On MacOS Vsync does nothing (rendering occurs as fast as possible) if window is hidden

[kettle11]

This is easily tested by measuring time between frames, creating a window, and moving the window behind another window.

The frame time will drop to around 0. This effectively busy-loops and can quickly heat up a laptop or drain battery. I encountered a version of this issue (with a library similar to glutin) where I left a program running with my laptop closed and came back and it was super hot.

This is an issue other similar libraries have encountered as well:
libsdl-org/SDL#1871

Their solution was to insert a sleep when the window is not visible.

I put together a small repository that reproduces this issue: https://github.com/kettle11/winit_framerate_test

[kchibisov]

The same would be on X11 as well. Given that you can contol vsync at runtime without any issue I don't think it matters now.