Touchpad gestures

[YaLTeR]

Implements zwp_pointer_gestures_v1 and the entire Smithay support for it.

The Wayland gesture objects store whether they are currently active (i.e. between begin() and end()) on a given WlSurface. When receiving gesture update or end event, this field is checked, and if it doesn't match, then the gesture is cancelled. This way, gesture objects bound mid-gesture, or something equally weird happening, won't receive update() with no begin().

You could do something smarter, e.g. mutter will synthesize a gesture begin event if you move the pointer onto a surface mid-gesture, but doing this sounds quite more complex (need to track ongoing gestures on the pointer), and I don't think this usecase is very realistic (for this to happen you have to do something along move the pointer with a mouse while also making a gesture on the touchpad).

Anyway, here's a demo on my compositor, but it works in Anvil too, even on Xwayland windows.

gestures.mp4

Here you can see the pinch zoom/rotate gesture visually in gtk4-demo, then the swipe gesture only in WAYLAND_DEBUG on the right, then the hold gesture by stopping the kinetic scrolling by putting a finger on the touchpad.

By default an Anvil build won't have the hold gestures, to enable them build with the smithay/libinput_1_19 feature.

[Drakulix]

Thanks for doing the work!

Lots and lots of plumbing code, but nothing problematic. I didn't even realize libinput just gave us gesture events (too long since I wrote the bindings...), so thanks for wiring that up!

I'll wait for a resolution on the name-conflict and possibly merge the clippy PR first so we get working CI, but otherwise this looks good for merge to me.

[YaLTeR]

Oh right, Smallvil.

[Drakulix]

Oh right, Smallvil.

I think it is fine to leave pointer gestures out of smallvil (cc @PolyMeilex).
So just stubs with comments should be enough to fix that.

[YaLTeR]

The winit backend does not generate gesture events, so yeah, it wouldn't work there anyway.

[YaLTeR]

Can't even default-impl those because of no lifetime bound on D

[YaLTeR]

Oh, and I forgot to write docs

[YaLTeR]

finally