[wimp] Adds wimp-heavy variant for non-chrome browsers by gaaclarke · Pull Request #189953 · flutter/flutter

gaaclarke · 2026-07-23T21:34:16Z

This gets wimp_heavy loading on firefox. There are still some webgl errors though.

video

Before this change nothing rendered for counter, now it works as long as you don't hover over the floating button.

firefox.mov

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Code Review

This pull request introduces support for a heavy variant of the Wimp renderer, 'wimp_heavy', by updating build targets, artifact copying steps, and the Web SDK configuration. Additionally, the loader logic in 'skwasm_loader.js' is updated to resolve 'wimp_heavy' when a heavy build is required and Wimp is enabled. Feedback suggests using optional chaining on the 'config' object in the loader to prevent potential runtime errors if 'config' is undefined.

gemini-code-assist · 2026-07-23T21:35:13Z

  const needsHeavy = (!browserEnvironment.hasImageCodecs || !browserEnvironment.hasChromiumBreakIterators)
  const fileStem = needsHeavy
-     ? 'skwasm_heavy'
+     ? (config.enableWimp ? 'wimp_heavy' : 'skwasm_heavy')


To prevent potential runtime errors if the config object is null or undefined (for example, in certain test environments or custom embeddings), consider using optional chaining (config?.enableWimp) when checking the configuration.

Suggested change

? (config.enableWimp ? 'wimp_heavy' : 'skwasm_heavy')

? (config?.enableWimp ? 'wimp_heavy' : 'skwasm_heavy')

eyebrowsoffire

We will actually need some kind of solution for how to deal with image decoding. As of right now, just flipping the heavy flag just compiles in SkAnimatedImage, which will have skia do image decoding for us on non-Chrome browsers. But that just produces an SkImage, which is incompatible with wimp, and will basically cause things to crash if the web engine attempts to render an image this way.

The reason the "light" version of skwasm/wimp gets away with this is because on Chrome, all code paths on the dart side use the browser-based ImageDecoder API to produce an ImageBitmap and so the animated image path is never used. I think the newest versions of Firefox and Safari support this API now, so theoretically we could do the same there, but in practice we haven't turned that on on the dart side for browsers other than Chrome. In the past we used to feature gate things by the existence of the browser API rather than explicitly turning it on per-browser, but we got burned by that when browsers would release a buggy version of their API that we hadn't vetted yet and we were left scrambling to put a patch in to disable it.

If it turns out that both Firefox's and Safari's ImageDecoder APIs are actually ready for prime time and available in all supported versions of our browser, we could consider completely removing the SkAnimatedImage path and then it's one less vector to worry about for the heavy vs. light conversation. But we'll need to talk to the other web folks to move forward on that and make sure we change things on the dart side to always use the browser-based ImageDecoder API.

gaaclarke · 2026-07-23T22:48:19Z

@eyebrowsoffire okay, that probably explains the weird errors I've been trying to get to the bottom of.

If it turns out that both Firefox's and Safari's ImageDecoder APIs are actually ready for prime time

I don't actually think that is the case for Safari: https://developer.mozilla.org/en-US/docs/Web/API/ImageDecoder

It is an explicit omission on safari.

gaaclarke · 2026-07-23T22:50:27Z

@eyebrowsoffire I'll look into the ImageDecoder in a separate PR. This actually renders something in firefox, whereas before this it rendered nothing.

gaaclarke · 2026-07-24T18:07:00Z

@eyebrowsoffire okay, that probably explains the weird errors I've been trying to get to the bottom of.

Actually the problem was the one fixed in #189958. Firefox webgl2 is stricter in this case.

gaaclarke · 2026-07-27T20:41:10Z

Chatted with @eyebrowsoffire offline. He would like a fallback path for image decoding and enabling some felt integration tests as part of this pr.

His notes:

This is the spot in the code where we decide what kind of image decoding strategy to use: https://github.com/flutter/flutter/blob/master/engine/src/flutter/lib/web_ui/lib/src/engine/skwasm/skwasm_impl/renderer.dart#L355

We'll need some way to determine whether the underlying skwasm/wimp binary supports animated image codec, and then bail out to the dom encoder if it doesn't (which will probably just give us a still of the animated image, which seems like a pretty reasonable fallback)

As for enabling unit tests, we'll probably want to add two configs similar to this one, but one on firefox and one on safari: https://github.com/flutter/flutter/blob/master/engine/src/flutter/lib/web_ui/test/felt_config.yaml#L150
Once you've added it to felt_config.yaml you can run felt generate-builder-json and it will modify the appropriate engine_v2 json file to add the test suites to our CI runs

Also, once you've added it to felt_config.yaml you could do like felt test --suite=firefox-dart2wasm-wimp-ui to actually run the unit tests (you'll have to build wimp_heavy and all that first)

In terms of a mechanism for exposing whether the binary actually supports the animated image path, it's going to look similar to the way we expose the skwasmIsHeavy function: https://github.com/flutter/flutter/blob/master/engine/src/flutter/skwasm/text/paragraph_builder_client_icu.cc#L12

