[Port] [6000.4] [XR] Fix missing unity_StereoEyeIndex constant in URP Multi-pass, needed for stereoscopic panoramic skyboxes

Author: NetteVI

Packages/com.unity.render-pipelines.core/Runtime/XR/XRBuiltinShaderConstants.cs

@@ -52,6 +52,11 @@ public static class XRBuiltinShaderConstants
         /// </summary>
         static public readonly int unity_StereoWorldSpaceCameraPos = Shader.PropertyToID("unity_StereoWorldSpaceCameraPos");
 
+        /// <summary>
+        /// Cached unique id for unity_StereoEyeIndex
+        /// </summary>
+        static public readonly int unity_StereoEyeIndex = Shader.PropertyToID("unity_StereoEyeIndex");
+
         // Pre-allocate arrays to avoid GC
         static Matrix4x4[] s_cameraProjMatrix = new Matrix4x4[2];
         static Matrix4x4[] s_invCameraProjMatrix = new Matrix4x4[2];

Packages/com.unity.render-pipelines.universal/Runtime/ScriptableRenderer.cs

@@ -224,6 +224,10 @@ void SetPerCameraShaderVariables(RasterCommandBuffer cmd, UniversalCameraData ca
                 cameraHeight = (float)cameraTargetSizeCopy.y;
 
                 useRenderPassEnabled = false;
+                
+                // Multi-pass needs to set unity_StereoEyeIndex builtin param for skybox-panoramic.shader to work correctly (UUM-120719)
+                if (!cameraData.xr.singlePassEnabled)
+                    cmd.SetGlobalVector(XRBuiltinShaderConstants.unity_StereoEyeIndex, new Vector4(cameraData.xr.multipassId, 0, 0, 0));
             }
 
             if (camera.allowDynamicResolution)