[web] Unify ui.Shader between CanvasKit and Skwasm by harryterkelsen · Pull Request #191232 · flutter/flutter

harryterkelsen · 2026-08-17T22:38:29Z

Refactors ui.Shader (including Gradient and ImageShader) to share core business logic between CanvasKit and Skwasm through the EngineShader layer. Backend-specific implementations are intentionally kept minimal, with both backends now only implementing BackendShader to provide the final native calls.

Part of #175630.

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Code Review

This pull request refactors the web engine's shader architecture by introducing unified EngineShader classes and abstract backend interfaces (BackendShader, BackendGradient, etc.) to decouple the frontend API from specific renderer implementations (CanvasKit and Skwasm). Feedback on these changes highlights potential memory leaks in both CanvasKit and Skwasm fragment shader samplers due to undisposed child image shaders, a missing filterQuality parameter forwarding in EngineFragmentShader.setImageSampler, and the compilation-out of color stop validations in release mode due to being wrapped in assert statements.

gemini-code-assist · 2026-08-17T22:40:57Z

+    assert(() {
+      _validateColorStops(colors, colorStops);
+      return true;
+    }());


Redundant and Assert-Only Validation of Color Stops\n\nWrapping _validateColorStops in an assert means that this validation is completely compiled out in release mode.\n\nIn Flutter mobile, _validateColorStops is called unconditionally in Gradient factories to throw an ArgumentError if the inputs are invalid. Disabling this on the web in release mode causes a behavioral divergence between mobile and web, and could lead to silent failures or obscure native crashes in CanvasKit/Skia.\n\nPlease call _validateColorStops unconditionally.

_validateColorStops(colors, colorStops);

References

Check for potential regressions: Look for changes that might break existing functionality or introduce unexpected behavior in related areas. ^(link)

This is how the native engine does it, so it should be fine to do it here as well.

The native engine doesn't wrap this in an assert. See:

flutter/engine/src/flutter/lib/ui/painting.dart

Lines 5237 to 5242 in ff6ef7f

super._() {

_validateColorStops(colors, colorStops);

final Float32List colorsBuffer = _encodeWideColorList(colors);

final Float32List? colorStopsBuffer = colorStops == null

? null

: Float32List.fromList(colorStops);

Oops, you're right. I changed it.

Part of flutter#175630. Refactors `ui.Shader` (including `Gradient` and `ImageShader`) to share core business logic between CanvasKit and Skwasm through the `EngineShader` layer. Backend-specific implementations are intentionally kept minimal, with both backends now only implementing `BackendShader` to provide the final native calls.

flutter-dashboard · 2026-08-18T18:00:31Z

CI had a failure that stopped further tests from running. We need to investigate to determine the root cause.

SHA at time of execution: 342c9d6.

Possible causes:

Configuration Changes: The .ci.yaml file might have been modified between the creation of this pull request and the start of this test run. This can lead to ci yaml validation errors.
Infrastructure Issues: Problems with the CI environment itself (e.g., quota) could have caused the failure.

A blank commit, or merging to head, will be required to resume running CI for this PR.

Error Details:

FormatException: ERROR: Mac_ios ios_debug_workflow is a new builder added. it needs to be marked bringup: true
If ci.yaml wasn't changed, try `git fetch upstream && git merge upstream/master`

Stack trace:

