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[Windows] Add callback for when the next frame is drawn #35408

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auto-submit merged 10 commits into from
Aug 15, 2022
Merged

[Windows] Add callback for when the next frame is drawn #35408

auto-submit merged 10 commits into from
Aug 15, 2022

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@loic-sharma loic-sharma commented Aug 15, 2022

Adds a Windows desktop API to be notified when the next frame has been drawn. In the future, this will be used by Windows app to hide the window until the first frame has been drawn. This effectively just exposes the corresponding API in embedder.h.

Follow up to: #35244

Part of flutter/flutter#41980

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loic-sharma
loic-sharma commented Aug 15, 2022
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shell/platform/windows/flutter_windows_unittests.cc
Comment on lines +186 to +191
// Pump messages for the Windows platform task runner.
::MSG msg;
while (::GetMessage(&msg, nullptr, 0, 0)) {
::TranslateMessage(&msg);
::DispatchMessage(&msg);
}
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@loic-sharma loic-sharma Aug 15, 2022 •
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This is necessary as otherwise platform tasks - including the next frame callback - won't run. The Windows platform thread's task runner is actually a window. It is woken up by posting a message to its window. If messages aren't dispatched, the Windows platform task runner is never woken up, and platform tasks are never executed.

yaakovschectman
yaakovschectman approved these changes Aug 15, 2022
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LGTM
It looks the existing next frame callback handling that these changes utilize work by passing the callback around through several layers of abstraction (e.g. engine, embedder, delegate) before eventually ending up at the Rasterizer, am I understanding that right?

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loic-sharma commented Aug 15, 2022 •
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@yaakovschectman Yup that's correct. The full chain will be:

  1. (TODO) App registers a first frame callback using the Windows desktop's next frame API
  2. Windows desktop API registers a next frame callback using the embedder's next frame API
  3. Embedder API registers a next frame callback using the shell
  4. The shell posts a task to the raster thread to set the rasterizer's next frame callback
  5. After the rasterizer draws the next frame, it fires its next frame callback if one exists from the raster thread
  6. This executes the embedder API's next frame callback
  7. This executes the Windows desktop API's next frame callback, which switches to the platform thread
  8. (TODO) This executes the app's first frame callback

cbracken
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LGTM stamp from a Japanese personal seal

@loic-sharma loic-sharma added the autosubmit Merge PR when tree becomes green via auto submit App label Aug 15, 2022
@auto-submit auto-submit bot merged commit a47ddf9 into flutter:main Aug 15, 2022
@loic-sharma loic-sharma deleted the windows_first_frame branch August 15, 2022 23:40
@engine-flutter-autoroll engine-flutter-autoroll mentioned this pull request Aug 16, 2022
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engine-flutter-autoroll added a commit to engine-flutter-autoroll/flutter that referenced this pull request Aug 16, 2022
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a47ddf9 [Windows] Add callback for when the next frame is drawn (flut…
35ac42a 
…ter/engine#35408)
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