

Sam Spilsbury wrote:
> The point is to any arbitrary geometry against a rectangle. This is 
> used to ensure that redraw areas only stick to damage areas.
I suspect the most efficient thing to do is to clip against the bounding 
box of the obscuring object, even if that produces excess redraw, due to 
the complexity of arbitrary clip exceeding the time saved from the 
smaller redraw. It may be useful to do an accurate test for 
no-intersection, and if they intersect produce a 4-sided intersection of 
both bounding boxes. Also watch out for antialiased edges, the 
mathematically correct intersection test may give a false negative.

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