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Defer TLHC PlatformViewWrapper frame post and avoid initial 1x1 buffer resize - #195861
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…r resize In Texture Layer Hybrid Composition (TLHC), `PlatformViewWrapper.draw(Canvas)` locks a hardware canvas from the offscreen `PlatformViewRenderTarget` surface, draws the embedded Android `View` hierarchy into its display list (`super.draw`), and previously called `surface.unlockCanvasAndPost(canvas)` synchronously inside `ViewRootImpl.performTraversals()`. On Android's `HardwareRenderer`, `Surface.unlockCanvasAndPost()` invokes `nSyncAndDrawFrame()` on the shared singleton `RenderThread` to rasterize and queue the `PlatformView`'s buffer. In observed traces on 120 Hz displays with complex `PlatformView`s such as `WebView`, calling `unlockCanvasAndPost()` inline during `performTraversals()` queues the platform view's `RenderThread` submission ahead of the Activity window's own `ThreadedRenderer.draw()` -> `nSyncAndDrawFrame()`, stalling the Activity's UI thread during traversal. Additionally, `PlatformViewsController.configureForTextureLayerComposition()` previously constructed `new PlatformViewWrapper(context, renderTarget)` before calling `renderTarget.resize(physicalWidth, physicalHeight)`. When `PlatformViewWrapper`'s constructor cleared the initial surface, `getSurface()` lazily allocated a fallback `1x1` `ImageReader` and locked/posted a `1x1` hardware canvas, only for `resizeRenderTarget()` to immediately close and recreate the `ImageReader` at the real physical size. This commit: 1. Records the child view hierarchy synchronously into `pendingFrameCanvas` during `PlatformViewWrapper.draw()`, and defers `pendingFrameSurface.unlockCanvasAndPost` + `renderTarget.scheduleFrame()` via `mainHandler.postAtFrontOfQueue(...)` so submission runs immediately after the current traversal's window sync completes rather than blocking inline during traversal. 2. Flushes any pending recorded frame synchronously before re-entering `draw()`, before `resizeRenderTarget()`, when window visibility leaves `VISIBLE` (`onWindowVisibilityChanged`), and before `release()` (skipping `renderTarget.scheduleFrame()` when releasing). 3. Calls `renderTarget.resize(physicalWidth, physicalHeight)` before constructing `PlatformViewWrapper` in `configureForTextureLayerComposition()`, avoiding the throwaway `1x1` buffer allocation and removing the redundant `viewWrapper.resizeRenderTarget()` call.
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This pull request modifies PlatformViewWrapper to defer posting recorded frames to the render target by scheduling the unlock and post operations on the main thread queue instead of executing them synchronously during the draw traversal. It introduces tracking for pending frames and flushes them during resize, release, and window visibility changes. Additionally, PlatformViewsController is updated to resize the render target prior to wrapper initialization, and comprehensive unit tests are added to verify these behaviors. I have no feedback to provide.
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LGTM. Before and after sequence diagrams might help more than the descriptions of the code in the PR description - just a thought.
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Yeah I could have explained this better. Android splits rendering into two phases (docs):
Both the app window and our offscreen platform view
Previously, we called With this change, Gemini made this mermaid diagram which I can't get to display right inside of github, so here's a picture, but it accurately captures my understanding: 
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Roll Flutter from 3623d2d34543 to 09175cdeac89 (61 revisions) flutter/flutter@3623d2d...09175cd 2026-11-06 [email protected] Roll Skia from ae35b7b2221f to 793b8ac73d4b (3 revisions) (flutter/flutter#196091) 2026-11-06 [email protected] [web] Rasterize scenes at the size passed to `FlutterView.render` (flutter/flutter#196052) 2026-11-06 [email protected] Roll Skia from 4aa043a81e0c to ae35b7b2221f (1 revision) (flutter/flutter#196086) 2026-11-06 [email protected] Roll Fuchsia Linux SDK from Fqe3UlLwAohsPbsCS... to KIc0XZbhLmvDpTluZ... (flutter/flutter#196085) 2026-11-06 [email protected] Allow a zero scale change in InteractiveViewer (flutter/flutter#194949) 2026-11-06 [email protected] Roll Skia from dd5c2553a856 to 4aa043a81e0c (2 revisions) (flutter/flutter#196079) 2026-11-06 [email protected] [web] Keep ImageFilter.blur bounds in equality and description (flutter/flutter#196013) 2026-11-06 [email protected] iOS: Remove unused PlatformViewIOS setup from FlutterPlatformViewsTest (flutter/flutter#196033) 2026-11-06 [email protected] Serialize LoggerTests that mutate the shared Logger (flutter/flutter#196028) 2026-11-06 [email protected] Use reverseDuration for the AnimatedCrossFade size animation (flutter/flutter#194860) 2026-11-05 [email protected] Roll Skia from a5aacd103e68 to dd5c2553a856 (8 revisions) (flutter/flutter#196073) 2026-11-05 [email protected] Fix ListWheelScrollView null check error when it reads itemIndex before content dimensions are set (flutter/flutter#194859) 2026-11-05 [email protected] Allow zero cross axis extent in SliverGridDelegateWithMaxCrossAxisExtent (flutter/flutter#194858) 2026-11-05 [email protected] Revert: Allow color delta tolerance in in-memory fuzzy image comparator (flutter/flutter#196067) 2026-11-05 [email protected] Revert: