[Impeller][Windows] Significantly slower startup compared to Skia

[EgorKoschel]

Steps to reproduce

Steps to reproduce

1. Use Flutter 3.47.1 stable
2. Clone the minimal reproduction project: https://github.com/EgorKoschel/flutter_impeller_windows_test
3. Run the application in release mode with the default Impeller renderer:
   flutter run -d windows --release
4. Observe the startup timing output.
5. In windows/runner/main.cpp, uncomment the following line to disable Impeller and use Skia:
   project.set_impeller_switch(flutter::ImpellerSwitch::Disabled);
6. Run exactly the same command again:
   flutter run -d windows --release
7. Compare the startup timings.

The project is a minimal Windows-only Flutter application without third-party dependencies or application-specific initialization.

With Impeller enabled, almost all of the additional startup time is spent while constructing flutter::FlutterViewController, before plugin registration.

Impeller

[STARTUP] DartProject created: 1 ms
[STARTUP] Win32Window OnCreate completed: 3 ms
[STARTUP] Before FlutterViewController: 3 ms
[IMPORTANT:flutter/shell/platform/embedder/embedder_surface_gl_impeller.cc(126)] Using the Impeller rendering backend (OpenGLESSDF).
[STARTUP] FlutterViewController created: 1186 ms
[STARTUP] Plugins registered: 1186 ms
[STARTUP] Flutter view attached: 1190 ms
[STARTUP] Window/Create completed: 1190 ms
[STARTUP] First Flutter frame: 1232 ms

Skia

[STARTUP] DartProject created: 1 ms
[STARTUP] Win32Window OnCreate completed: 4 ms
[STARTUP] Before FlutterViewController: 4 ms
[STARTUP] FlutterViewController created: 58 ms
[STARTUP] Plugins registered: 58 ms
[STARTUP] Flutter view attached: 69 ms
[STARTUP] Window/Create completed: 69 ms
[STARTUP] First Flutter frame: 165 ms

The FlutterViewController constructor therefore takes approximately:

• Impeller: 1183 ms
• Skia: 54 ms

The time to the first Flutter frame is approximately:

• Impeller: 1232 ms
• Skia: 165 ms

I repeated the test multiple times with both renderers. The results were consistent across repeated launches: Impeller consistently spent roughly 1 second or more constructing FlutterViewController, while Skia completed the same step in only a few dozen milliseconds. The large difference was reproducible and was not limited to the first launch.

Main channel

The issue is also reproducible on the current Flutter main channel, although the performance characteristics are different from Flutter 3.47.1 stable.

Impeller

[STARTUP] DartProject created: 1 ms
[STARTUP] Win32Window OnCreate completed: 3 ms
[STARTUP] Before FlutterViewController: 3 ms
[IMPORTANT:flutter/shell/platform/embedder/embedder_surface_gl_impeller.cc(127)] Using the Impeller rendering backend (OpenGLESSDF).
[STARTUP] FlutterViewController created: 101 ms
[STARTUP] Plugins registered: 101 ms
[STARTUP] Flutter view attached: 113 ms
[STARTUP] Window/Create completed: 113 ms
[STARTUP] First Flutter frame: 618 ms

Skia

[STARTUP] DartProject created: 1 ms
[STARTUP] Win32Window OnCreate completed: 3 ms
[STARTUP] Before FlutterViewController: 3 ms
[STARTUP] FlutterViewController created: 47 ms
[STARTUP] Plugins registered: 47 ms
[STARTUP] Flutter view attached: 55 ms
[STARTUP] Window/Create completed: 55 ms
[STARTUP] First Flutter frame: 134 ms

On the main channel, FlutterViewController creation is significantly faster than on Flutter 3.47.1 stable. However, startup with Impeller is still substantially slower overall.

Time to first Flutter frame:

• Impeller: 618 ms
• Skia: 134 ms

Impeller therefore takes approximately 4.6x longer to reach the first Flutter frame in this run.

On Flutter 3.47.1 stable, most of the delay occurs while constructing FlutterViewController. On the current main channel, that part has improved substantially, but a significant startup delay remains after FlutterViewController has been created and before the first Flutter frame is rendered.

