wayland: add wp-fractional-scale-v1 support

[Dudemanguy]

Currently depends on wayland-protocols from master. Presumably they'll cut a new release soon though since this is a pretty major feature. Now depends on wayland-protocols 1.31.

Tested this on sway/wlroots with https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3511 and swaywm/sway#6929 (with the later rebased/cherry-picked locally). Seems to work as desired and fortunately it's not nearly as invasive into mpv's geometry handling as I initially feared.

This does sort of change the semantics of how mpv on wayland handles HiDPI but it's actually more inline with other platforms now. Basically, the window is always scaled by the extra scale factor. Previously, it was always shown as the exact pixel size with no extra scaling.

Eventually, I'd like to eliminate the old buffer_scale codepath and logic completely because the fractional scale protocol is simply better in every way, but that will have to wait for the future so for now we have to juggle these three different cases (fractional scale, regular wayland integer scaling, and no scaling at all).

TODO:

• Fix autofit/geometry options
• Actually tie this to a wayland-protocols release
• waf support
• Document the change in scaling behavior
• Support the --no-hidpi-window-scale option with the fractional scale method
• More testing in general

Fixes #9443.

[Dudemanguy]

Unfortunately, it's pretty trivial to trigger some "off-by-one" errors in the window dimensions in certain cases (playing around with current-window-scale) with this current approach. I think I might have to rework wl->geometry so it represents the physical not logical space.

[Dudemanguy]

I think I might have to rework wl->geometry so it represents the physical not logical space.

This seems to do the trick.

This now depends on wayland-protocols 1.31. Seems to behave OK in the fractional-scale support case while still working the same as before without it. I'll try to rig up multi monitors later to do some more testing.

[Dudemanguy]

This is going to be the greatest clusterfuck I've ever written.

Did some more testing with multimonitors on Plasma (built from an arbitrary git commit from master) as well as my rebased Sway/wlroots branch. Tweaked some things, and in general it seems to work. This is insanely complicated though (was already bad enough before), but there's really nothing I can do about it. There's so many different ways to scale now and I can't just drop the buffer_scale stuff. I pray that compositor devs can get fractional scale support quickly, so I can drop some code ASAP. btw the cursor isn't fractionally scaled (nobody better complain about this I swear).

I'm sure there's regressions, but anyways I'll think on it for a few more days before merging so people out there can actually use the thing (the next KDE release will drop soonish with this) and report breakage.

[Dudemanguy]

Okay, I don't think I hate this anymore after this third rewrite.

[davispuh]

Okay, I don't think I hate this anymore after this third rewrite.

Great job and well done! 🥳 and high five ✋ as I have basically just completed 3rd rewrite of some KDE Dolphin related stuff aswell 😅 just few bugs left to fix before submitting MR :)