Investigate the advantage of enabling SkSL warmup

[swift-kim]

What is shader compilation jank?

https://flutter.dev/docs/perf/rendering/shader

How to enable SkSL warm-up on Tizen?

1. Set the FlutterProjectArgs.persistent_cache_path value to either a system temp directory or the app cache directory before starting the engine. Alternatively, the cache directory can be set by implementing fml::paths::GetCachesDirectory() in fml/platform/linux/paths_linux.cc (not tested). Shaders will be stored to this directory on the first run of an app, and the cached shaders will be used on subsequent runs.

2. You can optionally bundle the shaders with a tpk (as a json file in res/flutter_assets) to accelerate the first run of the app on other devices: https://flutter.dev/docs/perf/rendering/shader#how-to-use-sksl-warmup

Pros and cons

• Reduced shader compilation janks (not confirmed on Tizen - how can we measure this accurately?)
• Increased app startup latency because cached/bundled shaders need to be precompiled
  • The last measurement result: Investigate why SkSL shaders cannot be collected on Tizen devices #55 (comment)
• Slightly larger app size due to bundled shaders

Read more

• https://medium.com/flutter/whats-new-in-flutter-2-2-fd00c65e2039#7ed0

[xuelian-bai]

as the result I shown, sksl warmup can reduce time in GrGLProgramBuilder::finalize(), then reduce DrawSnapshot time about 200ms, but this will result in more time before OnMakecurrent in the same thread, that's why you can't see any improvement, I will check why.

[swift-kim]

@xuelian-bai Thank you for sharing. I was just to correct what you mentioned about the "launch time" because the sksl warmup typically doesn't reduce the startup time but rather increases it. From the medium link that I provided in the above comment, you will see

To avoid jank, Flutter has provided the ability to cache shaders during a training run, which are then packaged and bundled with an app, and compiled before the first frame while the Flutter Engine is starting up.

App startup latency is longer because the bundled shaders need to be precompiled.

[swift-kim]

Currently the following message is logged out to the console when an app is run with the --verbose-system-logs option in debug mode.

E/ConsoleMessage( 4279): [WARNING:flutter/common/graphics/persistent_cache.cc(258)] Could not acquire the persistent cache directory. Caching of GPU resources on disk is disabled.
E/ConsoleMessage( 4279): [INFO:persistent_cache.cc(227)] No sksl asset found.
E/ConsoleMessage( 4279): [INFO:gpu_surface_gl.cc(79)] Found 0 SkSL shaders; precompiled 0

[xuelian-bai]

did you set the path FlutterProjectArgs.persistent_cache_path?

[swift-kim]

@xuelian-bai No. I know why the error is displayed. The above comment just states the current status.

[swift-kim]

This will not be necessary if flutter-tizen/embedder#15 is implemented. Let's focus on flutter-tizen/embedder#15.