Mirror Example broken on iOS 15.4

[bunnybones1]

Describe the bug

The mirror example does not render correctly on Safari in iOS 15.4 when "WebGL via Metal" is enabled (default).

We're letting WebKit devs know as well. Thought it would be useful for them and you to see if changes to the way that WebGL calls are executed can help smooth over this regression.

https://bugs.webkit.org/show_bug.cgi?id=237906

To Reproduce

Steps to reproduce the behaviour:

1. Go to https://threejs.org/examples/webgl_mirror.html
2. Rotate the view to see an odd piece of geometry stuck to the screen

Screenshots

Platform:

• Device: iPhone Xs
• OS: iOS 15.4
• Browser: Safari
• Three.js version: r138

[deltakosh]

Welcome onboard, it seems to be a wide spread issue.

[bunnybones1]

Hey,
Yeah, it's a wild day. Some instances of the bug can be worked around by disabling "WebGL via Metal", but in our project, Skyweaver, we do some more complicated offscreen renders between frames that aren't fix by doing this.

[Mugen87]

Should be fixed with the recently published iOS 15.5.