tree 8c02130cd1fc037fc23593189decc3c4a1b9e102
parent 52bd6b7da6a758888e99436656e836f178b762af
author Jiawei Shao <jiawei.shao@intel.com> 1569828477 +0000
committer Commit Bot service account <commit-bot@chromium.org> 1569828477 +0000

Set writemask to 0 when no fs output matches color state on Metal and Vulkan

This patch fixes an undefined behaviour on Metal and Vulkan when there
is a color state whose corresponding fragment output is not declared in
the fragment shader.

According to Vulkan SPEC (Chapter 14.3), the input values to blending or
color attachment writes are undefined for components which do not
correspond to a fragment shader output. Vulkan validation layer follows
the SPEC that it only allows the shader to not produce a matching output
if the writemask is 0, or it will report a warning when the application
is against this rule.

When no fragment output matches the color state in a render pipeline,
the output differs on different Metal devices. On some Metal devices the
fragment output will be (0, 0, 0, 0) even if it is not declared in the
shader, while on others there will be no fragment outputs and the content
in the color attachments is not changed.

This patch fixes this issue by setting the color write mask to 0 to
prevent the undefined values being written into the color attachments.

With this patch, the following end2end tests will not report warnings
any more when we enable the Vulkan validation layer:
ObjectCachingTest.RenderPipelineDeduplicationOnLayout/Vulkan
ObjectCachingTest.RenderPipelineDeduplicationOnVertexModule/Vulkan
ObjectCachingTest.RenderPipelineDeduplicationOnFragmentModule/Vulkan

BUG=dawn:209
TEST=dawn_end2end_tests

Change-Id: I5613daa1b9a45349ea1459fbdfe4a12d6149f0f7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/11581
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>