[2021.2 Backport] Fix for Volume Updates

com.unity.render-pipelines.universal/Runtime/UniversalAdditionalCameraData.cs

@@ -111,11 +111,14 @@ public static void SetVolumeFrameworkUpdateMode(this Camera camera, VolumeFramew
                 return;
             }
 
+            bool requiredUpdatePreviously = cameraData.requiresVolumeFrameworkUpdate;
             cameraData.volumeFrameworkUpdateMode = mode;
 
             // We only update the local volume stacks for cameras set to ViaScripting.
             // Otherwise it will be updated in every frame.
-            if (!cameraData.requiresVolumeFrameworkUpdate)
+            // We also check the previous value to make sure we're not updating when
+            // switching between Camera ViaScripting and the URP Asset set to ViaScripting
+            if (requiredUpdatePreviously && !cameraData.requiresVolumeFrameworkUpdate)
             {
                 camera.UpdateVolumeStack(cameraData);
             }
@@ -161,6 +164,27 @@ public static void UpdateVolumeStack(this Camera camera, UniversalAdditionalCame
             VolumeManager.instance.Update(cameraData.volumeStack, trigger, layerMask);
         }
 
+        /// <summary>
+        /// Destroys the volume stack for this camera.
+        /// </summary>
+        /// <param name="camera"></param>
+        public static void DestroyVolumeStack(this Camera camera)
+        {
+            UniversalAdditionalCameraData cameraData = camera.GetUniversalAdditionalCameraData();
+            camera.DestroyVolumeStack(cameraData);
+        }
+
+        /// <summary>
+        /// Destroys the volume stack for this camera.
+        /// </summary>
+        /// <param name="camera"></param>
+        /// <param name="cameraData"></param>
+        public static void DestroyVolumeStack(this Camera camera, UniversalAdditionalCameraData cameraData)
+        {
+            cameraData.volumeStack.Dispose();
+            cameraData.volumeStack = null;
+        }
+
         /// <summary>
         /// Returns the mask and trigger assigned for volumes on the camera.
         /// </summary>

com.unity.render-pipelines.universal/Runtime/UniversalRenderPipeline.cs

@@ -664,6 +664,15 @@ static void UpdateVolumeFramework(Camera camera, UniversalAdditionalCameraData a
             }
 
             // When we want to update the volumes every frame...
+
+            // We destroy the volumeStack in the additional camera data, if present, to make sure
+            // it gets recreated and initialized if the update mode gets later changed to ViaScripting...
+            if (additionalCameraData && additionalCameraData.volumeStack != null)
+            {
+                camera.DestroyVolumeStack(additionalCameraData);
+            }
+
+            // Get the mask + trigger and update the stack
             camera.GetVolumeLayerMaskAndTrigger(additionalCameraData, out LayerMask layerMask, out Transform trigger);
             VolumeManager.instance.ResetMainStack();
             VolumeManager.instance.Update(trigger, layerMask);