On Thu, Sep 17, 2015 at 05:00:04PM +0100, Neil Roberts wrote: > This is the standard pattern used by the other 3D graphics API. > > BDW has slots for these values, but they aren't actually used until > SKL. Even though the documentation for BDW says they must be zero, it > doesn't seem to cause any harm to program them anyway. > > 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. > > (Based on a patch by Kenneth Graunke) > > Cc: Kenneth Graunke <kenn...@whitecape.org>
Reviewed-by: Ben Widawsky <b...@bwidawsk.net> _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
