Help Fluid not rendering on VR (URP) with single-pass stereo

[arrnav96]

Solved!

What worked for me was to set the stereo render mode from class OpenXRSettings (UnityEngine.XR.Management and UnityEngine.XR.OpenXR assemblies) on runtime, courtesy of Virtual Method's support and a helpful post from another forum.

I simply switch to Multi-pass when fluid rendering is needed/visible in my scene, then switch back to single-pass instanced using event calls when done. Works great on my Quest 3 standalone  URP build on Unity 2022.3.36f1.

Code:

public class VRRenderModeSwitcher : MonoBehaviour
{
    [SerializeField] private GameObject[] multiPassCams;
    [SerializeField] private GameObject singlePassInstancedCam;

    public void SwitchToSinglePassInstanced() => SwitchMode(OpenXRSettings.RenderMode.SinglePassInstanced);

    public void SwitchToMultiPass() => SwitchMode(OpenXRSettings.RenderMode.MultiPass);

    private void SwitchMode(OpenXRSettings.RenderMode newMode) => StartCoroutine(SwitchModeCoroutine(newMode));
       
    private IEnumerator SwitchModeCoroutine(OpenXRSettings.RenderMode newMode)
    {
        var openXRSettings = OpenXRSettings.Instance;
        openXRSettings.renderMode = newMode;
        yield return XRGeneralSettings.Instance.Manager.InitializeLoader();
    }
}

Also, for performance reasons, I additionally ended up enabling or disabling the 'ObiFluidRendererFeature' in my renderer asset on runtime as well, using the same event calls as above to enable/disable Obi rendering when needed. Below code uses reflections and is a hacky way to set renderer features, but it's the only way I found which works on current URP. This greatly boosts performance on standalone when fluid is not used:

Code:

public class SetUrpRenderFeature : MonoBehaviour
{
    [SerializeField] private string rendererFeatureNameToLookup;
       
    private static List<ScriptableRendererFeature> _rendererFeatures;

    private void Awake() => _rendererFeatures = GetRendererFeatures();

    private static List<ScriptableRendererFeature> GetRendererFeatures() {
        var renderer = (GraphicsSettings.currentRenderPipeline as UniversalRenderPipelineAsset)?.scriptableRenderer;
        return typeof(ScriptableRenderer)
            .GetField("m_RendererFeatures", BindingFlags.NonPublic | BindingFlags.Instance)
            ?.GetValue(renderer) as List<ScriptableRendererFeature>;
    }

    public void EnableRendererFeature(bool enable)
    {
        foreach (var rendererFeature in _rendererFeatures
                     .Where(rendererFeature => rendererFeature.name == rendererFeatureNameToLookup))
        {
            rendererFeature.SetActive(enable);
            return;
        }
    }
}