Consider dynamically indexed gl_Position in mesh.

whhuawei · Jul 3, 2023 · 8ec95fb · 8ec95fb
1 parent 601b60c
commit 8ec95fb
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Showing 3 changed files with 26 additions and 11 deletions.
diff --git a/...ders-hlsl-no-opt/mesh/mesh-shader-basic-triangle.spv14.vk.nocompat.nofxc.flip-vert-y.mesh b/...ders-hlsl-no-opt/mesh/mesh-shader-basic-triangle.spv14.vk.nocompat.nofxc.flip-vert-y.mesh
@@ -1,3 +1,7 @@
+#ifndef SPIRV_CROSS_CONSTANT_ID_0
+#define SPIRV_CROSS_CONSTANT_ID_0 1
+#endif
+static const int spec_const_index = SPIRV_CROSS_CONSTANT_ID_0;
 static const uint3 gl_WorkGroupSize = uint3(2u, 3u, 4u);
 
 struct BlockOut
@@ -57,6 +61,8 @@ void mesh_main(inout gl_MeshPerVertexEXT gl_MeshVerticesEXT[24], inout uint3 gl_
     gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.x = _46.x;
     gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.z = _46.y;
     gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.w = _46.z;
+    gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position[gl_LocalInvocationIndex % 4u] = float(gl_GlobalInvocationID.z);
+    gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position[spec_const_index] = spvFlipVertY(float(gl_GlobalInvocationID.z));
     gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_ClipDistance[0] = 4.0f;
     gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_CullDistance[0] = 3.0f;
     gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_CullDistance[1] = 5.0f;

diff --git a/shaders-hlsl-no-opt/mesh/mesh-shader-basic-triangle.spv14.vk.nocompat.nofxc.flip-vert-y.mesh b/shaders-hlsl-no-opt/mesh/mesh-shader-basic-triangle.spv14.vk.nocompat.nofxc.flip-vert-y.mesh
@@ -28,23 +28,27 @@ struct TaskPayload
 	int c;
 };
 
+layout(constant_id = 0) const int spec_const_index = 1;
+
 taskPayloadSharedEXT TaskPayload payload;
 
 void main()
 {
 	SetMeshOutputsEXT(24, 22);
 
-  gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position = vec4(gl_GlobalInvocationID, 1.0);
-  gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.y = float(gl_WorkGroupID);
-  gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.xzw = vec3(gl_GlobalInvocationID);
+	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position = vec4(gl_GlobalInvocationID, 1.0);
+	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.y = float(gl_WorkGroupID);
+	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position.xzw = vec3(gl_GlobalInvocationID);
+	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position[gl_LocalInvocationIndex % 4] = float(gl_GlobalInvocationID.z);
+	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_Position[spec_const_index] = float(gl_GlobalInvocationID.z);
 
 	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_ClipDistance[0] = 4.0;
 	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_CullDistance[0] = 3.0;
-  gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_CullDistance[1] = 5.0;
+	gl_MeshVerticesEXT[gl_LocalInvocationIndex].gl_CullDistance[1] = 5.0;
 
 	barrier();
 	if (gl_LocalInvocationIndex < 22)
-  {
-    gl_PrimitiveTriangleIndicesEXT[gl_LocalInvocationIndex] = uvec3(0, 1, 2) + gl_LocalInvocationIndex;
+	{
+		gl_PrimitiveTriangleIndicesEXT[gl_LocalInvocationIndex] = uvec3(0, 1, 2) + gl_LocalInvocationIndex;
 	}
 }
diff --git a/spirv_glsl.cpp b/spirv_glsl.cpp
@@ -10313,17 +10313,22 @@ string CompilerGLSL::access_chain_internal(uint32_t base, const uint32_t *indice
 
 			if (access_meshlet_position_y)
 			{
-				uint32_t id = 0;
 				if (is_literal)
 				{
-					id = index;
+					access_meshlet_position_y = index == 1;
 				}
 				else
 				{
-					auto &c = get<SPIRConstant>(index);
-					id = c.scalar();
+					const auto *c = maybe_get<SPIRConstant>(index);
+					if (c)
+						access_meshlet_position_y = c->scalar() == 1;
+					else
+					{
+						// We don't know, but we have to assume no.
+						// Flip Y in mesh shaders is an opt-in horrible hack, so we'll have to assume shaders try to behave.
+						access_meshlet_position_y = false;
+					}
 				}
-				access_meshlet_position_y = (id == 1);
 			}
 
 			expr += deferred_index;