Merge pull request #114 from Unity-Technologies/Update-weights-calculation

HDRenderPipeline: Update weight calculation for layering

Assets/ScriptableRenderLoop/HDRenderPipeline/Lighting/TilePass/TilePass.cs

             public int debugViewTilesFlags = 0;
             public bool enableClustered = false;
             public bool disableFptlWhenClustered = true;    // still useful on opaques. Should be false by default to force tile on opaque.
-            public bool enableBigTilePrepass = false;
+            public bool enableBigTilePrepass = true;
             const bool k_UseDepthBuffer = true;      // only has an impact when EnableClustered is true (requires a depth-prepass)
             const bool k_UseAsyncCompute = true;        // should not use on mobile
 

Assets/ScriptableRenderLoop/HDRenderPipeline/Material/Lit/LitData.hlsl

     masks[3] = inputMasks.b;
 
     // calculate weight of each layers
-    float left = 1.0f;
+    // Algorithm is like this:
+    // Top layer have priority on others layers
+    // If a top layer doesn't use the full weight, the remaining can be use by the following layer.
+    float weightsSum = 0.0;
-    for (int i = _LAYER_COUNT - 1; i > 0; --i)
+    for (int i = _LAYER_COUNT - 1; i >= 0; --i)
-        outWeights[i] = masks[i] * left;
-        left -= outWeights[i];
+        outWeights[i] = min(masks[i], (1.0 - weightsSum));
+        weightsSum = saturate(weightsSum + masks[i]);
-    outWeights[0] = left;
 }
 
 float3 BlendLayeredFloat3(float3 x0, float3 x1, float3 x2, float3 x3, float weight[4])