Clarify the PointCoord calculation
Bug: b/149537975
Change-Id: Ia589e0015437e5257991fe2e8b5f6459384a76de
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/42048
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
diff --git a/src/Pipeline/PixelProgram.cpp b/src/Pipeline/PixelProgram.cpp
index b92d48e..da26158 100644
--- a/src/Pipeline/PixelProgram.cpp
+++ b/src/Pipeline/PixelProgram.cpp
@@ -88,10 +88,11 @@
routine.setInputBuiltin(spirvShader, spv::BuiltInPointCoord, [&](const SpirvShader::BuiltinMapping &builtin, Array<SIMD::Float> &value) {
assert(builtin.SizeInComponents == 2);
- Float pointSizeFactor = *Pointer<Float>(primitive + OFFSET(Primitive, pointSizeInv));
- value[builtin.FirstComponent + 0] = SIMD::Float(0.5f) + SIMD::Float(pointSizeFactor) * (((SIMD::Float(Float(x)) + SIMD::Float(0.f, 1.f, 0.f, 1.f)) - SIMD::Float(*Pointer<Float>(primitive + OFFSET(Primitive, pointCoordX)))));
-
- value[builtin.FirstComponent + 1] = SIMD::Float(0.5f) + SIMD::Float(pointSizeFactor) * (((SIMD::Float(Float(y)) + SIMD::Float(0.f, 0.f, 1.f, 1.f)) - SIMD::Float(*Pointer<Float>(primitive + OFFSET(Primitive, pointCoordY)))));
+ // PointCoord formula reference: https://www.khronos.org/registry/vulkan/specs/1.2/html/vkspec.html#primsrast-points-basic
+ // Note we don't add a 0.5 offset to x and y here (like for fragCoord) because pointCoordX/Y have 0.5 subtracted as part of the viewport transform.
+ SIMD::Float pointSizeInv = SIMD::Float(*Pointer<Float>(primitive + OFFSET(Primitive, pointSizeInv)));
+ value[builtin.FirstComponent + 0] = SIMD::Float(0.5f) + pointSizeInv * (((SIMD::Float(Float(x)) + SIMD::Float(0.0f, 1.0f, 0.0f, 1.0f)) - SIMD::Float(*Pointer<Float>(primitive + OFFSET(Primitive, pointCoordX)))));
+ value[builtin.FirstComponent + 1] = SIMD::Float(0.5f) + pointSizeInv * (((SIMD::Float(Float(y)) + SIMD::Float(0.0f, 0.0f, 1.0f, 1.0f)) - SIMD::Float(*Pointer<Float>(primitive + OFFSET(Primitive, pointCoordY)))));
});
routine.setInputBuiltin(spirvShader, spv::BuiltInSubgroupSize, [&](const SpirvShader::BuiltinMapping &builtin, Array<SIMD::Float> &value) {