#0      CiYaml._validate (package:cocoon_service/src/model/ci_yaml/ci_yaml.dart:395:7)
#1      new CiYaml (package:cocoon_service/src/model/ci_yaml/ci_yaml.dart:128:7)
#2      new CiYamlSet (package:cocoon_service/src/model/ci_yaml/ci_yaml.dart:48:23)
#3      CiYamlFetcher._getCiYaml (package:cocoon_service/src/service/scheduler/ci_yaml_fetcher.dart:124:12)
<asynchronous suspension>
#4      Scheduler.getPresubmitTargets (package:cocoon_service/src/service/scheduler.dart:1088:20)
<asynchronous suspension>
#5      Scheduler._getTestsForStage (package:cocoon_service/src/service/scheduler.dart:1404:14)
<asynchronous suspension>
#6      Scheduler._runCiTestingStage (package:cocoon_service/src/service/scheduler.dart:1445:30)
<asynchronous suspension>
#7      Scheduler.proceedToCiTestingStage (package:cocoon_service/src/service/scheduler.dart:1554:7)
<asynchronous suspension>
#8      Scheduler._closeSuccessfulEngineBuildStage (package:cocoon_service/src/service/scheduler.dart:1351:5)
<asynchronous suspension>
#9      Scheduler.processCheckRunCompleted (package:cocoon_service/src/service/scheduler.dart:1277:11)
<asynchronous suspension>
#10     PresubmitSubscription._processBuild (package:cocoon_service/src/request_handlers/presubmit_subscription.dart:226:7)
<asynchronous suspension>
#11     PresubmitSubscription.post (package:cocoon_service/src/request_handlers/presubmit_subscription.dart:119:5)
<asynchronous suspension>
#12     RequestHandler.service (package:cocoon_service/src/request_handling/request_handler.dart:42:20)
<asynchronous suspension>
#13     SubscriptionHandler.service (package:cocoon_service/src/request_handling/subscription_handler.dart:134:5)
<asynchronous suspension>
#14     createServer.<anonymous closure> (package:cocoon_service/server.dart:462:7)
<asynchronous suspension>
#15     main.<anonymous closure>.<anonymous closure> (file:///app/app_dart/bin/gae_server.dart:192:9)
<asynchronous suspension>

mdebbar · 2026-08-18T19:26:56Z

+    assert(() {
+      _validateColorStops(colors, colorStops);
+      return true;
+    }());


The native engine doesn't wrap this in an assert. See:

flutter/engine/src/flutter/lib/ui/painting.dart

Lines 5237 to 5242 in ff6ef7f

super._() {

_validateColorStops(colors, colorStops);

final Float32List colorsBuffer = _encodeWideColorList(colors);

final Float32List? colorStopsBuffer = colorStops == null

? null

: Float32List.fromList(colorStops);

harryterkelsen · 2026-08-18T20:55:14Z

Thanks @mdebbar, PTAL!

mdebbar

auto-submit · 2026-08-18T22:09:32Z

autosubmit label was removed for flutter/flutter/191232, because - The status or check suite Dashboard Checks has failed. Please fix the issues identified (or deflake) before re-applying this label.

flutter-dashboard Bot added the CICD Run CI/CD label Aug 17, 2026

gemini-code-assist Bot reviewed Aug 17, 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 Aug 17, 2026

harryterkelsen force-pushed the unify-shader branch from 27766e4 to 92564fc Compare August 17, 2026 23:00

harryterkelsen force-pushed the unify-shader branch from 92564fc to 342c9d6 Compare August 18, 2026 17:13

Merge branch 'master' into unify-shader

0dc04d4

harryterkelsen requested a review from mdebbar August 18, 2026 19:12

mdebbar reviewed Aug 18, 2026

View reviewed changes

[web] Address review comments on Shader unification

6e499ad

mdebbar approved these changes Aug 18, 2026

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harryterkelsen added the autosubmit Merge PR when tree becomes green via auto submit App label Aug 18, 2026

auto-submit Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Aug 18, 2026

harryterkelsen added the autosubmit Merge PR when tree becomes green via auto submit App label Aug 19, 2026

auto-submit Bot added this pull request to the merge queue Aug 19, 2026

Merged via the queue into flutter:master with commit 74b8f23 Aug 19, 2026
28 checks passed

flutter-dashboard Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Aug 19, 2026

	super._() {
	_validateColorStops(colors, colorStops);
	final Float32List colorsBuffer = _encodeWideColorList(colors);
	final Float32List? colorStopsBuffer = colorStops == null
	? null
	: Float32List.fromList(colorStops);

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harryterkelsen commented Aug 17, 2026

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