Mesa (master): spirv: Make VertexIndex and VertexId both non-zero-based
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Mon Aug 13 14:30:36 UTC 2018
Module: Mesa
Branch: master
Commit: be6f472b2387f508e55ffbe758da8cbea75717d6
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=be6f472b2387f508e55ffbe758da8cbea75717d6
Author: Neil Roberts <nroberts at igalia.com>
Date: Thu Apr 19 17:17:41 2018 +0200
spirv: Make VertexIndex and VertexId both non-zero-based
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. In Vulkan VertexId
and InstanceId have no meaning and are pretty much just reserved for
OpenGL at this point.
GL_ARB_spirv removes VertexIndex and defines VertexId to be the same
as gl_VertexId (which is also 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 value.
v2: update comment and commit descriptions, based on Jason Ekstrand
explanation of the meaning/rationale behind all those builtins
(Jason)
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
---
src/compiler/spirv/vtn_variables.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/src/compiler/spirv/vtn_variables.c b/src/compiler/spirv/vtn_variables.c
index 8dab86abd7..571a14cf4c 100644
--- a/src/compiler/spirv/vtn_variables.c
+++ b/src/compiler/spirv/vtn_variables.c
@@ -1011,15 +1011,15 @@ vtn_get_builtin_location(struct vtn_builder *b,
case SpvBuiltInCullDistance:
*location = VARYING_SLOT_CULL_DIST0;
break;
- 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:
+ /* The Vulkan spec defines VertexIndex to be non-zero-based and doesn't
+ * allow VertexId. The ARB_gl_spirv spec defines VertexId to be the
+ * same as gl_VertexID, which is non-zero-based, and removes
+ * VertexIndex. Since they're both defined to be non-zero-based, we use
+ * SYSTEM_VALUE_VERTEX_ID for both.
*/
- *location = SYSTEM_VALUE_VERTEX_ID_ZERO_BASE;
+ *location = SYSTEM_VALUE_VERTEX_ID;
set_mode_system_value(b, mode);
break;
case SpvBuiltInInstanceIndex:
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