Code sample

Minimal reproduction:

https://github.com/EgorKoschel/flutter_impeller_windows_test

The relevant timing instrumentation is placed immediately around the FlutterViewController constructor:

  PrintStartupTime("Before FlutterViewController");

  flutter_controller_ = std::make_unique<flutter::FlutterViewController>(
      frame.right - frame.left,
      frame.bottom - frame.top,
      project_);

  PrintStartupTime("FlutterViewController created");

Impeller is enabled by default.

For comparison with Skia, the reproduction project contains the following commented-out line in windows/runner/main.cpp:

flutter::DartProject project(L"data");

// Uncomment to disable Impeller and use Skia.
// project.set_impeller_switch(flutter::ImpellerSwitch::Disabled);

No other code is changed between the Impeller and Skia measurements.

Performance profiling on master channel

• The issue still persists on the master channel

Timeline Traces

The observed delay occurs during native Windows engine initialization, inside the flutter::FlutterViewController constructor and before plugin registration or the first Flutter frame.

The C++ timing instrumentation in the reproduction project was used to isolate this native startup delay.

Video demonstration

What target platforms are you seeing this bug on?

Windows

OS/Browser name and version | Device information

Windows 11 Pro 25H2, x64
OS build: 26200

GPU: Intel(R) UHD Graphics 770
GPU driver version: 32.0.101.7088
GPU driver date: 2026-06-17

Does the problem occur on emulator/simulator as well as on physical devices?

Unknown

Is the problem only reproducible with Impeller?

Yes

Logs

Flutter Doctor output

[√] Flutter (Channel stable, 3.47.1, on Microsoft Windows [Version 10.0.26200.9168], locale de-DE) [233ms]
• Flutter version 3.47.1 on channel stable at C:\src\flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 6655482 (8 days ago), 2026-08-19 10:07:23 -0700
• Engine revision 5d53178
• Dart version 3.13.1
• DevTools version 2.60.0
• Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations, enable-native-assets, enable-record-use, enable-swift-package-manager, omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration

[√] Windows Version (11 Pro 64-bit, 25H2, 2009) [1.253ms]

[√] Android toolchain - develop for Android devices (Android SDK version 36.0.0) [1.466ms]
• Android SDK at C:\Users\EgorKoschel\AppData\Local\Android\sdk
• Emulator version 35.4.9.0 (build_id 13025442) (CL:N/A)
• Platform android-36, build-tools 36.0.0
• Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
This is the JDK bundled with the latest Android Studio installation on this machine.
To manually set the JDK path, use: flutter config --jdk-dir="path/to/jdk".
• Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-9586694)
• All Android licenses accepted.

[√] Chrome - develop for the web [60ms]
• Chrome at C:\Users\EgorKoschel\AppData\Local\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.6.5) [59ms]
• Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
• Visual Studio Community 2022 version 17.6.33829.357
• Windows 10 SDK version 10.0.22000.0

[√] Connected device (3 available) [139ms]
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [Version 10.0.26200.9168]
• Chrome (web) • chrome • web-javascript • Google Chrome 151.0.7922.174
• Edge (web) • edge • web-javascript • Microsoft Edge 151.0.4129.107

[√] Network resources [362ms]
• All expected network resources are available.

• No issues found!

[puneetkukreja98]

@EgorKoschel Thanks for reporting this, routing this to team-engine for further investigation.
Findings:
Impeller:

Launching lib\main.dart on Windows in release mode...
Building Windows application...                                    68.7s
√ Built build\windows\x64\runner\Release\flutter_impeller_windows_test.exe

Flutter run key commands.
h List all available interactive commands.
c Clear the screen
q Quit (terminate the application on the device).

[STARTUP] DartProject created: 3 ms
[STARTUP] Win32Window OnCreate completed: 8 ms
[STARTUP] Before FlutterViewController: 8 ms
[IMPORTANT:flutter/shell/platform/embedder/embedder_surface_gl_impeller.cc(126)] Using the Impeller rendering backend (OpenGLESSDF).
[STARTUP] FlutterViewController created: 2168 ms
[STARTUP] Plugins registered: 2168 ms
[STARTUP] Flutter view attached: 2213 ms
[STARTUP] Window/Create completed: 2213 ms
[STARTUP] First Flutter frame: 2317 ms

Application finished.
PS C:\Google\flutter_impeller_windows_test> 

Impeller-disabled:

Launching lib\main.dart on Windows in release mode...
Building Windows application...                                    13.9s
√ Built build\windows\x64\runner\Release\flutter_impeller_windows_test.exe

Flutter run key commands.
h List all available interactive commands.
c Clear the screen
q Quit (terminate the application on the device).

