Disable TAA sharpening on alpha (#4227)

* Disable sharpening on alpha

* Changelog

* Move the define below options

* Update TemporalAntialiasing.hlsl

* Update ref images

* update win vulkan image

Co-authored-by: sebastienlagarde <[email protected]>

Author: FrancescoC-unity

TestProjects/HDRP_Tests/Assets/ReferenceImages/Linear/LinuxEditor/Vulkan/None/4053_TAA-FP16Alpha.png

@@ -202,6 +202,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Changed ray tracing acceleration structure build, so that only meshes with HDRP materials are included (case 1322365).
 - Increased path tracing max samples from 4K to 16K (case 1327729).
 - Film grain does not affect the alpha channel.
+- Disable TAA sharpening on alpha channel.
 
 ## [10.3.0] - 2020-12-01
 

TestProjects/HDRP_Tests/Assets/ReferenceImages/Linear/WindowsEditor/Direct3D11/None/4053_TAA-FP16Alpha.png

@@ -11,7 +11,6 @@
     #define CTYPE_SWIZZLE xyz
 #endif
 
-
 #if UNITY_REVERSED_Z
     #define COMPARE_DEPTH(a, b) step(b, a)
 #else
@@ -49,6 +48,8 @@ float4 Fetch4Array(Texture2DArray tex, uint slot, float2 coords, float2 offset,
 // Options
 // ---------------------------------------------------
 
+#define SHARPEN_ALPHA 0 // switch to 1 if you want to enable TAA sharpenning on alpha channel
+
 // History sampling options
 #define BILINEAR 0
 #define BICUBIC_5TAP 1
@@ -717,5 +718,11 @@ CTYPE SharpenColor(NeighbourhoodSamples samples, CTYPE color, float sharpenStren
     linearC = linearC + (linearC - linearAvg) * sharpenStrength * 3;
     linearC = clamp(linearC, 0, CLAMP_MAX);
 #endif
-    return linearC * PerceptualWeight(linearC);
+    CTYPE outputSharpened = linearC * PerceptualWeight(linearC);
+
+#if (SHARPEN_ALPHA == 0 && defined(ENABLE_ALPHA))
+    outputSharpened.a = color.a;
+#endif
+
+    return outputSharpened;
 }