218305 2020-10-28 13:12:46 -0700 WebGL context remains in memory after calling loseContext() 2026-02-26 05:34:40 -0800 1 1 1 Unclassified WebKit WebGL Safari 14 Unspecified Unspecified NEW InRadar P2 Normal --- 1 philipbell webkit-unassigned alex dino jdarpinian kbr kkinnunen maggotfish noam smoley takashi.th.hasegawa webkit-bug-importer oldest_to_newest 1702467 0 philipbell 2020-10-28 13:12:46 -0700 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 1702935 1 smoley 2020-10-29 18:04:48 -0700 Thanks for filing! Apple Internal see rdar://35920437. 1702943 2 webkit-bug-importer 2020-10-29 18:35:13 -0700 <rdar://problem/70838378> 1704062 3 philipbell 2020-11-03 10:25:41 -0800 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 1763101 4 maggotfish 2021-05-24 05:46:05 -0700 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. 2185200 5 alex 2026-02-26 05:34:40 -0800 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/