Loïc Sharma f79695512e [Windows] Don't block raster thread until v-blank (flutter/engine#41231) ...

Currently the Windows raster thread blocks until the v-blank. As a result, on Windows a frame can spend 17ms on the raster thread even if rasterization completes in under 1ms. This behavior prevents us from rendering multiple views on the same raster thread on Windows.

This change does not make rasterization faster. Instead, it allows the raster thread to do more work. 

Addresses https://github.com/flutter/flutter/issues/124903

### Results

Here are the performance graphs if I hover on and off the counter app's button repeatedly.

#### Before 
The raster thread spends ~17ms per frame consistently:

![Pasted image 20230414180144](https://user-images.githubusercontent.com/737941/232175444-f4b8eb64-b8a3-47b3-aa85-112c56d596a2.png)

#### After
After this change, the raster thread spends less than 1ms per frame consistently:
![Pasted image 20230414180011](https://user-images.githubusercontent.com/737941/232176377-a2f26c41-dfd1-4140-a775-59d6f0fac31f.png)

### Background

Blocking until the v-blank prevents screen tearing if the OS does not synchronize to the vsync. Windows does synchronize if the Desktop Windows Manager composition is enabled, which is required on Windows 8 and newer. In other words, this blocking behavior is unnecessary for Windows 8 and newer.

For Windows 7, screen tearing is possible if DWM composition is disabled (either by the user or by an app). In this scenario, the Flutter app should block until the v-blank to synchronize with the vsync and prevent screen tearing. We can detect if DWM composition is disabled using [`DwmIsCompositionEnabled`](https://learn.microsoft.com/en-us/windows/win32/api/dwmapi/nf-dwmapi-dwmiscompositionenabled). We can detect changes to DWM composition using the top-level [`WM_DWMCOMPOSITIONCHANGED`](https://learn.microsoft.com/en-us/windows/win32/dwm/wm-dwmcompositionchanged) Windows message.

Useful resources:
1. https://learn.microsoft.com/en-us/windows/win32/dwm/composition-ovw
2. https://www.khronos.org/opengl/wiki/Swap_Interval
3. https://forums.imgtec.com/t/eglswapinterval-0-tearing-problem/2356/5
4. https://stackoverflow.com/questions/32282252/can-eglswapinterval0-cause-screen-tearing
5. https://bugs.chromium.org/p/chromium/issues/detail?id=480361

2023-04-21 01:01:50 +00:00

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src/flutter

[Windows] Don't block raster thread until v-blank (flutter/engine#41231)

2023-04-21 01:01:50 +00:00