Add scroll method libinput option

<libinput>
  <device>
    <scrollMethod>none|twofinger|edge</scrollMethod>
  </device>
</libinput>

Fixes: #2766

docs/labwc-config.5.scd

@@ -941,6 +941,7 @@ extending outward from the snapped edge.
     <middleEmulation></middleEmulation>
     <disableWhileTyping></disableWhileTyping>
     <clickMethod></clickMethod>
+    <scrollMethod></scrollMethod>
     <sendEventsMode></sendEventsMode>
     <calibrationMatrix></calibrationMatrix>
     <scrollFactor>1.0</scrollFactor>
@@ -1035,6 +1036,19 @@ extending outward from the snapped edge.
 
 	The default method depends on the touchpad hardware.
 
+*<libinput><device><scrollMethod>* [none|twofinger|edge]
+	Configure the method by which physical movements on a touchpad are
+	mapped to scroll events.
+
+	The scroll methods available are:
+	- *twofinger* - Scroll by two fingers being placed on the surface of the
+	  touchpad, then moving those fingers vertically or horizontally.
+	- *edge* - Scroll by moving a single finger along the right edge
+	  (vertical scroll) or bottom edge (horizontal scroll).
+	- *none* - No scroll events will be produced.
+
+	The default method depends on the touchpad hardware.
+
 *<libinput><device><sendEventsMode>* [yes|no|disabledOnExternalMouse]
 	Optionally enable or disable sending any device events.
 

docs/rc.xml.all

@@ -635,6 +635,7 @@
       <middleEmulation></middleEmulation>
       <disableWhileTyping></disableWhileTyping>
       <clickMethod></clickMethod>
+      <scrollMethod></scrollMethod>
       <sendEventsMode></sendEventsMode>
       <calibrationMatrix></calibrationMatrix>
       <scrollFactor>1.0</scrollFactor>

include/config/libinput.h

@@ -29,6 +29,7 @@ struct libinput_category {
 	int middle_emu;                 /* -1 or libinput_config_middle_emulation_state */
 	int dwt;                        /* -1 or libinput_config_dwt_state */
 	int click_method;               /* -1 or libinput_config_click_method */
+	int scroll_method;              /* -1 or libinput_config_scroll_method */
 	int send_events_mode;           /* -1 or libinput_config_send_events_mode */
 	bool have_calibration_matrix;
 	double scroll_factor;

src/config/libinput.c

@@ -24,6 +24,7 @@ libinput_category_init(struct libinput_category *l)
 	l->middle_emu = -1;
 	l->dwt = -1;
 	l->click_method = -1;
+	l->scroll_method = -1;
 	l->send_events_mode = -1;
 	l->have_calibration_matrix = false;
 	l->scroll_factor = 1.0;

src/config/rcxml.c

@@ -810,6 +810,19 @@ fill_libinput_category(char *nodename, char *content, struct parser_state *state
 		} else {
 			wlr_log(WLR_ERROR, "invalid clickMethod");
 		}
+	} else if (!strcasecmp(nodename, "scrollMethod")) {
+		if (!strcasecmp(content, "none")) {
+			state->current_libinput_category->scroll_method =
+				LIBINPUT_CONFIG_SCROLL_NO_SCROLL;
+		} else if (!strcasecmp(content, "edge")) {
+			state->current_libinput_category->scroll_method =
+				LIBINPUT_CONFIG_SCROLL_EDGE;
+		} else if (!strcasecmp(content, "twofinger")) {
+			state->current_libinput_category->scroll_method =
+				LIBINPUT_CONFIG_SCROLL_2FG;
+		} else {
+			wlr_log(WLR_ERROR, "invalid scrollMethod");
+		}
 	} else if (!strcasecmp(nodename, "sendEventsMode")) {
 		state->current_libinput_category->send_events_mode =
 			get_send_events_mode(content);

src/seat.c

@@ -233,6 +233,17 @@ configure_libinput(struct wlr_input_device *wlr_input_device)
 		libinput_device_config_click_set_method(libinput_dev, dc->click_method);
 	}
 
+	if (dc->scroll_method < 0) {
+		wlr_log(WLR_INFO, "scroll method not configured");
+	} else if (dc->scroll_method != LIBINPUT_CONFIG_SCROLL_NO_SCROLL
+			&& (libinput_device_config_scroll_get_methods(libinput_dev)
+				& dc->scroll_method) == 0) {
+		wlr_log(WLR_INFO, "scroll method not supported");
+	} else {
+		wlr_log(WLR_INFO, "scroll method configured");
+		libinput_device_config_scroll_set_method(libinput_dev, dc->scroll_method);
+	}
+
 	if ((dc->send_events_mode != LIBINPUT_CONFIG_SEND_EVENTS_ENABLED
 			&& (libinput_device_config_send_events_get_modes(libinput_dev)
 				& dc->send_events_mode) == 0)