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spirv: Lower BaseVertex to FIRST_VERTEX instead of BASE_VERTEX

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The base vertex in Vulkan is different from GL in that for non-indexed
primitives the value is taken from the firstVertex parameter instead
of being set to zero. This coincides with the new SYSTEM_VALUE_FIRST_VERTEX
instead of BASE_VERTEX.

v2 (idr): Add comment describing why SYSTEM_VALUE_FIRST_VERTEX is used
for SpvBuiltInBaseVertex.  Suggested by Jason.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> [v1]
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This commit is contained in:
Neil Roberts
2018-01-25 19:15:41 +01:00
committed by Ian Romanick
parent c32e1035cb
commit c4f30a9100
3 changed files with 18 additions and 5 deletions
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5
src/compiler/spirv/vtn_variables.c
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@@ -1296,7 +1296,10 @@ vtn_get_builtin_location(struct vtn_builder *b,
set_mode_system_value(b, mode);
break;
case SpvBuiltInBaseVertex:
*location = SYSTEM_VALUE_BASE_VERTEX;
/* OpenGL gl_BaseVertex (SYSTEM_VALUE_BASE_VERTEX) is not the same
* semantic as SPIR-V BaseVertex (SYSTEM_VALUE_FIRST_VERTEX).
*/
*location = SYSTEM_VALUE_FIRST_VERTEX;
set_mode_system_value(b, mode);
break;
case SpvBuiltInBaseInstance: