fix texture lod selection for clustered decals

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Decal/DecalSystem.cs

 {
     public class DecalSystem
     {
-        public const int kInvalidIndex = -1;  
+        public const int kInvalidIndex = -1;
+        public const int kDecalAtlasSize = 128;
 
         public class DecalHandle
         {
                 if (m_DecalAtlas == null)
                 {
                     m_DecalAtlas = new TextureCache2D("DecalAtlas");
-                    m_DecalAtlas.AllocTextureArray(2048, 128, 128, TextureFormat.RGBA32, true);
+                    m_DecalAtlas.AllocTextureArray(2048, kDecalAtlasSize, kDecalAtlasSize, TextureFormat.ARGB32, true);
                 }
                 return m_DecalAtlas;
             }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/HDStringConstants.cs

         public static readonly int _IrradianceSource               = Shader.PropertyToID("_IrradianceSource");
 
         public static readonly int _EnableDBuffer = Shader.PropertyToID("_EnableDBuffer");
+        public static readonly int _DecalAtlasResolution = Shader.PropertyToID("_DecalAtlasResolution");
 
         public static readonly int[] _GBufferTexture =
         {

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Decal/DBufferManager.cs

             if (frameSettings.enableDBuffer)
             {
                 cmd.SetGlobalInt(HDShaderIDs._EnableDBuffer, vsibleDecalCount > 0 ? 1 : 0);
+                cmd.SetGlobalVector(HDShaderIDs._DecalAtlasResolution, new Vector2(DecalSystem.kDecalAtlasSize, DecalSystem.kDecalAtlasSize));
                 BindBufferAsTextures(cmd);
             }
             else

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Decal/Decal.hlsl

 
 CBUFFER_START(UnityDecalParameters)
 	uint _EnableDBuffer;
+	float2 _DecalAtlasResolution;
 CBUFFER_END
 
 UNITY_INSTANCING_BUFFER_START(Decal)      

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Decal/DecalUtilities.hlsl

 			int diffuseIndex = decalData.normalToWorld[1][3];
 			int normalIndex = decalData.normalToWorld[2][3];
 			int maskIndex = decalData.normalToWorld[3][3];
-			float lod = ComputeTextureLOD(positionDS.xz);
-			if((all(positionDS.xyz > 0.0f) && all(1.0f - positionDS.xyz > 0.0f))) // clip to decal space
+			float lod = ComputeTextureLOD(positionDS.xz, _DecalAtlasResolution);								
+			decalBlend = ((all(positionDS.xyz > 0.0f) && all(1.0f - positionDS.xyz > 0.0f))) ? decalBlend : 0;	// use blend of 0 instead of an 'if' because compiler moves the lod calculation inside the 'if' which causes incorrect values if any of the pixels in the 2x2 quad gets rejected
+
+			if(diffuseIndex != -1)
-				if(diffuseIndex != -1)
-				{
-					ApplyBlendDiffuse(DBuffer0, mask, positionDS.xz, diffuseIndex, DBUFFERHTILEBIT_DIFFUSE, decalBlend, lod);
-				}
+				ApplyBlendDiffuse(DBuffer0, mask, positionDS.xz, diffuseIndex, DBUFFERHTILEBIT_DIFFUSE, decalBlend, lod);
+			}
-				if(normalIndex != -1)
-				{
-					ApplyBlendNormal(DBuffer1, mask, positionDS.xz, normalIndex, DBUFFERHTILEBIT_NORMAL, (float3x3)decalData.normalToWorld, decalBlend, lod);
-				}
+			if(normalIndex != -1)
+			{
+				ApplyBlendNormal(DBuffer1, mask, positionDS.xz, normalIndex, DBUFFERHTILEBIT_NORMAL, (float3x3)decalData.normalToWorld, decalBlend, lod);
+			}
-				if(maskIndex != -1)
-				{
-					ApplyBlendMask(DBuffer2, mask, positionDS.xz, maskIndex, DBUFFERHTILEBIT_MASK, decalBlend, lod);
-				}
+			if(maskIndex != -1)
+			{
+				ApplyBlendMask(DBuffer2, mask, positionDS.xz, maskIndex, DBUFFERHTILEBIT_MASK, decalBlend, lod);
 			}
 		}
 #else