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authorAnuj Phogat <[email protected]>2016-08-09 15:41:24 -0700
committerAnuj Phogat <[email protected]>2016-08-12 10:45:02 -0700
commitfb1bc5007deebfb1441a24ecacdfa11927ac9b12 (patch)
tree44fd86caf048cd7b90bbaf92697622ffe30997bc /src/mesa/swrast/s_renderbuffer.h
parent1fe36d849cd0b57da681736d5177275b82b1caba (diff)
i965: Change 8x multisample positions
There are no standard sample positions defined in OpenGL and OpenGL ES specs. Implementations have the freedom to pick the positions which give plausible results. But the Vulkan 1.0 spec does define standard sample positions for different sample counts. Defined positions in Vulkan for all the sample counts except 8X match with the positions we set in i965. We have an upcoming plan to share the blorp code between OpenGL and Vulkan driver in near future. Keeping the 8X sample positions same on both the drivers will help us move in that direction. Here is an argument by Neil Roberts (from commit 20250e85) against any advantage of current 8X sample positions over the new ones: "The comment above for the 8x sample positions says that the hardware implements centroid interpolation by picking the centre-most sample that is inside the primitive. That implies that it might be worthwhile to pick a pattern that includes 0.5,0.5. However by experimentation this doesn't seem to actually be the case. With the sample positions in this patch, if I modify the piglit test below so that it instead reports the centroid position, it reports 0.492188,0.421875 which doesn't match any of the positions. If I modify the sample positions so that they include one at exactly 0.5,0.5 it doesn't help and it reports another position which is even further from the center for some reason. arb_gpu_shader5-interpolateAtSample-different Kenneth Graunke experimented with some other patterns that have a higher standard deviation but I think after some discussion it was decided that it would be better to pick the same pattern as the other graphics API in case there are games that rely on this pattern." Observed no regressions in jenkins testing. Signed-off-by: Anuj Phogat <[email protected]> Reviewed-by: Jason Ekstrand <[email protected]>
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