On Mon, Nov 16, 2015 at 6:03 PM, Ilia Mirkin <imir...@alum.mit.edu> wrote: > On Mon, Nov 16, 2015 at 8:31 AM, Nicolai Hähnle <nhaeh...@gmail.com> wrote: >> Hi Glenn, >> >> On 14.11.2015 00:11, Glenn Kennard wrote: >>> >>> On Fri, 13 Nov 2015 18:57:28 +0100, Nicolai Hähnle <nhaeh...@gmail.com> >>> wrote: >>> >>>> On 13.11.2015 00:14, Glenn Kennard wrote: >>>>> >>>>> Signed-off-by: Glenn Kennard <glenn.kenn...@gmail.com> >>>>> --- >>>>> Maybe there is a better way to check if a thread is a helper invocation? >>>> >>>> >>>> Is ctx->face_gpr guaranteed to be initialized when >>>> load_helper_invocation is called? >>>> >>> >>> allocate_system_value_inputs() sets that if needed, and is called before >>> parsing any opcodes. >> >> >> Sorry, you're right, I missed the second change to the inputs array there. >> >> >>>> Aside, I'm not sure I understand correctly what this is supposed to >>>> do. The values you're querying are related to multi-sampling, but my >>>> understanding has always been that helper invocations can also happen >>>> without multi-sampling: you always want to process 2x2 quads of pixels >>>> at a time to be able to compute derivatives for texture sampling. When >>>> the boundary of primitive intersects such a quad, you get helper >>>> invocations outside the primitive. >>>> >>> >>> Non-MSAA buffers act just like 1 sample buffers with regards to the >>> coverage mask supplied by the hardware, so helper invocations which have >>> no coverage get a 0 for the mask value, and normal fragments get 1. >>> Works with the piglit test case posted at least... >> >> >> Here's why I'm still skeptical: According to the GLSL spec, the fragment >> shader is only run once per pixel by default, even when MSAA is enabled. >> _However_, if a shader statically accesses the SampleID, _then_ it must be >> run once per fragment. The way I understand it, your change forces the >> fragment shader to access SampleID, even when people ostensibly use >> HelperInvocation in the hope of optimizing something. > > GPU's don't operate based on GLSL specs. Per-sample shading is enabled > separately.
FYI, per-sample shading is controlled by pipe_context::set_min_samples. Other states can't turn it on. Marek _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
