[PlanarReflection] use alpha in sample env for weight

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/LightLoopDef.hlsl

 // EnvIndex can also be use to fetch in another array of struct (to  atlas information etc...).
 // Cubemap      : texCoord = direction vector
 // Texture2D    : texCoord = projectedPositionWS - lightData.capturePosition
-float4 SampleEnv(LightLoopContext lightLoopContext, int index, float3 texCoord, float lod, out float weight)
+float4 SampleEnv(LightLoopContext lightLoopContext, int index, float3 texCoord, float lod)
 {
     // 31 bit index, 1 bit cache type
     uint cacheType = index & 1;
             float4 color = SAMPLE_TEXTURE2D_ARRAY_LOD(_Env2DTextures, s_trilinear_clamp_sampler, ndc, index, 0);
             // Discard pixels out of oblique projection
             // We only check RGB because the texture may have BC6H compression
-            weight = any(ndc < 0) || any(ndc > 1) || all(color.rgb >= 1000) ? 0 : 1;
+            color.a = any(ndc < 0) || any(ndc > 1) || all(color.rgb >= 1000) ? 0 : 1;
-            weight = 1;
-            return SAMPLE_TEXTURECUBE_ARRAY_LOD_ABSTRACT(_EnvCubemapTextures, s_trilinear_clamp_sampler, texCoord, index, lod);
+            float4 color = SAMPLE_TEXTURECUBE_ARRAY_LOD_ABSTRACT(_EnvCubemapTextures, s_trilinear_clamp_sampler, texCoord, index, lod);
+            color.a = 1;
+            return color;
-        weight = 0;
-        weight = 1;
         return SampleSkyTexture(texCoord, lod);
     }
 }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.hlsl

     float3 F = preLightData.specularFGD;
     float iblMipLevel = PerceptualRoughnessToMipmapLevel(preLightData.iblPerceptualRoughness);
 
-    float sampleWeight = 1;
-    float4 preLD = SampleEnv(lightLoopContext, lightData.envIndex, R, iblMipLevel, sampleWeight);
-    weight *= sampleWeight;
+    float4 preLD = SampleEnv(lightLoopContext, lightData.envIndex, R, iblMipLevel);
+    weight *= preLD.a;
 
     // Smooth weighting
     weight = Smoothstep01(weight);
             envLighting *= Sq(1.0 - preLightData.coatIblF);
 
             // Evaluate the Clear Coat color
-            float4 preLD = SampleEnv(lightLoopContext, lightData.envIndex, coatR, 0.0, sampleWeight);
+            float4 preLD = SampleEnv(lightLoopContext, lightData.envIndex, coatR, 0.0);
             envLighting += preLightData.coatIblF * preLD.rgb;
 
             // Can't attenuate diffuse lighting here, may try to apply something on bakeLighting in PostEvaluateBSDF

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/LitReference.hlsl

 
         if (NdotL > 0.0)
         {
-            float sampleWeight = 1;
-            float4 val = SampleEnv(lightLoopContext, lightData.envIndex, L, 0, sampleWeight);
+            float4 val = SampleEnv(lightLoopContext, lightData.envIndex, L, 0);
 
             // We don't multiply by 'bsdfData.diffuseColor' here. It's done only once in PostEvaluateBSDF().
             acc += LambertNoPI() * weightOverPdf * val.rgb;
             // in weightOverPdf of ImportanceSampleLambert call.
             float disneyDiffuse = DisneyDiffuse(NdotV, NdotL, LdotV, bsdfData.perceptualRoughness);
 
-            float sampleWeight = 1;
-            float4 val = SampleEnv(lightLoopContext, lightData.envIndex, L, 0, sampleWeight);
+            float4 val = SampleEnv(lightLoopContext, lightData.envIndex, L, 0);
             // We don't multiply by 'bsdfData.diffuseColor' here. It's done only once in PostEvaluateBSDF().
             acc += disneyDiffuse * weightOverPdf * val.rgb;
         }
             // Fresnel component is apply here as describe in ImportanceSampleGGX function
             float3 FweightOverPdf = F_Schlick(bsdfData.fresnel0, VdotH) * weightOverPdf;
 
-            float sampleWeight = 1;
-            float4 val = SampleEnv(lightLoopContext, lightData.envIndex, L, 0, sampleWeight);
+            float4 val = SampleEnv(lightLoopContext, lightData.envIndex, L, 0);
 
             acc += FweightOverPdf * val.rgb;
         }