[Unity6][URP] Make sure we only allocate shadow textures when needed (UUM-70142)

Fixes UUM-70142.
The issue is that the constructor was allocating shadow maps, which caused memory leakage when switching between graphics quality. This PR changes it so the textures are only allocated when needed and with a check for if it has already been created.

Author: ellioman

Packages/com.unity.render-pipelines.universal/Runtime/Passes/AdditionalLightsShadowCasterPass.cs

@@ -39,7 +39,8 @@ private static class AdditionalShadowsConstantBuffer
         private bool m_EmptyShadowmapNeedsClear = false;
         private RTHandle m_EmptyAdditionalLightShadowmapTexture;
         private const int k_EmptyShadowMapDimensions = 1;
-        private const string k_EmptyShadowMapName = "_EmptyAdditionalLightShadowmapTexture";
+        private const string k_AdditionalLightShadowMapTextureName = "_AdditionalLightsShadowmapTexture";
+        private const string k_EmptyAdditionalLightShadowMapTextureName = "_EmptyAdditionalLightShadowmapTexture";
         internal static Vector4[] s_EmptyAdditionalLightIndexToShadowParams = null;
 
         float m_MaxShadowDistanceSq;
@@ -78,7 +79,7 @@ public AdditionalLightsShadowCasterPass(RenderPassEvent evt)
             AdditionalShadowsConstantBuffer._AdditionalShadowOffset1 = Shader.PropertyToID("_AdditionalShadowOffset1");
             AdditionalShadowsConstantBuffer._AdditionalShadowFadeParams = Shader.PropertyToID("_AdditionalShadowFadeParams");
             AdditionalShadowsConstantBuffer._AdditionalShadowmapSize = Shader.PropertyToID("_AdditionalShadowmapSize");
-            m_AdditionalLightsShadowmapID = Shader.PropertyToID("_AdditionalLightsShadowmapTexture");
+            m_AdditionalLightsShadowmapID = Shader.PropertyToID(k_AdditionalLightShadowMapTextureName);
 
             m_AdditionalLightsWorldToShadow_SSBO = Shader.PropertyToID("_AdditionalLightsWorldToShadow_SSBO");
             m_AdditionalShadowParams_SSBO = Shader.PropertyToID("_AdditionalShadowParams_SSBO");
@@ -108,7 +109,6 @@ public AdditionalLightsShadowCasterPass(RenderPassEvent evt)
                 m_AdditionalLightShadowSliceIndexTo_WorldShadowMatrix = new Matrix4x4[maxVisibleAdditionalLights];
             }
 
-            m_EmptyAdditionalLightShadowmapTexture = ShadowUtils.AllocShadowRT(k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_ShadowmapBufferBits, 1, 0, name: k_EmptyShadowMapName);
             m_EmptyShadowmapNeedsClear = true;
         }
 
@@ -576,7 +576,7 @@ public bool Setup(UniversalRenderingData renderingData, UniversalCameraData came
                 m_AdditionalLightShadowSliceIndexTo_WorldShadowMatrix[globalShadowSliceIndex] = sliceTransform * m_AdditionalLightShadowSliceIndexTo_WorldShadowMatrix[globalShadowSliceIndex];
             }
 
-            ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_AdditionalLightsShadowmapHandle, renderTargetWidth, renderTargetHeight, k_ShadowmapBufferBits, name: "_AdditionalLightsShadowmapTexture");
+            ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_AdditionalLightsShadowmapHandle, renderTargetWidth, renderTargetHeight, k_ShadowmapBufferBits, name: k_AdditionalLightShadowMapTextureName);
 
             m_MaxShadowDistanceSq = cameraData.maxShadowDistance * cameraData.maxShadowDistance;
             m_CascadeBorder = shadowData.mainLightShadowCascadeBorder;
@@ -596,7 +596,7 @@ bool SetupForEmptyRendering(bool stripShadowsOffVariants, UniversalShadowData sh
             useNativeRenderPass = false;
 
             // Required for scene view camera(URP renderer not initialized)
-            if (ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_EmptyAdditionalLightShadowmapTexture, k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_ShadowmapBufferBits, name: k_EmptyShadowMapName))
+            if (ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_EmptyAdditionalLightShadowmapTexture, k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_ShadowmapBufferBits, name: k_EmptyAdditionalLightShadowMapTextureName))
                 m_EmptyShadowmapNeedsClear = true;
 
             // initialize _AdditionalShadowParams

Packages/com.unity.render-pipelines.universal/Runtime/Passes/MainLightShadowCasterPass.cs

