impeller: makes deferred display list images trash their display lists after they are realized by gaaclarke · Pull Request #178259 · flutter/flutter

gaaclarke · 2025-11-10T21:59:18Z

This stops ballooning recursive display_lists that can happen in animations. The display list actually can be larger than the image so keeping the display list around is no benefit. In rare cases this could make the memory size of backgrounded apps be larger but this keeps images made with toImageSync have the same semantics as toImage on impeller.

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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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Note: The Flutter team is currently trialing the use of Gemini Code Assist for GitHub. 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.

jason-simmons

One potential issue is that this may result in usages of toImageSync that are safe when using Impeller but consume excessive resources on platforms that are still using Skia. App developers will need to be aware of this as long as Skia remains in use.

@chinmaygarde

gaaclarke · 2025-11-11T23:51:38Z

One potential issue is that this may result in usages of toImageSync that are safe when using Impeller but consume excessive resources on platforms that are still using Skia. App developers will need to be aware of this as long as Skia remains in use.

I think that's fine because this isn't the only place this happens. Impeller was created with the intention to be a renderer with better performance for Flutter's use case. That means there are all sorts of usages that are supposed to be better on impeller than on skia. We don't want logical changes, but performance changes are expected.

jason-simmons · 2025-11-12T00:04:55Z

 }

 void DlDeferredImageGPUImpeller::ImageWrapper::SnapshotDisplayList(
+    sk_sp<DisplayList> display_list,


Declare this parameter as a std::variant to indicate that this takes either a DisplayList or a LayerTree but not both.

jason-simmons · 2025-11-12T00:10:21Z

@@ -106,7 +111,8 @@ class DlDeferredImageGPUImpeller final : public DlImage {
    // thread task spawned by this method. After being flattened into a display
    // list, the image wrapper will be updated to hold this display list and the


Delete the part of this comment saying that the image wrapper will hold the display list.

jason-simmons · 2025-11-12T00:11:22Z

+          display_list = layer_tree->Flatten(
              DlRect::MakeWH(wrapper->size_.width, wrapper->size_.height),
-              wrapper->texture_registry_);
+              texture_registry);


The texture_registry variable can be removed and snapshot_delegate->GetTextureRegistry() can be passed here

jason-simmons · 2025-11-12T00:31:59Z

+namespace testing {
+namespace {
+
+void PostTaskSync(const fml::RefPtr<fml::TaskRunner>& task_runner,


Remove the local version of this function and use the one from #include "flutter/testing/post_task_sync.h"

jason-simmons · 2025-11-12T01:04:50Z

    fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate,
    fml::RefPtr<fml::TaskRunner> raster_task_runner)
    : size_(size),
-      display_list_(std::move(display_list)),


Remove the display_list parameter from the ImageWrapper constructor

std::variant removed posttasksync inlined variable removed arg update comment

gaaclarke · 2025-11-12T17:40:08Z

+    void SnapshotDisplayList(
+        std::variant<sk_sp<DisplayList>, std::unique_ptr<LayerTree>> content);


Looking at this now, we probably should have just overloaded the constructor. Oh well, that was fun.

…lay lists after they are realized (flutter/flutter#178259)

…s after they are realized (flutter#178259) fixes flutter#138627 This stops ballooning recursive display_lists that can happen in animations. The display list actually can be larger than the image so keeping the display list around is no benefit. In rare cases this could make the memory size of backgrounded apps be larger but this keeps images made with toImageSync have the same semantics as toImage on impeller. ## 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

…lay lists after they are realized (flutter/flutter#178259)

gaaclarke added 7 commits November 7, 2025 17:52

Made deferred impeller images absorb their display lists

8720854

added test for trashing

4a14f04

posttasksync

9fc1fd6

added assert that pauses raster thread

9175ae7

cleanup

451005b

removed grcontext creation callbacks

0b8b2c8

format

5248c00

github-actions Bot added the engine flutter/engine related. See also e: labels. label Nov 10, 2025

gaaclarke added 3 commits November 10, 2025 14:35

moved out duplicated mock objects

bf45245

pulled out shared snapshotdelegate

eb6a4b2

pulled out dlimage

e86b7a8

github-actions Bot added the e: impeller Impeller rendering backend issues and features requests label Nov 10, 2025

gaaclarke changed the title ~~Deferred image realized~~ impeller: makes deferred display list images trash their display lists after they are realized Nov 10, 2025

gaaclarke added 2 commits November 10, 2025 15:11

revert workspace changes

ad858e0

tidy

0ec18c7

gaaclarke marked this pull request as ready for review November 10, 2025 23:46

gaaclarke requested a review from jason-simmons November 10, 2025 23:47

jason-simmons added fyit-ool and removed fyit-ool labels Nov 11, 2025

jason-simmons reviewed Nov 11, 2025

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Comment thread engine/src/flutter/lib/ui/painting/display_list_deferred_image_gpu_impeller.cc Outdated

Comment thread engine/src/flutter/lib/ui/painting/display_list_deferred_image_gpu_impeller.cc Outdated

jason feedback

5a671cf

gaaclarke requested a review from jason-simmons November 11, 2025 23:51

jason-simmons reviewed Nov 12, 2025

View reviewed changes

jason feedback

fe22d66

std::variant removed posttasksync inlined variable removed arg update comment

gaaclarke requested a review from jason-simmons November 12, 2025 17:38

gaaclarke commented Nov 12, 2025

View reviewed changes

jason-simmons approved these changes Nov 12, 2025

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gaaclarke added the autosubmit Merge PR when tree becomes green via auto submit App label Nov 12, 2025

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…lay lists after they are realized (flutter/flutter#178259)

		@@ -106,7 +111,8 @@ class DlDeferredImageGPUImpeller final : public DlImage {
		// thread task spawned by this method. After being flattened into a display
		// list, the image wrapper will be updated to hold this display list and the

		void SnapshotDisplayList(
		std::variant<sk_sp<DisplayList>, std::unique_ptr<LayerTree>> content);

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gaaclarke commented Nov 10, 2025 •

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