Ported over compute shader fixes from the Unity Graphics repository:

[PPV2] PPB-6 Disabled compute effects on WebGL and Android OpenGL (#7936)

* Disabled compute based effects not supported on WebGL and Android OpenGL
* Improved editor warning messages.
* Fix editor warning messages.

com.unity.postprocessing/PostProcessing/Editor/Effects/AmbientOcclusionEditor.cs

@@ -49,8 +49,14 @@ namespace UnityEditor.Rendering.PostProcessing
             }
             else if (aoMode == (int)AmbientOcclusionMode.MultiScaleVolumetricObscurance)
             {
-                if (!SystemInfo.supportsComputeShaders)
-                    EditorGUILayout.HelpBox("Multi-scale volumetric obscurance requires compute shader support.", MessageType.Warning);
+                if (!SystemInfo.supportsComputeShaders || EditorUtilities.isTargetingWebGL)
+                {
+                    EditorGUILayout.HelpBox("Multi-scale volumetric obscurance requires compute shader support which is not available on this platform.", MessageType.Error);
+                }
+                else if(EditorUtilities.isTargetingAndroid)
+                {
+                    EditorGUILayout.HelpBox("Multi-scale volumetric obscurance requires compute shader support (Vulkan) when running on Android.", MessageType.Warning);
+                }
 
                 PropertyField(m_ThicknessModifier);
                 PropertyField(m_ZBias);

com.unity.postprocessing/PostProcessing/Editor/Effects/AutoExposureEditor.cs

@@ -31,8 +31,14 @@ namespace UnityEditor.Rendering.PostProcessing
 
         public override void OnInspectorGUI()
         {
-            if (!SystemInfo.supportsComputeShaders)
-                EditorGUILayout.HelpBox("Auto exposure requires compute shader support.", MessageType.Warning);
+            if (!SystemInfo.supportsComputeShaders || EditorUtilities.isTargetingWebGL)
+            {
+                EditorGUILayout.HelpBox("Auto exposure requires compute shader support which is not available on this platform.", MessageType.Error);
+            }
+            else if (EditorUtilities.isTargetingAndroid)
+            {
+                EditorGUILayout.HelpBox("Auto exposure requires compute shader support (Vulkan) when running on Android.", MessageType.Warning);
+            }
 
             EditorUtilities.DrawHeaderLabel("Exposure");
 

com.unity.postprocessing/PostProcessing/Editor/Utils/EditorUtilities.cs

@@ -64,6 +64,30 @@ namespace UnityEditor.Rendering.PostProcessing
             }
         }
 
+        /// <summary>
+        /// Returns <c>true</c> if the current target is Android, <c>false</c> otherwise.
+        /// </summary>
+        public static bool isTargetingAndroid
+        {
+            get
+            {
+                var t = EditorUserBuildSettings.activeBuildTarget;
+                return t == BuildTarget.Android;
+            }
+        }
+
+        /// <summary>
+        /// Returns <c>true</c> if the current target is WebGL, <c>false</c> otherwise.
+        /// </summary>
+        public static bool isTargetingWebGL
+        {
+            get
+            {
+                var t = EditorUserBuildSettings.activeBuildTarget;
+                return t == BuildTarget.WebGL;
+            }
+        }
+
         /// <summary>
         /// Returns <c>true</c> if the current target is a console or a mobile, <c>false</c>
         /// otherwise.

com.unity.postprocessing/PostProcessing/Runtime/Effects/AmbientOcclusion.cs

@@ -196,6 +196,7 @@ namespace UnityEngine.Rendering.PostProcessing
 
                 state &= SystemInfo.supportsComputeShaders
                     && !RuntimeUtilities.isAndroidOpenGL
+                    && !RuntimeUtilities.isWebGL
 #if UNITY_2023_2_OR_NEWER
                     && SystemInfo.IsFormatSupported(GraphicsFormat.R32_SFloat, GraphicsFormatUsage.Render)
                     && SystemInfo.IsFormatSupported(GraphicsFormat.R16_SFloat, GraphicsFormatUsage.Render)

com.unity.postprocessing/PostProcessing/Runtime/Effects/AutoExposure.cs

@@ -85,6 +85,7 @@ namespace UnityEngine.Rendering.PostProcessing
             return enabled.value
                 && SystemInfo.supportsComputeShaders
                 && !RuntimeUtilities.isAndroidOpenGL
+                && !RuntimeUtilities.isWebGL
                 && RenderTextureFormat.RFloat.IsSupported()
                 && context.resources.computeShaders.autoExposure
                 && context.resources.computeShaders.exposureHistogram;

com.unity.postprocessing/PostProcessing/Runtime/Monitors/Monitor.cs

@@ -48,6 +48,7 @@ namespace UnityEngine.Rendering.PostProcessing
             return requested
                 && SystemInfo.supportsComputeShaders
                 && !RuntimeUtilities.isAndroidOpenGL
+                && !RuntimeUtilities.isWebGL
                 && ShaderResourcesAvailable(context);
         }
 

com.unity.postprocessing/PostProcessing/Runtime/Utils/RuntimeUtilities.cs

@@ -858,6 +858,21 @@ namespace UnityEngine.Rendering.PostProcessing
             get { return Application.platform == RuntimePlatform.Android && SystemInfo.graphicsDeviceType != GraphicsDeviceType.Vulkan; }
         }
 
+        /// <summary>
+        /// Returns <c>true</c> if the target platform is WebGL,
+        /// <c>false</c> otherwise.
+        /// </summary>
+        public static bool isWebGL
+        {
+            get {
+#if UNITY_WEBGL
+                return true;
+#else
+                return false;
+#endif
+            }
+        }
+
         /// <summary>
         /// Gets the default HDR render texture format for the current target platform.
         /// </summary>