plugins: add a plugin to emulate high-resolution wheel events

Fixes a regression causing missing scroll events on devices where the
kernel only sets REL_WHEEL/REL_HWHEEL but not the corresponding
hires events. On those devices we would get the legacy axis events but
no longer the new ones.

The mouse wheel plugin will correctly emulate missing hires events
but it doesn't attach to devices where the hires bit is never set.

This plugin can be very simple - since we know we enabled the code on
this device we don't need to keep any extra state around. If our frame
handler is called for this device we want to add the hi-res events.

Theoretically this breaks if the device has only one hi-res axis enabled
but not the other one (i.e. REL_WHEEL_HI_RES but only REL_HWHEEL) but
that's too theoretical to worry about.

Closes #1156

Fixes: 31854a829a ("plugin: only register the wheel plugin on devices that have a wheel")
Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1268>

meson.build

@@ -384,6 +384,7 @@ src_libinput = src_libfilter + [
 	'src/libinput-plugin.c',
 	'src/libinput-plugin-button-debounce.c',
 	'src/libinput-plugin-mouse-wheel.c',
+	'src/libinput-plugin-mouse-wheel-lowres.c',
 	'src/libinput-plugin-tablet-double-tool.c',
 	'src/libinput-plugin-tablet-eraser-button.c',
 	'src/libinput-plugin-tablet-forced-tool.c',

src/libinput-plugin-mouse-wheel-lowres.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright © 2025 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <libevdev/libevdev.h>
+
+#include "evdev.h"
+#include "libinput-plugin-mouse-wheel-lowres.h"
+#include "libinput-plugin.h"
+#include "src/evdev-frame.h"
+
+static void
+wheel_plugin_device_new(struct libinput_plugin *libinput_plugin,
+			struct libinput_device *device,
+			struct libevdev *libevdev,
+			struct udev_device *udev_device)
+{
+	struct evdev_device *evdev = evdev_device(device);
+
+	if (libevdev_has_event_code(libevdev, EV_REL, REL_WHEEL_HI_RES) ||
+	    libevdev_has_event_code(libevdev, EV_REL, REL_HWHEEL_HI_RES))
+		return;
+
+	if (libevdev_has_event_code(libevdev, EV_REL, REL_WHEEL) ||
+	    libevdev_has_event_code(libevdev, EV_REL, REL_HWHEEL))
+		evdev_log_info(evdev,
+			       "emulating high-resolution scroll wheel events.\n");
+
+	if (libevdev_has_event_code(libevdev, EV_REL, REL_WHEEL))
+		libevdev_enable_event_code(libevdev, EV_REL, REL_WHEEL_HI_RES, NULL);
+
+	if (libevdev_has_event_code(libevdev, EV_REL, REL_HWHEEL))
+		libevdev_enable_event_code(libevdev, EV_REL, REL_HWHEEL_HI_RES, NULL);
+
+	libinput_plugin_enable_device_event_frame(libinput_plugin, device, true);
+}
+
+static void
+wheel_plugin_evdev_frame(struct libinput_plugin *libinput_plugin,
+			 struct libinput_device *device,
+			 struct evdev_frame *frame)
+{
+	size_t nevents;
+	struct evdev_event *events = evdev_frame_get_events(frame, &nevents);
+
+	for (size_t i = 0; i < nevents; i++) {
+		struct evdev_event *e = &events[i];
+		switch (evdev_usage_enum(e->usage)) {
+		case EVDEV_REL_WHEEL:
+			evdev_frame_append_one(frame,
+					       evdev_usage_from(EVDEV_REL_WHEEL_HI_RES),
+					       e->value * 120);
+			break;
+		case EVDEV_REL_HWHEEL:
+			evdev_frame_append_one(
+				frame,
+				evdev_usage_from(EVDEV_REL_HWHEEL_HI_RES),
+				e->value * 120);
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+static const struct libinput_plugin_interface interface = {
+	.device_new = wheel_plugin_device_new,
+	.evdev_frame = wheel_plugin_evdev_frame,
+};
+
+void
+libinput_mouse_plugin_wheel_lowres(struct libinput *libinput)
+{
+	_unref_(libinput_plugin) *p =
+		libinput_plugin_new(libinput, "mouse-wheel-lowres", &interface, NULL);
+}

src/libinput-plugin-mouse-wheel-lowres.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright © 2025 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include "libinput-plugin.h"
+#include "libinput.h"
+
+void
+libinput_mouse_plugin_wheel_lowres(struct libinput *libinput);

src/libinput-plugin.c

@@ -30,6 +30,7 @@
 
 #include "evdev-plugin.h"
 #include "libinput-plugin-button-debounce.h"
+#include "libinput-plugin-mouse-wheel-lowres.h"
 #include "libinput-plugin-mouse-wheel.h"
 #include "libinput-plugin-mtdev.h"
 #include "libinput-plugin-private.h"
@@ -390,6 +391,7 @@ libinput_plugin_system_load_internal_plugins(struct libinput *libinput,
 	libinput_tablet_plugin_proximity_timer(libinput);
 	libinput_tablet_plugin_eraser_button(libinput);
 	libinput_debounce_plugin(libinput);
+	libinput_mouse_plugin_wheel_lowres(libinput);
 	libinput_mouse_plugin_wheel(libinput);
 
 	/* Our own event dispatch is implemented as mini-plugin,