[Webkit-unassigned] [Bug 245476] New: WebGL2 on IOS 16.0 crashing on glReadPixels

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=245476

            Bug ID: 245476
           Summary: WebGL2 on IOS 16.0 crashing on glReadPixels
           Product: WebKit
           Version: Safari 15
          Hardware: iPhone / iPad
                OS: iOS 16
            Status: NEW
          Severity: Major
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: george at nomitech.com
                CC: dino at apple.com, kbr at google.com, kkinnunen at apple.com

Hallo,

We have just updated to IOS 16 and found a serious issue in WebGL2 glReadPixels function call from our wasm module.
glReadPixes either crashes on bigger files or becomes very slow on smaller files. 

Everything was working nice and fast on IOS 15.5, until we updated to IOS 16.0 (and Safari 16.0 I suppose).

To reproduce the crashing issue (on IOS 16.0 only) please do as follows, for reference I have tried on iPhone 12.

1. Open this URL: https://tinyurl.com/mry9mkrj  
2. The page will load a mid-size 3D Model
3. Now try to rotate it (this will make a call to glReadPixels to get a pivot)
4. BSOD Crash: WebGL: context lost. readPixels

To reproduce the slow glReadPixels function issue (on IOS 16.0 only) please do as follows, for reference I have tried on iPhone 12.

1. Open this URL: https://tinyurl.com/2unkf9kx   
2. The page will load a small 3D Model that rotates now fast

Now we can start sending many glReadPixels to notice major drop in FPS.
To do that follow below steps:

3. Click on Pick Mode and select length
4. Use the thumb widget to measure some distance length and see how slowly it responds to glReadPixels 

Everything was working fine in IOS 15, looks like a major issue as glReadPixels is a core WebGL2 call.

Thanks

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