[web] Raster Pictures at full screen size in Skwasm #174456

harryterkelsen · 2025-08-26T18:26:45Z

Skwams currently rasters images at their cullRect size, and resizes the bitmaprenderer canvas that will display the bitmap to the cullRect size. It is unclear if the speed-up from the smaller bitmap creation outweighs the cost of resizing and recreating the bitmaprenderer canvas.

To prepare for the web renderer unification and unify the rasterization step between the two renderers, this change makes it so Skwasm rasters the pictures at the full screen size, and no longer needs to resize the bitmaprenderer canvases unless the screen size changes.

Part of #172311

Pre-launch Checklist

I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is test-exempt.
I followed the breaking change policy and added Data Driven Fixes where supported.
All existing and new tests are passing.

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Code Review

This pull request modifies the Skwasm web renderer to rasterize pictures at the full screen size, instead of their individual cull rectangle sizes. This change is intended to unify the rasterization logic with other web renderers. The changes span across Dart, JavaScript, and C++ code, updating function signatures to pass screen dimensions down to the rasterizer. The underlying canvas resizing logic in C++ is updated to handle fixed-size screen canvases, and the JavaScript layer is optimized to use transferToImageBitmap for better performance. Additionally, a new test file is added to ensure culling logic remains correct.

engine/src/flutter/lib/web_ui/skwasm/surface.cpp

eyebrowsoffire

Looks good! I think there is some opportunity for cleanup though.

eyebrowsoffire · 2025-08-26T19:31:54Z

engine/src/flutter/lib/web_ui/lib/src/engine/scene_view.dart

 // composite pictures into the canvases in the DOM tree it builds.
 abstract class PictureRenderer {
-  FutureOr<RenderResult> renderPictures(List<ScenePicture> picture);
+  FutureOr<RenderResult> renderPictures(List<ScenePicture> picture, int width, int height);


I think with this change, you can remove the code paths that use the clipPicture stuff. Basically if the cullRect of any picture is beyond the bounds of the screen, we redraw the picture, clipping it to the screen. But since you're rendering this way where you are setting the width/height explicitly, I don't think any of that clipping stuff is necessary anymore.

eyebrowsoffire

LGTM!

auto-submit · 2025-08-26T22:32:27Z

autosubmit label was removed for flutter/flutter/174456, because - The status or check suite Linux linux_web_engine_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.

mdebbar · 2025-08-27T14:42:29Z

engine/src/flutter/lib/web_ui/lib/src/engine/scene_view.dart

    final List<LayerSlice?> slices = scene.rootLayer.slices;
    final List<ScenePicture> picturesToRender = <ScenePicture>[];
-    final List<ScenePicture> originalPicturesToRender = <ScenePicture>[];
    final List<ScenePicture> picturesToFree = <ScenePicture>[];


picturesToFree is not used anymore.

flutter-dashboard · 2025-08-27T18:21:16Z

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Changes reported for pull request #174456 at sha 20d1d01

…r/flutter#174456)

Skwams currently rasters images at their `cullRect` size, and resizes the `bitmaprenderer` canvas that will display the bitmap to the `cullRect` size. It is unclear if the speed-up from the smaller bitmap creation outweighs the cost of resizing and recreating the `bitmaprenderer` canvas. To prepare for the web renderer unification and unify the rasterization step between the two renderers, this change makes it so Skwasm rasters the pictures at the full screen size, and no longer needs to resize the `bitmaprenderer` canvases unless the screen size changes. Part of flutter#172311 ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [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]. **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 [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

…r/flutter#174456)

Skwams currently rasters images at their `cullRect` size, and resizes the `bitmaprenderer` canvas that will display the bitmap to the `cullRect` size. It is unclear if the speed-up from the smaller bitmap creation outweighs the cost of resizing and recreating the `bitmaprenderer` canvas. To prepare for the web renderer unification and unify the rasterization step between the two renderers, this change makes it so Skwasm rasters the pictures at the full screen size, and no longer needs to resize the `bitmaprenderer` canvases unless the screen size changes. Part of flutter#172311 ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [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]. **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 [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

harryterkelsen requested a review from eyebrowsoffire August 26, 2025 18:26

github-actions bot added engine flutter/engine related. See also e: labels. platform-web Web applications specifically labels Aug 26, 2025

harryterkelsen requested a review from mdebbar August 26, 2025 18:26

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harryterkelsen requested a review from eyebrowsoffire August 26, 2025 20:04

harryterkelsen added 7 commits August 26, 2025 14:07

Move SceneBuilder and Platform View code out of CanvasKit

167d923

Fix commits that are a result of bad merge

4097cd4

Trigger rebuild

538d414

Rasterize Skwasm images at full screen size

a5b78a9

Respond to comments

0cd33e1

rename _resize -> _resizeSurface

f6d06ff

Remove no-longer-needed clipPicture methods

60acfe1

harryterkelsen force-pushed the skwasm-render-full-screen branch from 70b898e to 60acfe1 Compare August 26, 2025 21:10

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harryterkelsen added the autosubmit Merge PR when tree becomes green via auto submit App label Aug 26, 2025

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Update scene_view tests

cb09d9a

mdebbar reviewed Aug 27, 2025

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Fix analysis warning. Remove unused code.

20d1d01

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Merged via the queue into flutter:master with commit 53a4cde Aug 27, 2025
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