Merge pull request #337 from Unity-Technologies/Branch_ImproveAreaLightVGPR

Improved VGPR pressure for Area Light lighting code.

Assets/ScriptableRenderPipeline/HDRenderPipeline/Lighting/LightDefinition.cs

         ProjectorPyramid,
 
         // AreaLight
+        Line, // Keep Line lights before Rectangle. This is needed because of a compiler bug (see LightLoop.hlsl)
-        Line,
         // Currently not supported in real time (just use for reference)
         Sphere,
         Disk,

Assets/ScriptableRenderPipeline/HDRenderPipeline/Lighting/LightDefinition.cs.hlsl

 #define GPULIGHTTYPE_SPOT (2)
 #define GPULIGHTTYPE_POINT (3)
 #define GPULIGHTTYPE_PROJECTOR_PYRAMID (4)
-#define GPULIGHTTYPE_RECTANGLE (5)
-#define GPULIGHTTYPE_LINE (6)
+#define GPULIGHTTYPE_LINE (5)
+#define GPULIGHTTYPE_RECTANGLE (6)
 #define GPULIGHTTYPE_SPHERE (7)
 #define GPULIGHTTYPE_DISK (8)
 #define GPULIGHTTYPE_HEMISPHERE (9)

Assets/ScriptableRenderPipeline/HDRenderPipeline/Lighting/TilePass/TilePassLoop.hlsl

 #ifdef PROCESS_AREA_LIGHT
     if(featureFlags & LIGHTFEATUREFLAGS_AREA)
     {
-        // TODO: Convert the for loop below to a while on each type as we know we are sorted!
-        for(i = 0; i < areaLightCount; ++i)
+
+        float3 localDiffuseLighting = float3(0.0, 0.0, 0.0);
+        float3 localSpecularLighting = float3(0.0, 0.0, 0.0);
+
+        // !!!!!!!!!!!!!!
+        // COMPILER BEHAVIOR WARNING
+        // If rectangle lights are before line lights, the compiler will duplicate light matrices in VGPR because they are used differently between the two types of lights.
+        // By keeping line lights first we avoid this behavior and save substantial register pressure.
+
+        i = 0;
+        uint areaIndex = FetchIndex(areaLightStart, i);
+        while ( i < areaLightCount && _LightDatas[areaIndex].lightType == GPULIGHTTYPE_LINE)
-            float3 localDiffuseLighting, localSpecularLighting;
+            areaIndex = FetchIndex(areaLightStart, i);
+            EvaluateBSDF_Line(  context, V, posInput, prelightData, _LightDatas[areaIndex], bsdfData,
+                                localDiffuseLighting, localSpecularLighting);
-            uint areaIndex = FetchIndex(areaLightStart, i);
+            diffuseLighting += localDiffuseLighting;
+            specularLighting += localSpecularLighting;
-            if(_LightDatas[areaIndex].lightType == GPULIGHTTYPE_LINE)
-            {
-                EvaluateBSDF_Line(  context, V, posInput, prelightData, _LightDatas[areaIndex], bsdfData,
-                                    localDiffuseLighting, localSpecularLighting);
-            }
-            else
-            {
-                EvaluateBSDF_Area(  context, V, posInput, prelightData, _LightDatas[areaIndex], bsdfData,
-                                    localDiffuseLighting, localSpecularLighting);
-            }
+            i++;
+        }
+        while (i < areaLightCount) // Rectangle lights are the last area lights so no need to check type
+        {
+            areaIndex = FetchIndex(areaLightStart, i);
+            EvaluateBSDF_Area(  context, V, posInput, prelightData, _LightDatas[areaIndex], bsdfData,
+                                localDiffuseLighting, localSpecularLighting);
+
+            i++;
         }
     }
 #endif

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

     preLightData.ggxLambdaV = GetSmithJointGGXLambdaV(NdotV, bsdfData.roughness);
 
     // GGX aniso
+    preLightData.TdotV = 0;
+    preLightData.BdotV = 0;
     if (bsdfData.materialId == MATERIALID_LIT_ANISO)
     {
         preLightData.TdotV = dot(bsdfData.tangentWS, V);