Additive light support

ScriptableRenderPipeline/LightweightPipeline/LWRP/LightweightPipeline.cs

 
         private Vector4 kDefaultLightPosition = new Vector4(0.0f, 0.0f, 1.0f, 0.0f);
         private Vector4 kDefaultLightColor = Color.black;
-        private Vector4 kDefaultLightAttenuation = new Vector4(0.0f, 1.0f, 0.0f, 1.0f);
+
+        //TLS Note: We need to hijack alpha to easily know when we are at a spot light for some features.
+        private Vector4 kDefaultLightAttenuation = new Vector4(0.0f, 1.0f, 0.0f, 0.0f);
+        
         private Vector4 kDefaultLightSpotDirection = new Vector4(0.0f, 0.0f, 1.0f, 0.0f);
         private Vector4 kDefaultLightSpotAttenuation = new Vector4(0.0f, 1.0f, 0.0f, 0.0f);
 
                 float smoothAngleRange = Mathf.Max(0.001f, cosInnerAngle - cosOuterAngle);
                 float invAngleRange = 1.0f / smoothAngleRange;
                 float add = -cosOuterAngle * invAngleRange;
-                lightSpotAttenuation = new Vector4(invAngleRange, add, 0.0f);
+                lightSpotAttenuation = new Vector4(invAngleRange, add, 0.0f, 1f);
             }
 
             Light light = lightData.light;

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/Subsurface/Lighting.hlsl

     half3   color;
     half3   attenuation; //NOTE: RGB attenuation for shadow scatter.
     half    subtractiveModeAttenuation;
+    int     isSpot;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
     light.attenuation = directionAndRealtimeAttenuation.w;
     light.subtractiveModeAttenuation = lightInput.distanceAttenuation.w;
     light.color = lightInput.color;
+    light.isSpot = lightInput.spotAttenuation.w;
 
     return light;
 }
     light.attenuation = directionAndRealtimeAttenuation.w;
     light.subtractiveModeAttenuation = lightInput.distanceAttenuation.w;
     light.color = lightInput.color;
+    light.isSpot = lightInput.spotAttenuation.w;
 
     return light;
 }
     return volumeAlbedo * (exp(-t2 * halfRcpVariance1) * lerpWeight1 + exp(-t2 * halfRcpVariance2) * lerpWeight2);
 }
 
-half3 DiffuseScattering(BRDFData brdfData, half3 normalHighWS, half3 normalLowWS, half3 lightDirectionWS)
+half3 DiffuseScattering(BRDFData brdfData, half3 normalHighWS, half3 lightDirectionWS, half Attenuation, int isSpot)
-    NdotL = 0.5 * NdotL + 0.5; //Scale to 0..1 for lookup.
+
+    //NOTE: We need to account for spot light attenuation here.
+    float lookup = (0.5 * NdotL + 0.5) * lerp(1, 0.5 * Attenuation + 0.5, isSpot); //Scale lookup to 0..1
-    return SAMPLE_TEXTURE2D_ARRAY(_PreintegratedDiffuseScatteringTextures, sampler_PreintegratedDiffuseScatteringTextures, float2(NdotL, brdfData.curvature), _DiffusionProfile).rgb;
+    return SAMPLE_TEXTURE2D_ARRAY(_PreintegratedDiffuseScatteringTextures, sampler_PreintegratedDiffuseScatteringTextures, float2(lookup, brdfData.curvature), _DiffusionProfile).rgb;
 }
 
 half3 ShadowScattering(half shadow, half NdotL)
     return lightColor * specularReflection;
 }
 
-half3 LightingPhysicallyBased(BRDFData brdfData, half3 lightColor, half3 lightDirectionWS, half3 lightAttenuation, half3 normalWS, half3 viewDirectionWS)
+half3 LightingPhysicallyBased(BRDFData brdfData, half3 lightColor, half3 lightDirectionWS, half3 lightAttenuation, int isSpot, half3 normalWS, half3 viewDirectionWS)
-    half3 NdotL = DiffuseScattering(brdfData, normalWS, normalWS, lightDirectionWS);
+    half3 NdotL = DiffuseScattering(brdfData, normalWS, lightDirectionWS, lightAttenuation, isSpot);
     half3 radiance = lightColor * (lightAttenuation * NdotL);
     return DirectBDRF(brdfData, normalWS, lightDirectionWS, viewDirectionWS) * radiance;
 }
-    return LightingPhysicallyBased(brdfData, light.color, light.direction, light.attenuation, normalWS, viewDirectionWS);
+    return LightingPhysicallyBased(brdfData, light.color, light.direction, light.attenuation, light.isSpot, normalWS, viewDirectionWS);
 }
 
 half3 VertexLighting(float3 positionWS, half3 normalWS)