[URP][2023.2] Backport UUM-47142 Screen Space Decal Ambient Lighting

- Fixes the following issue: [UUM-47142](https://jira.unity3d.com/browse/UUM-47142) Frag() in ShaderPassDecal.hlsl when using deferred rendering pipeline can potentially use an uninitialized world space normal when calculating inputData.bakedGI. So, as is done just above for screen space the normal is initialized ahead of time so GI can be calculated correctly and passed on to the final output data.

Author: skip-petty

Packages/com.unity.render-pipelines.universal/Editor/ShaderGraph/Includes/ShaderPassDecal.hlsl

@@ -328,6 +328,12 @@ void Frag(PackedVaryings packedInput,
     outColor = color;
 #elif defined(DECAL_GBUFFER)
 
+    // Need to reconstruct normal here for inputData.bakedGI, but also save off surfaceData.normalWS for correct GBuffer blending
+    half3 normalToPack = surfaceData.normalWS.xyz;
+#ifdef DECAL_RECONSTRUCT_NORMAL
+    surfaceData.normalWS.xyz = normalize(lerp(normalWS.xyz, surfaceData.normalWS.xyz, surfaceData.normalWS.w));
+#endif
+
     InputData inputData;
     InitializeInputData(input, positionWS, surfaceData.normalWS.xyz, viewDirectionWS, inputData);
 
@@ -339,21 +345,15 @@ void Frag(PackedVaryings packedInput,
 
     // Skip GI if there is no abledo
 #ifdef _MATERIAL_AFFECTS_ALBEDO
-
-    // GI needs blended normal
-#ifdef DECAL_RECONSTRUCT_NORMAL
-    half3 normalGI = normalize(lerp(normalWS.xyz, surfaceData.normalWS.xyz, surfaceData.normalWS.w));
-#endif
-
     Light mainLight = GetMainLight(inputData.shadowCoord, inputData.positionWS, inputData.shadowMask);
-    MixRealtimeAndBakedGI(mainLight, normalGI, inputData.bakedGI, inputData.shadowMask);
-    half3 color = GlobalIllumination(brdfData, inputData.bakedGI, surface.occlusion, normalGI, inputData.viewDirectionWS);
+    MixRealtimeAndBakedGI(mainLight, surfaceData.normalWS.xyz, inputData.bakedGI, inputData.shadowMask);
+    half3 color = GlobalIllumination(brdfData, inputData.bakedGI, surface.occlusion, surfaceData.normalWS.xyz, inputData.viewDirectionWS);
 #else
     half3 color = 0;
 #endif
 
     // We can not use usual GBuffer functions (etc. BRDFDataToGbuffer) as we use alpha for blending
-    half3 packedNormalWS = PackNormal(surfaceData.normalWS.xyz);
+    half3 packedNormalWS = PackNormal(normalToPack);
     fragmentOutput.GBuffer0 = half4(surfaceData.baseColor.rgb, surfaceData.baseColor.a);
     fragmentOutput.GBuffer1 = 0;
     fragmentOutput.GBuffer2 = half4(packedNormalWS, surfaceData.normalWS.a);