[Mesa-dev] Mesa (master): r300g: fix gl_PointCoord

Ian Romanick idr at freedesktop.org
Wed Aug 25 00:05:35 PDT 2010

Hash: SHA1

keith whitwell wrote:
> The point state is complex, there are actually a lot of variations
> built into GL itself which aren't obvious on first reading of the
> spec.  Probably the most obscure is that wide points and point sprites
> are specified to actually be rasterized differently, ie color
> different pixels.  I'm doing this from memory, but Roland dug into it
> in depth.  Wide points have an explicit set of rules for which pixels
> they cover, but point sprites are to be rasterized with the same rules
> as a quad of similar size (again from memory).  The docs do explain
> it, but it's complex none the less, and I do still wonder if there is
> a clear way of capturing all the variations.

I remember a lot of back and forth when we crafted the rasterization
rules for point sprites.  I believe the intention was that
implementations could either decompose a point sprite into a quad / two
triangles or reuse the existing wide point rasterization hardware.  At
the end of the day, it is a big mess and a pain in the behind.
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