High-resolution scroll wheel support

Merged José Expósito requested to merge JoseExposito/wlroots:hi-res-scrolling into master

The first revision of this MR was opened on GitHub. Since the project was migrated to GitLab I can not edit it anymore.

This is the second revision adding the changes suggested by Simon here: !3082 (closed)


Starting with Linux Kernel v5.0 two new axes are available for high-resolution wheel scrolling: REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES. Both axes send data in fractions of 120 where each multiple of 120 amounts to one logical scroll event. Fractions of 120 indicate a wheel movement less than one detent. A "detent" is the named used in the Kernel for a mouse wheel click: https://www.kernel.org/doc/html/v5.11-rc7/input/event-codes.html#ev-rel

Three new events are now available on libinput: LIBINPUT_EVENT_POINTER_SCROLL_WHEEL, LIBINPUT_EVENT_POINTER_SCROLL_FINGER, and LIBINPUT_EVENT_POINTER_SCROLL_CONTINUOUS. These events replace the LIBINPUT_EVENT_POINTER_AXIS event, so new clients should simply ignore that event.

This LIBINPUT_EVENT_POINTER_SCROLL_WHEEL event adds a new API libinput_pointer_scroll_get_value_v120(). The libinput_pointer_scroll_get_value_v120() is a mirror from the kernel API (itself a copy of the Windows API). The new event is sent for all wheel events, even those that don't technically support high-resolution scrolling and even on older kernels that don't have this feature. So callers can simply ignore any LIBINPUT_EVENT_POINTER_AXIS event and use the new event types only.

For LIBINPUT_EVENT_POINTER_SCROLL_FINGER and LIBINPUT_EVENT_POINTER_SCROLL_CONTINUOUS, as well as LIBINPUT_EVENT_POINTER_SCROLL_WHEEL, a new API is available: libinput_pointer_scroll_get_value(). This API is similar to libinput_pointer_axis_get_value().


How to test it:

Install libinput >= 1.19.

Clone and install Peter's Wayland protocol: wayland/wayland!72 (merged)


To test with a client that supports high-resolution scroll, clone my GTK branch: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/3839

And run it:

$ meson build --prefix=`pwd`/build/install --buildtype=debug # Installing here to not replace your stable GTK
$ ninja -C build && \
   ninja -C build install && \
   GDK_BACKEND=wayland WAYLAND_DEBUG=1 XDG_DATA_DIRS=`pwd`/build/install/share:$XDG_DATA_DIRS LD_LIBRARY_PATH=`pwd`/build/install/lib64:$LD_LIBRARY_PATH ./build/install/bin/gtk4-demo

Of course, you'll need hardware to test it. Logitech mice are supported, otherwise any mouse that shows a ResolutionMultiplier in the hid-recorder output (most Microsoft-branded mice of the last decade).

cc @emersion @whot

Fix #1627 (closed)

Edited by José Expósito

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