[Mesa-dev] [PATCH 02/10] spirv: Make VertexIndex and VertexId both non-zero-based
apinheiro at igalia.com
Mon Aug 13 13:08:43 UTC 2018
This is the only pending patch from this series, would appreciate a
review. As everything involving the VertexIndex/Id, it is somewhat
tricky. I'm CCing Kenneth too as he was involved on the OpenGL mess with
gl_VertexId and similar.
FWIW, I already executed the Intel CI, and there are no regressions.
On 09/08/18 15:43, Alejandro Piñeiro wrote:
> From: Neil Roberts <nroberts at igalia.com>
> GLSL has gl_VertexID which is supposed to be non-zero-based.
> SPIR-V has both VertexIndex and VertexId builtins whose meanings are
> defined by the APIs.
> Vulkan defines VertexIndex as being non-zero-based. I can’t find
> any mention of what VertexId is supposed to be.
> GL_ARB_spirv removes VertexIndex and defines VertexId to be the same
> as gl_VertexId (which is alo non-zero-based).
> Previously in Mesa it was treating VertexIndex as non-zero-based and
> VertexId as zero-based, so it was breaking for GL. This behaviour was
> apparently based on Khronos bug 14255. However that bug doesn’t seem
> to have made a final decision for VertexId.
> Assuming there really is no other definition for VertexId for Vulkan
> it seems better to just make them both have the same
> src/compiler/spirv/vtn_variables.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
> diff --git a/src/compiler/spirv/vtn_variables.c b/src/compiler/spirv/vtn_variables.c
> index 8dab86abd74..b92bda59828 100644
> --- a/src/compiler/spirv/vtn_variables.c
> +++ b/src/compiler/spirv/vtn_variables.c
> @@ -1011,15 +1011,16 @@ vtn_get_builtin_location(struct vtn_builder *b,
> case SpvBuiltInCullDistance:
> *location = VARYING_SLOT_CULL_DIST0;
> - case SpvBuiltInVertexIndex:
> - *location = SYSTEM_VALUE_VERTEX_ID;
> - set_mode_system_value(b, mode);
> - break;
> case SpvBuiltInVertexId:
> - /* Vulkan defines VertexID to be zero-based and reserves the new
> - * builtin keyword VertexIndex to indicate the non-zero-based value.
> + case SpvBuiltInVertexIndex:
> + /* For whatever reason, both of these are defined in the SPIR-V spec.
> + * The Vulkan spec defines VertexIndex to be non-zero-based and doesn’t
> + * mention VertexId. The ARB_gl_spirv spec defines VertexId to be the
> + * same as gl_VertexID, which is non-zero-based, and removes
> + * VertexIndex. Assuming there is no use for VertexId in Vulkan yet, we
> + * can just make them both be the same.
> - *location = SYSTEM_VALUE_VERTEX_ID_ZERO_BASE;
> + *location = SYSTEM_VALUE_VERTEX_ID;
> set_mode_system_value(b, mode);
> case SpvBuiltInInstanceIndex:
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