swr: [rasterizer jitter] Fix logic bug for alpha-to-coverage.

1 files changed, 11 insertions, 2 deletions

diff --git a/src/gallium/drivers/swr/rasterizer/jitter/blend_jit.cpp b/src/gallium/drivers/swr/rasterizer/jitter/blend_jit.cpp
index 2fed2bf4831..a64f86006f4 100644
--- a/src/gallium/drivers/swr/rasterizer/jitter/blend_jit.cpp
+++ b/src/gallium/drivers/swr/rasterizer/jitter/blend_jit.cpp
@@ -576,9 +576,12 @@ struct BlendJit : public Builder
             src1[i] = LOAD(pSrc1, { i });
         }
         Value* currentMask = VIMMED1(-1);
-        if(state.desc.alphaToCoverageEnable)
+        if (state.desc.alphaToCoverageEnable)
         {
-            currentMask = FP_TO_SI(FMUL(src[3], VBROADCAST(C((float)state.desc.numSamples))), mSimdInt32Ty);
+            Value* pClampedSrc = FCLAMP(src[3], 0.0f, 1.0f);
+            uint32_t bits = (1 << state.desc.numSamples) - 1;
+            currentMask = FMUL(pClampedSrc, VBROADCAST(C((float)bits)));
+            currentMask = FP_TO_SI(FADD(currentMask, VIMMED1(0.5f)), mSimdInt32Ty);
         }
 
         // alpha test
@@ -702,6 +705,12 @@ struct BlendJit : public Builder
             currentMask = AND(sampleMask, currentMask);
         }
 
+        if (state.desc.alphaToCoverageEnable)
+        {
+            Value* sampleMasked = SHL(C(1), sampleNum);
+            currentMask = AND(currentMask, VBROADCAST(sampleMasked));
+        }
+
         if(state.desc.sampleMaskEnable || state.desc.alphaToCoverageEnable ||
            state.desc.oMaskEnable)
         {