White flash on app startup on Windows 11 dark mode

gfxenjoyer commented 1 month ago

Xilem apps have a white flash on Windows even on dark mode. This does not happen on macOS. I suspect this has something to do with winit.

Hardware: OS: Windows 11 23H2 OS Build 22631.4169 CPU: Intel 12600k GPU: Nvidia RTX 3080 Driver 560.70

This also happens in Vello examples.

Reference Zulipchat

xilem_calc_white_flash_windows.webm

Edit: Calc build in video shown is a release build.

DJMcNab commented 1 month ago

Thanks for the report. I believe that there are a few things going on here:

Windows will set a fully white buffer as the window contents initially. I don't know where this behaviour is documented
Graphics initialisation is taking a while on your machine. This doesn't really make sense, because your GPU is quite powerful; the biggest issue should have been resolved in linebender/vello#575
We might not present "soon enough" after making the window visible - see https://github.com/linebender/xilem/blob/b54266d605b597d967e4b13dcf04d2e43ce43691/masonry/src/event_loop_runner.rs#L261, but GPU initialisation hasn't happened yet.

Ultimately, I can't afford the time to dig into this at the moment, but hopefully this gives you some good directions to look towards when investigating this. In particular, you should try and find some documentation expressing a correct startup sequence for an app on Windows, or else perform some experiments (such as only making the window visible immediately before we call present for the first time - I am slightly concerned that rendering wouldn't be scheduled in that case...)

gfxenjoyer commented 1 week ago

egui had the same issue and fixed it by setting the window invisible until first render. https://github.com/emilk/egui/pull/3631

DJMcNab commented 2 days ago

A pr which experiments with that would be welcome!

linebender / xilem

White flash on app startup on Windows 11 dark mode #590