We're basically decoupling the idea of "heavy" to mean "has builtin ICU support" and "has animated image support". Previously, heavy just meant both of these, but now the wimp_heavy is going to have builtin ICU support but no animated image support.

gaaclarke · 2026-07-27T23:34:48Z

rebasing to get our opengles fix (#189958)

flutter-dashboard · 2026-08-24T11:34:02Z

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gaaclarke · 2026-09-14T22:14:57Z

As for enabling unit tests, we'll probably want to add two configs similar to this one, but one on firefox and one on safari: https://github.com/flutter/flutter/blob/master/engine/src/flutter/lib/web_ui/test/felt_config.yaml#L150
Once you've added it to felt_config.yaml you can run felt generate-builder-json and it will modify the appropriate engine_v2 json file to add the test suites to our CI runs

@eyebrowsoffire I'm circling back to this. In 2b5ef64fc41 you mention "Firefox+ui doesn't work because our Linux bots have no GPU and therefore no WebGL2 support, so that one is disabled." You can see that in the diff too here.

It sounds like there is no existing CI setup that can run wimp on firefox? What are your expectations for this PR with respect to felt testing?

gaaclarke · 2026-09-16T23:27:07Z

@eyebrowsoffire okay, I've stubbed in the image decoding and added a felt test config.

The image decoding returns a static image for animated images on safari and returns an empty image on firefox. I didn't dig deep into why, but they don't crash as requested.

The tests don't all pass, this appears to be an existing bug we can address in future PRs.

The tests aren't tied to CI, this matches the behavior of existing comparable test suites. Hopefully we can get them running on CI in the future but that seems out of scope of this PR considering it wasn't tackled yet in other suites, like firefox-dart2wasm-skwasm-ui

eyebrowsoffire

This is looking good, but I think there's something slightly wrong with the boolean logic on the codec stuff.

# Conflicts: # engine/src/flutter/lib/web_ui/test/felt_config.yaml

eyebrowsoffire

LGTM!

issue: flutter#187212 This gets wimp_heavy loading on firefox. There are still some webgl errors though. ## video Before this change nothing rendered for counter, now it works as long as you don't hover over the floating button. https://github.com/user-attachments/assets/e68facbe-50a4-4d19-80a3-6967aba2691f ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. If this change needs to override an active code freeze, provide a comment explaining why. The code freeze workflow can be overridden by code reviewers. See pinned issues for any active code freezes with guidance. **Note**: The Flutter team is currently trialing the use of [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code). Comments from the `gemini-code-assist` bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

flutter-dashboard Bot added the CICD Run CI/CD label Jul 23, 2026

gaaclarke changed the title ~~Wimp heavy~~ [wimp] Adds wimp-heavy variant for non-chrome browsers Jul 23, 2026

gaaclarke requested review from eyebrowsoffire and walley892 July 23, 2026 21:34

gemini-code-assist Bot reviewed Jul 23, 2026

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github-actions Bot added engine flutter/engine related. See also e: labels. platform-web Web applications specifically team-web Owned by Web platform team labels Jul 23, 2026

gaaclarke mentioned this pull request Jul 23, 2026

[wimp] Support non-chrome browsers with wimp #187212

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eyebrowsoffire requested changes Jul 23, 2026

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gaaclarke requested a review from eyebrowsoffire July 23, 2026 22:50

gaaclarke force-pushed the wimp-heavy branch from 9dc8cf1 to 95fab22 Compare July 27, 2026 23:34

gaaclarke force-pushed the wimp-heavy branch 2 times, most recently from 4d7cf65 to d6bd418 Compare September 11, 2026 22:07

gaaclarke added 4 commits September 16, 2026 16:23

Adds wimp-heavy build

12425d8

stubbed in animated images

7aa76a7

adds felt configs

66c1238

stubbed 2

7e2f726

gaaclarke force-pushed the wimp-heavy branch from 8d28bc9 to 7e2f726 Compare September 16, 2026 23:23

added test

6ef5944

eyebrowsoffire requested changes Sep 17, 2026

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Comment thread engine/src/flutter/lib/web_ui/lib/src/engine/image_decoder.dart Resolved

Comment thread engine/src/flutter/lib/web_ui/lib/src/engine/image_decoder.dart Resolved

gaaclarke added 2 commits October 22, 2026 16:35

Merge remote-tracking branch 'origin/master' into wimp-heavy

6b5653d

# Conflicts: # engine/src/flutter/lib/web_ui/test/felt_config.yaml

jackson feedback

30c1782

gaaclarke requested a review from eyebrowsoffire October 22, 2026 23:58

eyebrowsoffire approved these changes Oct 23, 2026

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gaaclarke added the autosubmit Merge PR when tree becomes green via auto submit App label Oct 23, 2026

auto-submit Bot added this pull request to the merge queue Oct 23, 2026

Merged via the queue into flutter:master with commit 93197e2 Oct 23, 2026
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flutter-dashboard Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Oct 23, 2026

	? (config.enableWimp ? 'wimp_heavy' : 'skwasm_heavy')
	? (config?.enableWimp ? 'wimp_heavy' : 'skwasm_heavy')

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