[STARTUP] DartProject created: 3 ms
[STARTUP] Win32Window OnCreate completed: 8 ms
[STARTUP] Before FlutterViewController: 8 ms
[STARTUP] FlutterViewController created: 129 ms
[STARTUP] Plugins registered: 130 ms
[STARTUP] Flutter view attached: 156 ms
[STARTUP] Window/Create completed: 156 ms
[STARTUP] First Flutter frame: 323 ms

Application finished.
PS C:\Google\flutter_impeller_windows_test> 

Flutter doctor -v:

[√] Flutter (Channel stable, 3.47.1, on Microsoft Windows [Version 10.0.26200.9168], locale en-IN) [571ms]
    • Flutter version 3.47.1 on channel stable at C:\Developer\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 6655482ec0 (8 days ago), 2026-08-19 10:07:23 -0700
    • Engine revision 5d53178869
    • Dart version 3.13.1
    • DevTools version 2.60.0
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android,
      enable-ios, cli-animations, enable-native-assets, enable-record-use, enable-swift-package-manager,
      omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration

[√] Windows Version (Windows 11 or higher, 25H2, 2009) [3.1s]

[√] Android toolchain - develop for Android devices (Android SDK version 37.0.0) [6.0s]
    • Android SDK at C:\Users\Puneet\AppData\Local\Android\sdk
    • Emulator version 36.6.11.0 (build_id 15507667) (CL:N/A)
    • Platform android-37.1, build-tools 37.0.0
    • Java binary at: C:\Program Files\Android\Android Studio1\jbr\bin\java
      This is the JDK bundled with the latest Android Studio installation on this machine.
      To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment (build 21.0.10+-14961533-b1163.108)
    • All Android licenses accepted.

[√] Chrome - develop for the web [204ms]
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2026 18.3.2) [203ms]
    • Visual Studio at C:\Program Files\Microsoft Visual Studio\18\Community
    • Visual Studio Community 2026 version 18.3.11520.95
    • Windows 10 SDK version 10.0.26100.0

[√] Connected device (3 available) [486ms]
    • Windows (desktop) • windows • windows-x64    • Microsoft Windows [Version 10.0.26200.9168]
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 151.0.7922.172
    • Edge (web)        • edge    • web-javascript • Microsoft Edge 151.0.4129.107

[√] Network resources [1,184ms]
    • All expected network resources are available.

• No issues found!

[krll-kov]

Same for me

[SugarFatFree]

Confirming this on a different machine, with a real application rather than a minimal repro: MarkText Plus, a Flutter desktop Markdown editor (window_manager, file_picker, printing, etc.).

Time from process start to first frame, from the app's own startup trace, Windows release builds:

Flutter	Renderer	Startup
3.44.9	Skia (Impeller not available)	284–306 ms
3.47.2	Impeller (default)	2130–3330 ms
3.47.2	Skia (set_impeller_switch(ImpellerSwitch::Disabled))	291–634 ms

Two things this adds to the thread:

The 3.44.9 baseline. Same machine, same app, a version predating Impeller-by-default on Windows. It lands on the same numbers as 3.47.2-with-Skia, which rules out a general 3.47 startup regression — the cost tracks the renderer, not the version.

A trap for anyone else trying to A/B this. My first attempt switched renderers with the FLUTTER_ENGINE_SWITCHES / FLUTTER_ENGINE_SWITCH_n environment variables. In a release build those are ignored: GetSwitchesFromEnvironment is compiled out behind #ifndef FLUTTER_RELEASE, so both arms of the experiment run Impeller and the measured difference is noise. I concluded from that run that Impeller was not the cause, and was wrong. project.set_impeller_switch(...) — as used in the report above — is the only thing that works in a release build, and it reproduces the difference immediately.

The machine is a virtualised GPU on a corporate Windows host, which likely explains why the absolute numbers here are worse than the 1232 ms / 165 ms in the original report while the ratio is comparable.

[gaaclarke]

A certain amount of this is expected because we are compiling shaders at launch to avoid jank while the app is running. The opengles backend doesn't let us precompile shaders like we can for metal and vulkan. Still this is a really high number that we can try to investigate. Ultimately we might have to just rely on a vulkan/dx12 backend though.