Troubleshooting

The following sections provide troubleshooting tips for various common situations:

Ensure that the shader used for transparent objects sets up alpha blending correctly to work with Passthrough compositing. A typical pitfall uses joint blend factors for color and alpha (e.g., Blend SrcAlpha OneMinusSrcAlpha). This combination causes the src alpha value to be squared and decreases the alpha values in the framebuffer. The fix uses separate blend factors (e.g., Blend SrcAlpha OneMinusSrcAlpha, One OneMinusSrcAlpha).

The XR Compositor discards fragments that have an alpha value of 0. Some shaders do not write an alpha value into the framebuffer, for example, because of a color mask (ColorMask RGB). Such materials may still appear on top of opaque VR objects but not over the background/Passthrough. Ensure that your shaders emit a non-zero alpha value and that color mask and blend factors allow the alpha value to propagate to the framebuffer (e.g., by removing ColorMask statements from the shader).

When switching between scenes that both utilize active Passthrough layers, you may notice some flickering. This flickering occurs because the Passthrough layer is recreated with each scene load, leading to noticeable transitions. To mitigate this issue, the Passthrough layer can be made persistent across scenes by marking it with Unity’s DontDestroyOnLoad API. This ensures that the Passthrough layer is not destroyed and instead continues to exist across different scenes. It is recommended to disable and then re-enable the persistent Passthrough layer as needed, rather than destroying and recreating it. This approach helps maintain a smooth and seamless Passthrough experience during scene transitions.