Hello guys,

My name is Chen, and I’m working on linux-opengl compatibility tests for
embedded design. I am using MESA as reference code.

As far as i understand opengl require to sample at pixel centers (e.g.
(0.5,0.5) (1.5, 0,5) and so on...) and check if that exact point lies inside
a triangle.

Mesa swrast has had TRIANGLE_WALK_DOUBLE in config.h which allowed working
with double precision numbers instead of fixed point and snapping
coordinates . when i turn it on and off i get different results of the final
picture. my questions are 
1. Do both modes (e.g. double and fixed) test if a sampled pixel center is
inside the triangle, from the calculation i'm not sure. 
2. what is Mesa swrast tie breaker rule when a sampled point lies on a
shared edge that is shared by two triangles?
3. my guess is that fixed point snaps somewhere around the pixel center and
not the exact center.

I know that Mesa doesnt exactly samples, it does some complicated setup and
than scanline using that setup but if someone can describe in words how this
correspands to sampling i would be most grateful.
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