Mitigate snapshot race in 3D transform test by reducing loop density (flutter/flutter#196066) 2026-11-05 [email protected] Delegate createStream in ResizeImage and ScrollAwareImageProvider (flutter/flutter#194756) 2026-11-05 [email protected] [iOS] Introduce FlutterShell and move thread host and profiler (flutter/flutter#195388) 2026-11-05 [email protected] [web] Support FragmentShader.getImageSampler on CanvasKit and Skwasm (flutter/flutter#195854) 2026-11-05 [email protected] Deprecates setFloat API (flutter/flutter#195505) 2026-11-05 [email protected] [flutter_tools] Remove public GlobalToolContext and globals from runner (flutter/flutter#195561) 2026-11-05 [email protected] Defer TLHC PlatformViewWrapper frame post and avoid initial 1x1 buffer resize (flutter/flutter#195861) 2026-11-05 [email protected] Roll Skia from b5abed66da86 to a5aacd103e68 (17 revisions) (flutter/flutter#196054) 2026-11-05 [email protected] Made `FlutterWindowControllerSizeTest.SizedToContentNotResizable` more robust (flutter/flutter#195845) 2026-11-05 [email protected] Update docs for contributor ladder (flutter/flutter#196011) 2026-11-05 [email protected] [Impeller] Use the transfer stage for the Vulkan readback barrier (flutter/flutter#194991) 2026-11-05 [email protected] Remove Mac mac_unopt builder (flutter/flutter#196027) 2026-11-05 [email protected] Updated Instructions for Determining Gradle Version for `gradle_dists` in CIPD (flutter/flutter#193310) 2026-11-05 [email protected] Move ios_app_with_extensions_test into the tool integration shard (flutter/flutter#195609) 2026-11-05 [email protected] [web] Respect Uint8List view bounds when detecting animated WebP/GIF (flutter/flutter#196010) 2026-11-05 [email protected] Add platform_views_layout to build_tests so iOS/Android build breaks are caught in presubmit (flutter/flutter#192985) 2026-11-05 [email protected] [flutter_tools] Detect macOS TCC permission crashes and provide diagnostic guidance (flutter/flutter#192432) 2026-11-05 [email protected] Roll Packages from 670b30e to 0478162 (15 revisions) (flutter/flutter#196047) 2026-11-05 [email protected] [web] Support Skwasm rendering without bitmap capture (flutter/flutter#195103) 2026-11-05 [email protected] [flutter_tools] Reland fix for local CanvasKit asset paths on Windows (flutter/flutter#195770) 2026-11-05 [email protected] Roll Skia from f96be51af95d to b5abed66da86 (14 revisions) (flutter/flutter#196017) 2026-11-05 [email protected] Split chrome web engine test drone (flutter/flutter#195873) 2026-11-05 [email protected] Roll Dart SDK from c9153304136a to 6623b84628f3 (1 revision) (flutter/flutter#196026) 2026-11-05 [email protected] Roll ICU from 4fe960221710 to a0ea93436c52 (6 revisions) (flutter/flutter#196025) 2026-11-05 [email protected] Add more guidance in README and AGENTS for contributing to flutter_tools (flutter/flutter#195998) 2026-11-05 [email protected] Roll Fuchsia Linux SDK from p0HDXLISPIElJfSz7... to Fqe3UlLwAohsPbsCS... (flutter/flutter#196019) 2026-11-05 [email protected] Roll Dart SDK from e362a23e9738 to c9153304136a (18 revisions) (flutter/flutter#196014) 2026-11-05 [email protected] [Impeller] Fix dilation input bounds when clipping saveLayers (flutter/flutter#195652) 2026-11-05 [email protected] Add `variantOf` to the M3E migration checklist (flutter/flutter#195099) 2026-11-05 [email protected] [flutter_tools] Eliminate globals from remaining subsystem files (flutter/flutter#195555) 2026-11-05 [email protected] Fix gap flipping when dragging variable height reorderable items (flutter/flutter#194478) 2026-11-05 [email protected] [A11y] Send un-merged SemanticsNodes in the same update that first references them (flutter/flutter#195829) ...
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With this change, scrolling a TLHC platform view (e.g. a
WebView) goes from ~70 fps to 120 fps on my Pixel 9.Previously in TLHC,
PlatformViewWrapper.draw()locked a hardware canvas from thePlatformViewRenderTargetsurface, drew the child AndroidViewhierarchy into it, and calledsurface.unlockCanvasAndPost(canvas)synchronously insideViewRootImpl.performTraversals(). BecauseSurface.unlockCanvasAndPost()callsnSyncAndDrawFrame()on Android's sharedRenderThread, calling it inline duringperformTraversals()queued the platform view'sRenderThreadframe submission ahead of the Activity window's ownThreadedRendererframe sync, stalling the UI thread during traversal.Additionally, when creating a TLHC platform view,
PlatformViewsController.configureForTextureLayerComposition()previously constructedPlatformViewWrapper(which immediately locks and clears the render target's surface at its default1x1size) before resizing the render target to the platform view's actual dimensions, causing an unnecessary1x1ImageReaderallocation that was immediately discarded and recreated.This PR fixes both issues by:
pendingFrameCanvasduringPlatformViewWrapper.draw(), and deferringunlockCanvasAndPost()+renderTarget.scheduleFrame()viamainHandler.postAtFrontOfQueue(...)so it runs immediately after the current traversal's window sync finishes rather than stalling inline during traversal.draw()is re-entered in the same traversal, beforeresizeRenderTarget(), when window visibility leavesVISIBLE, and beforerelease()(without scheduling a redundant engine frame on release).PlatformViewRenderTargetto(physicalWidth, physicalHeight)before constructingPlatformViewWrapperinconfigureForTextureLayerComposition(), and removing the redundantviewWrapper.resizeRenderTarget()call afterward.