@@ -32,9 +32,10 @@ private static class MainLightShadowConstantBuffer
 
         int m_MainLightShadowmapID;
         internal RTHandle m_MainLightShadowmapTexture;
-        private RTHandle m_EmptyLightShadowmapTexture;
+        private RTHandle m_EmptyMainLightShadowmapTexture;
         private const int k_EmptyShadowMapDimensions = 1;
-        private const string k_EmptyShadowMapName = "_EmptyLightShadowmapTexture";
+        private const string k_MainLightShadowMapTextureName = "_MainLightShadowmapTexture";
+        private const string k_EmptyMainLightShadowMapTextureName = "_EmptyMainLightShadowmapTexture";
         private static readonly Vector4 s_EmptyShadowParams = new Vector4(1, 0, 1, 0);
         private static readonly Vector4 s_EmptyShadowmapSize = s_EmptyShadowmapSize = new Vector4(k_EmptyShadowMapDimensions, 1f / k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions);
 
@@ -76,9 +77,7 @@ public MainLightShadowCasterPass(RenderPassEvent evt)
             MainLightShadowConstantBuffer._ShadowOffset1 = Shader.PropertyToID("_MainLightShadowOffset1");
             MainLightShadowConstantBuffer._ShadowmapSize = Shader.PropertyToID("_MainLightShadowmapSize");
 
-            m_MainLightShadowmapID = Shader.PropertyToID("_MainLightShadowmapTexture");
-
-            m_EmptyLightShadowmapTexture = ShadowUtils.AllocShadowRT(k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_ShadowmapBufferBits, 1, 0, name: k_EmptyShadowMapName);
+            m_MainLightShadowmapID = Shader.PropertyToID(k_MainLightShadowMapTextureName);
             m_EmptyShadowmapNeedsClear = true;
         }
 
@@ -88,7 +87,7 @@ public MainLightShadowCasterPass(RenderPassEvent evt)
         public void Dispose()
         {
             m_MainLightShadowmapTexture?.Release();
-            m_EmptyLightShadowmapTexture?.Release();
+            m_EmptyMainLightShadowmapTexture?.Release();
         }
 
         /// <summary>
@@ -141,8 +140,7 @@ public bool Setup(UniversalRenderingData renderingData, UniversalCameraData came
                 Debug.LogWarning("Only directional lights are supported as main light.");
             }
 
-            Bounds bounds;
-            if (!renderingData.cullResults.GetShadowCasterBounds(shadowLightIndex, out bounds))
+            if (!renderingData.cullResults.GetShadowCasterBounds(shadowLightIndex, out Bounds _))
                 return SetupForEmptyRendering(cameraData.renderer.stripShadowsOffVariants);
 
             m_ShadowCasterCascadesCount = shadowData.mainLightShadowCascadesCount;
@@ -161,7 +159,7 @@ public bool Setup(UniversalRenderingData renderingData, UniversalCameraData came
                     return SetupForEmptyRendering(cameraData.renderer.stripShadowsOffVariants);
             }
 
-            ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_MainLightShadowmapTexture, renderTargetWidth, renderTargetHeight, k_ShadowmapBufferBits, name: "_MainLightShadowmapTexture");
+            ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_MainLightShadowmapTexture, renderTargetWidth, renderTargetHeight, k_ShadowmapBufferBits, name: k_MainLightShadowMapTextureName);
 
             m_MaxShadowDistanceSq = cameraData.maxShadowDistance * cameraData.maxShadowDistance;
             m_CascadeBorder = shadowData.mainLightShadowCascadeBorder;
@@ -180,7 +178,7 @@ bool SetupForEmptyRendering(bool stripShadowsOffVariants)
             useNativeRenderPass = false;
 
             // Required for scene view camera(URP renderer not initialized)
-            if(ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_EmptyLightShadowmapTexture, k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_ShadowmapBufferBits, name: k_EmptyShadowMapName))
+            if(ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_EmptyMainLightShadowmapTexture, k_EmptyShadowMapDimensions, k_EmptyShadowMapDimensions, k_ShadowmapBufferBits, name: k_EmptyMainLightShadowMapTextureName))
                 m_EmptyShadowmapNeedsClear = true;
 
             return true;
@@ -197,7 +195,7 @@ public override void Configure(CommandBuffer cmd, RenderTextureDescriptor camera
             #pragma warning disable CS0618
             if (m_CreateEmptyShadowmap)
             {
-                ConfigureTarget(m_EmptyLightShadowmapTexture);
+                ConfigureTarget(m_EmptyMainLightShadowmapTexture);
                 m_EmptyShadowmapNeedsClear = false;
             }
             else
@@ -220,8 +218,7 @@ public override void Execute(ScriptableRenderContext context, ref RenderingData
             if (m_CreateEmptyShadowmap)
             {
                 SetEmptyMainLightCascadeShadowmap(CommandBufferHelpers.GetRasterCommandBuffer(universalRenderingData.commandBuffer));
-                universalRenderingData.commandBuffer.SetGlobalTexture(m_MainLightShadowmapID, m_EmptyLightShadowmapTexture.nameID);
-
+                universalRenderingData.commandBuffer.SetGlobalTexture(m_MainLightShadowmapID, m_EmptyMainLightShadowmapTexture.nameID);
                 return;
             }