Updated HDRI sky integration

com.unity.render-pipelines.high-definition/HDRP/Sky/HDRISky/HDRISky.shader

     TEXTURE2D(_SkyIntensity);
     SAMPLER(sampler_SkyIntensity);
 
-    float4   _SkyParam; // x exposure, y multiplier, z rotation
+    float4   _SkyParam; // x exposure, y multiplier, z rotation, w lux
     float4x4 _PixelCoordToViewDirWS; // Actually just 3x3, but Unity can only set 4x4
 
     struct Attributes
         float3 rotDirY = float3(sinPhi, 0, cosPhi);
         dir = float3(dot(rotDirX, dir), dir.y, dot(rotDirY, dir));
 
-        float intensity = _SkyParam.w / SAMPLE_TEXTURE2D_LOD(_SkyIntensity, sampler_SkyIntensity, float2(.5, .5), 0).x;
+        float intensity = _SkyParam.w / SAMPLE_TEXTURE2D_LOD(_SkyIntensity, sampler_SkyIntensity, float2(0.5, 0.5), 0).x;
         float3 skyColor = ClampToFloat16Max(SAMPLE_TEXTURECUBE_LOD(_Cubemap, sampler_Cubemap, dir, 0).rgb * exp2(_SkyParam.x) * _SkyParam.y * intensity);
         return float4(skyColor, 1.0);
     }

com.unity.render-pipelines.high-definition/HDRP/Sky/HDRISky/IntegrateHDRISky.shader

             }
             
 
-real IntegrateHDRISky(TEXTURECUBE_ARGS(skybox, sampler_skybox), real3 N, uint sampleCount = 8192)
-{
-    real acc      = 0.0;
+            real IntegrateHDRISky(TEXTURECUBE_ARGS(skybox, sampler_skybox), real3 N, uint sampleCount = 8192)
+            {
+                real acc      = 0.0;
-    // Add some jittering on Hammersley2d
-    real2 randNum  = InitRandom(0.5);
+                // Add some jittering on Hammersley2d
+                real2 randNum  = InitRandom(0.5);
-    real3x3 localToWorld = GetLocalFrame(N);
+                real3x3 localToWorld = GetLocalFrame(N);
-    for (uint i = 0; i < sampleCount; ++i)
-    {
-        real2 u = frac(randNum + Hammersley2d(i, sampleCount));
+                for (uint i = 0; i < sampleCount; ++i)
+                {
+                    real2 u = frac(randNum + Hammersley2d(i, sampleCount));
-        real NdotL;
-        real weightOverPdf;
-        real3 L;
-        
-        ImportanceSampleLambert(u, localToWorld, L, NdotL, weightOverPdf);
-        real val = Luminance(SAMPLE_TEXTURECUBE_LOD(skybox, sampler_skybox, L, 0).rgb);
-        acc += NdotL * val;
-    }
+                    real NdotL;
+                    real weightOverPdf;
+                    real3 L;
+                    
+                    ImportanceSampleLambert(u, localToWorld, L, NdotL, weightOverPdf);
+                    real val = Luminance(SAMPLE_TEXTURECUBE_LOD(skybox, sampler_skybox, L, 0).rgb);
+                    acc += PI * val;
+                }
-    return acc / sampleCount;
-}
+                return acc / sampleCount;
+            }
-                float3 N = float3(0.0, 0.0, 1.0);
+                float3 N = float3(0.0, -1.0, 0.0);
 
                 float intensity = IntegrateHDRISky(TEXTURECUBE_PARAM(_Cubemap, s_trilinear_clamp_sampler), N);