MonitorHandle::scale_factor does not use fractional factor on Wayland

[dhardy]

I see MonitorHandle::scale_factor reporting 2 while Window::scale_factor correctly reports 1.5 on Wayland.

The docs of Window::scale_factor note that it uses wp-fractional-scale protocol if available, otherwise returning an integer factor. The docs of MonitorHandle::scale_factor do not mention any such limitation — is this just a doc issue?

BTW the apple_2 link is broken.

[kchibisov]

The monitor scale and window scale has nothing to do with each other on Wayland.

[dhardy]

Different protocol, sure, but is it a bug that MonitorHandle::scale_factor is not returning the (correct) fractional scale factor (as configured in kwin) or is it just a doc issue (protocol does not support reporting the correct scale here)?

It's a nuisance that I'm not getting the correct scale factor since I'm attempting to limit the window size to the screen size (also not really possible on multi-screen systems).

[kchibisov]

I mean, they are just separate, use the scale factor from the window not from the monitor, winit can't by any means return a fractional scaling from the monitor, because wayland doesn't have such information, at all.

The GTK folks had the same issue since they used heuristics, they were told to not do that anymore, because it's just plain wrong, since you don't know on which monitor you'll open anyway.

I can update docs explicitly saying that the scale factor is for the monitor, but window could have different scaling factor. There're compositor which set a scaling on per window basis, so you can have clients with 2, 1.5, 1 scaling on the same output at the same time without anything being blurry (KWIN does this as well, for XWayland only though).

[dhardy]

Sure, I have to use a different approach for sizing. But...

I can update docs explicitly saying that the scale factor is for the monitor

This is not true in my case: the reported value is 2 while the desktop has it set to 1.5. Possibly this means that MonitorHandle::scale_factor should never be used for any purpose.

[kchibisov]

This is not true in my case: the reported value is 2 while the desktop has it set to 1.5. Possibly this means that MonitorHandle::scale_factor should never be used for any purpose.

Exactly, that's what wayland devs will tell you as well, that's all just metadata about the outputs, nothing more.