Provide a vsync source

[Yoric]

Servo has an issue by which it attempts to repaint (and animate, etc.) 1500 times per second. For the moment, Glutin can behave as a vsync throttler by blocking until vsync, but discussing with Gecko gfx engineers, we concluded that the best way to solve this is to provide a vsync source, and use it to trigger repaints at a reasonable framerate, as was recently added in Gecko.

I suspect that the best way to add this vsync source would be Glutin itself.

Cc @pcwalton, @nical.

[tomaka]

What does that mean in practice? As far as I know only swapping buffers with OpenGL blocks until a vsync.

[Yoric]

This means sending a signal when the hardware sends a hardware vsync signal.

[tomaka]

I guess by "signal" you mean an event.

I can't find anything related to that on the web. All I can find is how to specify the swap interval, which changes the behavior of SwapBuffers.

[Yoric]

In the document I quoted above, I see that the hardware event can be watched using CVDisplayLinkRef on MacOS X, DwmGetCompositionTimingInfo on Windows, HwcComposer2D on Android. I don't see anything about other platforms.

[Yoric]

What's your judgement, @tomaka? Should this be part of Glutin, or an independent crate/lib?

[tomaka]

Looking at DwmGetCompositionTimingInfo, in my opinion a function to query the refresh rate of the window should be part of glutin but the system that sends events is out of scope of glutin.

[kchibisov]

See rust-windowing/winit#2412.