Parse the MOUSE_WHEEL_CLICK_ANGLE udev property if present

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>

doc/device-configuration-via-udev.dox

@@ -23,6 +23,10 @@ context. Defaults to "default".</dd>
 <dd>HW resolution and sampling frequency of a relative pointer device.
 See @ref motion_normalization for details.
 </dd>
+<dt>MOUSE_WHEEL_CLICK_ANGLE</dt>
+<dd>The angle in degrees for each click on a mouse wheel. See
+libinput_pointer_get_axis_source() for details.
+</dd>
 </dl>
 
 Below is an example udev rule to assign "seat1" to a device from vendor

src/evdev.c

@@ -577,7 +577,7 @@ evdev_process_relative(struct evdev_device *device,
 			time,
 			LIBINPUT_POINTER_AXIS_SCROLL_VERTICAL,
 			LIBINPUT_POINTER_AXIS_SOURCE_WHEEL,
-			-1 * e->value * DEFAULT_WHEEL_CLICK_ANGLE);
+			-1 * e->value * device->scroll.wheel_click_angle);
 		break;
 	case REL_HWHEEL:
 		evdev_flush_pending_event(device, time);
@@ -586,7 +586,7 @@ evdev_process_relative(struct evdev_device *device,
 			time,
 			LIBINPUT_POINTER_AXIS_SCROLL_HORIZONTAL,
 			LIBINPUT_POINTER_AXIS_SOURCE_WHEEL,
-			e->value * DEFAULT_WHEEL_CLICK_ANGLE);
+			e->value * device->scroll.wheel_click_angle);
 		break;
 	}
 }
@@ -1239,6 +1239,29 @@ evdev_tag_device(struct evdev_device *device)
 							device->udev_device);
 }
 
+static inline int
+evdev_read_wheel_click_prop(struct evdev_device *device)
+{
+	struct libinput *libinput = device->base.seat->libinput;
+	const char *prop;
+	int angle = DEFAULT_WHEEL_CLICK_ANGLE;
+
+	prop = udev_device_get_property_value(device->udev_device,
+					      "MOUSE_WHEEL_CLICK_ANGLE");
+	if (prop) {
+		angle = parse_mouse_wheel_click_angle_property(prop);
+		if (!angle) {
+			log_error(libinput,
+				  "Mouse wheel click angle '%s' is present but invalid,"
+				  "using %d degrees instead\n",
+				  device->devname,
+				  DEFAULT_WHEEL_CLICK_ANGLE);
+			angle = DEFAULT_WHEEL_CLICK_ANGLE;
+		}
+	}
+
+	return angle;
+}
 static inline int
 evdev_read_dpi_prop(struct evdev_device *device)
 {
@@ -1568,6 +1591,8 @@ evdev_device_create(struct libinput_seat *seat,
 	device->devname = libevdev_get_name(device->evdev);
 	device->scroll.threshold = 5.0; /* Default may be overridden */
 	device->scroll.direction = 0;
+	device->scroll.wheel_click_angle =
+		evdev_read_wheel_click_prop(device);
 	device->dpi = evdev_read_dpi_prop(device);
 	/* at most 5 SYN_DROPPED log-messages per 30s */
 	ratelimit_init(&device->syn_drop_limit, 30ULL * 1000, 5);

src/evdev.h

@@ -119,6 +119,9 @@ struct evdev_device {
 		/* set during device init if we want natural scrolling,
 		 * used at runtime to enable/disable the feature */
 		bool natural_scrolling_enabled;
+
+		/* angle per REL_WHEEL click in degrees */
+		int wheel_click_angle;
 	} scroll;
 
 	enum evdev_event_type pending_event;

src/libinput-util.c

@@ -171,3 +171,33 @@ parse_mouse_dpi_property(const char *prop)
 	}
 	return dpi;
 }
+
+/**
+ * Helper function to parse the MOUSE_WHEEL_CLICK_ANGLE property from udev.
+ * Property is of the form:
+ * MOUSE_WHEEL_CLICK_ANGLE=<integer>
+ * Where the number indicates the degrees travelled for each click.
+ *
+ * We skip preceding whitespaces and parse the first number seen. If
+ * multiple numbers are specified, we ignore those.
+ *
+ * @param prop The value of the udev property (without the MOUSE_WHEEL_CLICK_ANGLE=)
+ * @return The angle of the wheel (may be negative) or 0 on error.
+ */
+int
+parse_mouse_wheel_click_angle_property(const char *prop)
+{
+	int angle = 0,
+	    nread = 0;
+
+	while(*prop != 0 && *prop == ' ')
+		prop++;
+
+	sscanf(prop, "%d%n", &angle, &nread);
+	if (nread == 0 || angle == 0 || abs(angle) > 360)
+		return 0;
+	if (prop[nread] != ' ' && prop[nread] != '\0')
+		return 0;
+
+        return angle;
+}

src/libinput-util.h

@@ -297,5 +297,6 @@ void ratelimit_init(struct ratelimit *r, uint64_t ival_ms, unsigned int burst);
 enum ratelimit_state ratelimit_test(struct ratelimit *r);
 
 int parse_mouse_dpi_property(const char *prop);
+int parse_mouse_wheel_click_angle_property(const char *prop);
 
 #endif /* LIBINPUT_UTIL_H */

test/misc.c

@@ -531,7 +531,7 @@ END_TEST
 
 struct parser_test {
 	char *tag;
-	int expected_dpi;
+	int expected_value;
 };
 
 START_TEST(dpi_parser)
@@ -565,7 +565,36 @@ START_TEST(dpi_parser)
 
 	for (i = 0; tests[i].tag != NULL; i++) {
 		dpi = parse_mouse_dpi_property(tests[i].tag);
-		ck_assert_int_eq(dpi, tests[i].expected_dpi);
+		ck_assert_int_eq(dpi, tests[i].expected_value);
+	}
+}
+END_TEST
+
+START_TEST(wheel_click_parser)
+{
+	struct parser_test tests[] = {
+		{ "1", 1 },
+		{ "10", 10 },
+		{ "-12", -12 },
+		{ "360", 360 },
+		{ "66 ", 66 },
+		{ "   100 ", 100 },
+
+		{ "0", 0 },
+		{ "-0", 0 },
+		{ "a", 0 },
+		{ "10a", 0 },
+		{ "10-", 0 },
+		{ "sadfasfd", 0 },
+		{ "361", 0 },
+		{ NULL, 0 }
+	};
+
+	int i, angle;
+
+	for (i = 0; tests[i].tag != NULL; i++) {
+		angle = parse_mouse_wheel_click_angle_property(tests[i].tag);
+		ck_assert_int_eq(angle, tests[i].expected_value);
 	}
 }
 END_TEST
@@ -582,6 +611,7 @@ int main (int argc, char **argv) {
 	litest_add_no_device("misc:matrix", matrix_helpers);
 	litest_add_no_device("misc:ratelimit", ratelimit_helpers);
 	litest_add_no_device("misc:dpi parser", dpi_parser);
+	litest_add_no_device("misc:wheel click parser", wheel_click_parser);
 
 	return litest_run(argc, argv);
 }