[ReflectionProbeEditor] Support for realtime probe

ScriptableRenderPipeline/HDRenderPipeline/Editor/Lighting/HDCubemapInspector.cs

 
     public override void OnPreviewSettings()
     {
+        var mipmapCount = 0;
+        var cubemap = target as Cubemap;
+        var rt = target as RenderTexture;
+        if (cubemap != null)
+            mipmapCount = cubemap.mipmapCount;
+        if (rt != null)
+            mipmapCount = rt.useMipMap
+                ? (int)(Mathf.Log(Mathf.Max(rt.width, rt.height)) / Mathf.Log(2))
+                : 1;
+
         GUI.enabled = true;
 
         GUILayout.Box(s_ExposureLow, s_PreLabel, GUILayout.MaxWidth(20));
         GUILayout.Box(s_MipMapHigh, s_PreLabel, GUILayout.MaxWidth(20));
         GUI.changed = false;
-        mipLevelPreview = GUILayout.HorizontalSlider(mipLevelPreview, 0, ((Cubemap)target).mipmapCount, GUILayout.MaxWidth(80));
+        mipLevelPreview = GUILayout.HorizontalSlider(mipLevelPreview, 0, mipmapCount, GUILayout.MaxWidth(80));
         GUILayout.Box(s_MipMapLow, s_PreLabel, GUILayout.MaxWidth(20));
     }
 
         m_PreviewUtility.camera.farClipPlane = 20.0f;
         m_PreviewUtility.camera.transform.position = new Vector3(0, 0, 2);
         m_PreviewUtility.camera.transform.LookAt(Vector3.zero);
-        //m_PreviewUtility.camera.clearFlags = CameraClearFlags.Skybox;
     }
 
     bool HandleMouse(Rect Viewport)

ScriptableRenderPipeline/HDRenderPipeline/Editor/Lighting/HDReflectionProbeEditor.Preview.cs

             if (ValidPreviewSetup())
             {
                 Editor editor = m_CubemapEditor;
-                CreateCachedEditor(((ReflectionProbe)target).texture, null, ref editor);
+                CreateCachedEditor(((ReflectionProbe)target).texture, typeof(HDCubemapInspector), ref editor);
                 m_CubemapEditor = editor as HDCubemapInspector;
             }