[Mesa-dev] [PATCH 02/10] spirv: Make VertexIndex and VertexId both non-zero-based
apinheiro at igalia.com
Thu Aug 9 13:43:44 UTC 2018
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
@@ -1011,15 +1011,16 @@ vtn_get_builtin_location(struct vtn_builder *b,
*location = VARYING_SLOT_CULL_DIST0;
- case SpvBuiltInVertexIndex:
- *location = SYSTEM_VALUE_VERTEX_ID;
- set_mode_system_value(b, mode);
- /* 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;
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