301627 2025-10-29 08:14:16 -0700 [WebGPU] Canvas flickers while rendering WebGPU game 2026-03-26 09:51:20 -0700 1 1 1 Unclassified WebKit WebGPU Safari 26 iPhone / iPad iOS 26 RESOLVED DUPLICATE 302711 InRadar P2 Blocker --- 1 ashley webkit-unassigned ahmad.saleem792 drew lingcherd_ho mwyrzykowski tzagallo webkit-bug-importer oldest_to_newest 2154967 0 ashley 2025-10-29 08:14:16 -0700 Safari on iOS 26 adds support for WebGPU. We now use this in our browser-based game engine Construct (https://www.construct.net). However whe rendering with WebGPU, the canvas appears to flicker, as if it is becoming invisible for some frames. This makes WebGPU unusable in Safari. Reproduction links: WebGPU demo: https://downloads.scirra.com/labs/bugs/flying-along/webgpu/ WebGL demo: https://downloads.scirra.com/labs/bugs/flying-along/webgl/ Just tap and hold to move the pig. Observe the rendering. Try starting in portrait orientation. Expected result: Smooth rendering with WebGPU as it does with WebGL. Observed result: when using WebGPU only, the entire canvas flickers. Sometimes it settles down after a few seconds and stops, but in other cases it flickers continuously. If it settles down, reloading the page usually reproduces it again. This reproduces in Safari on iOS 26.0.1 on an iPhone 12 Pro Max. 2154987 1 webkit-bug-importer 2025-10-29 09:27:19 -0700 <rdar://problem/163647932> 2154988 2 mwyrzykowski 2025-10-29 09:28:12 -0700 Seems ok on Safari Technology Preview 230. Going to check on iPhone 2154989 3 mwyrzykowski 2025-10-29 09:29:43 -0700 Reproduces on iPhone 2154990 4 mwyrzykowski 2025-10-29 09:29:54 -0700 going to try with ToT WebKit 2155003 5 mwyrzykowski 2025-10-29 10:02:26 -0700 This seems fixed on ToT WebKit 2155004 6 mwyrzykowski 2025-10-29 10:03:00 -0700 Possibly fixed by https://commits.webkit.org/302128@main 2155005 7 mwyrzykowski 2025-10-29 10:03:22 -0700 Going to confirm that was the commit which fixed the issue 2155034 8 mwyrzykowski 2025-10-29 11:21:30 -0700 I can still reproduce on 302212@main so I don't think its related 2167767 9 drew 2025-12-22 07:07:38 -0800 When I encountered the same problem on a different engine, I eventually uncovered two causes. May not be your particular causes, but typical "why does my custom engine flicker only on Safari" problems. 1. requestAnimationFrame. In particular, you want to a) call it at all, b) inside that callback produce a frame synchronously, which can be nontrivial to do with async WebGPU APIs, c) profile your calls and callbacks to ensure you're not encountering queueing delay, d) but also expect pretty much fixed 16ms vsync delay on WebKit. 2. The callback GPUQueue: onSubmittedWorkDone() arrives for me in roughly 32ms (2 v-sycs) which tends to be later than some other browsers. If you are like me and ran the napkin math on "obviously we can do a trivial GPU pass in a few ms) you may want to consider if this is the source of the flicker. 2170216 10 ashley 2026-01-08 03:32:58 -0800 This issue still reproduces for me in Safari 26.2. It makes WebGPU completely unusable, and so we're going to have to disable WebGPU entirely on iOS and fall back to WebGL rendering only for the time being. FWIW our engine does already synchronously render in requestAnimationFrame and does not rely on onSubmittedWorkDone. 2170217 11 ashley 2026-01-08 03:37:48 -0800 It looks like the issue also reproduces in Safari 26.2 on macOS, which means WebGPU is currently completely unusable for us on all Apple platforms. 2170221 12 ahmad.saleem792 2026-01-08 03:41:20 -0800 (In reply to Ashley Gullen from comment #11) > It looks like the issue also reproduces in Safari 26.2 on macOS, which means > WebGPU is currently completely unusable for us on all Apple platforms. Can you share macOS hardware details? Apple Silicon M1 etc? It would be good to know. 2170307 13 mwyrzykowski 2026-01-08 08:43:09 -0800 This might be fixed on WebKit main. I don’t reproduce on my iPhone Air with ToT WebKit when viewing https://downloads.scirra.com/labs/bugs/flying-along/webgpu/ 2170308 14 mwyrzykowski 2026-01-08 08:43:26 -0800 Going to try some other devices to be sure 2170328 15 mwyrzykowski 2026-01-08 09:39:37 -0800 I’m able to reproduce on an iPhone 13 Mini on shipping iOS 26.2 2170352 16 mwyrzykowski 2026-01-08 11:07:47 -0800 Installing ToT webkit on the iPhone 13 mini and I don't reproduce. To fully close out this bug we should bisect from 26.2 and dupe to the change which resolved this 2170380 18 mwyrzykowski 2026-01-08 12:26:39 -0800 *** This bug has been marked as a duplicate of bug 302711 *** 2181279 19 ashley 2026-02-13 07:04:06 -0800 This still reproduces for me on macOS, iPadOS and iOS 26.3. I don't know if the fix for this is meant to be in that release. Should I file a new issue? 2181361 20 mwyrzykowski 2026-02-13 09:59:01 -0800 Sorry my wording was potentially confusing. There was a bug fix after 26.2 https://bugs.webkit.org/show_bug.cgi?id=302711 which addressed this. It is only in STP right now. I will update you when it’s in a public beta of iOS. 2182126 21 mwyrzykowski 2026-02-16 10:57:13 -0800 Thanks again for the bug report, I just wanted to let you know this should be resolved in beta 1 of iOS 26.4 which is now available to developers. 2193984 22 ashley 2026-03-26 09:49:34 -0700 Looks like it's working correctly in Safari 26.4 now. Thanks for the fix. 2193985 23 mwyrzykowski 2026-03-26 09:51:20 -0700 That’s great! Thank you for confirming