Warnings in console on Quest when WebXR layers are enabled.

Describe the bug

WebGL: INVALID_OPERATION: drawBuffers: COLOR_ATTACHMENTi_EXT or NONE warning each frame when WebXR layers are enabled.

To Reproduce

Steps to reproduce the behavior:

1. Use an Oculus Quest with WebXR layers enabled
2. Attach a Chrome debugger to the Quest browser
3. Go to https://threejs.org/examples/?q=layer#webxr_vr_layers and enter VR
4. See warnings in log followed by WebGL: too many errors, no more errors will be reported to the console for this context.

Code

I’m not familiar enough with Three.js to submit a fix for this, but I tracked down the issue to WebGLRenderer.js. If you add if (!xr.isPresenting) { around the code that sets _currentDrawBuffers[ 0 ] = _gl.BACK;, the warnings go away. This call interferes with the gl.framebufferTexture2D( gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0,... ); in WebXRManager. Ideally, the check would be something like if (!xr.isPresenting || !areWebXrLayersEnabled) , but I’m not sure what cleanest way is for determining if XR layers enabled in that class.

Platform:

• Device: Quest 2
• OS: oculus/hollywood/hollywood:10/QQ3A.200805.001/17007100222900000:user/release-keys
• Browser: Mozilla/5.0 (X11; Linux x86_64; Quest 2) AppleWebKit/537.36 (KHTML, like Gecko) OculusBrowser/16.1.0.3.48.300946211 SamsungBrowser/4.0 Chrome/91.0.4472.114 Safari/537.36
• Three.js version: r130

[cabanier]

@mrdoob #22558 will fix this issue. Who would be best to look at this change? I had a couple of people look at it internally but they are not as familiar with three.

[klausw]

I investigated this as part of https://github.com/google/model-viewer/discussions/2769#discussioncomment-1307863 , it also happens in <model-viewer> when rendering shadows.

If I’m understanding it right, the problem is that GL_BACK is only valid for drawBuffers when using the default framebuffer. However, state.bindFramebuffer(…, null) has an override to use the XR opaque framebuffer instead of the default framebuffer, and that’s a bound FBO for which GL_BACK is not valid.