Bug 218305 – WebGL context remains in memory after calling loseContext()

• Status: NEW
• Component: WebGL

[Philip]

To reproduce: 
Create over 16 WebGL contexts and call loseContext on each.
On the 17th call two errors will be thrown: 
> ‘There are too many active WebGL contexts on this page, the oldest context will be lost.’
> ‘WebGL: INVALID_OPERATION: loseContext: context already lost’
It's expected that these contexts would not remain in memory.

Code snippet:
for (let i = 0; i < 17; i++) {
  const canvas = document.createElement('canvas');
  const gl = canvas.getContext('webgl');  
  const extension = gl.getExtension('WEBGL_lose_context')
  extension.loseContext();
}

Example CodePen of dynamically losing & restoring contexts.
https://codepen.io/philipbell/pen/RwRQGmo

[Smoley]

Thanks for filing! Apple Internal see rdar://35920437.

[Radar WebKit Bug Importer]

<rdar://problem/70838378>

[Philip]

Some additional context:
loseContext is used in popular WebGL libraries including Three.js and PixiJS. 
Without this method their context management code fails.

Three.js manages context directly in the renderer code:
https://github.com/mrdoob/three.js/blob/3989bb4a00a9f38b1df5dc02bcbc1e5a1b80df53/src/renderers/WebGLRenderer.js#L345-L357

PixiJS has a component dedicated to context management:
https://github.com/pixijs/pixi.js/blob/9ff49a23670bdb0ed864d4e53fb91d524eab59f2/packages/core/src/context/ContextSystem.ts#L248-L262

[Yehonatan Daniv]

Looks like a duplicate of this: https://bugs.webkit.org/show_bug.cgi?id=200031
At Wix we use Kampos (https://github.com/wix/kampos), which doesn't use the WEBGL_lose_context plugin, but still getting the same error.

[Alex Suzuki]

I do not think this is related to https://bugs.webkit.org/show_bug.cgi?id=200031, which is marked as FIXED. It still reproduces for me on iOS 26.3, although I don't understand if it's just a misleading error message or an actual error.

I ran into this when benchmarking a barcode scanning library the uses WebGL to pre-process camera frames: basically a long loop that in every iteration created and released infrastructure that owns an OffscreenCanvas and WebGL context. I experienced crashes too, but those disappeared when each iteration was put into a separate turn of the event loop (i.e. each iteration wrapped in a setTimeout() invocation).

Separate reproducer (before I found this issue):
https://github.com/pixelverse-llc/ios-safari-webgl-context-not-released
GitHub pages site:
https://pixelverse-llc.github.io/ios-safari-webgl-context-not-released/