Add mouse emulation for touch devices (#2277)

docs/labwc-config.5.scd

@@ -690,7 +690,7 @@ extending outward from the snapped edge.
 ## TOUCH
 
 ```
-<touch deviceName="" mapToOutput="" />
+<touch deviceName="" mapToOutput="" mouseEmulation="no"/>
 ```
 
 *<touch deviceName="" />*
@@ -704,6 +704,10 @@ extending outward from the snapped edge.
 	Direct cursor movement to a specified output. If the compositor is
 	running in nested mode, this does not take effect.
 
+*<touch mouseEmulation="" />*
+	If mouseEmulation is enabled, all touch up/down/motion events are
+	translated to mouse button and motion events.
+
 ## TABLET
 
 ```

docs/rc.xml.all

@@ -537,8 +537,11 @@
 
     Direct cursor movement to a specified output. If the compositor is
     running in nested mode, this does not take effect.
+
+    If mouseEmulation is enabled, all touch up/down/motion events are
+    translated to mouse button and motion events.
   -->
-  <touch deviceName="" mapToOutput="" />
+  <touch deviceName="" mapToOutput="" mouseEmulation="no"/>
 
   <!--
     The tablet cursor movement can be restricted to a single output.

include/config/touch.h

@@ -8,6 +8,7 @@
 struct touch_config_entry {
 	char *device_name;
 	char *output_name;
+	bool force_mouse_emulation;
 
 	struct wl_list link;     /* struct rcxml.touch_configs */
 };

src/config/rcxml.c

@@ -633,6 +633,8 @@ fill_touch(char *nodename, char *content)
 		current_touch->device_name = xstrdup(content);
 	} else if (!strcasecmp(nodename, "mapToOutput.touch")) {
 		current_touch->output_name = xstrdup(content);
+	} else if (!strcasecmp(nodename, "mouseEmulation.touch")) {
+		set_bool(content, &current_touch->force_mouse_emulation);
 	} else {
 		wlr_log(WLR_ERROR, "Unexpected data in touch parser: %s=\"%s\"",
 			nodename, content);

src/input/touch.c

@@ -24,6 +24,17 @@ static struct wlr_surface*
 touch_get_coords(struct seat *seat, struct wlr_touch *touch, double x, double y,
 		double *x_offset, double *y_offset)
 {
+	/*
+	 * Do not return a surface when mouse emulation is enforced. Not
+	 * having a surface will trigger the fallback to cursor move/button
+	 * emulation in the touch signal handlers.
+	 */
+	struct touch_config_entry *config_entry =
+		touch_find_config_for_device(touch->base.name);
+	if (config_entry && config_entry->force_mouse_emulation) {
+		return NULL;
+	}
+
 	/* Convert coordinates: first [0, 1] => layout, then layout => surface */
 	double lx, ly;
 	wlr_cursor_absolute_to_layout_coords(seat->cursor, &touch->base,
@@ -93,7 +104,7 @@ handle_touch_down(struct wl_listener *listener, void *data)
 
 	/* Compute layout => surface offset and save for this touch point */
 	struct touch_point *touch_point = znew(*touch_point);
-	double x_offset, y_offset;
+	double x_offset = 0.0, y_offset = 0.0;
 	touch_point->surface = touch_get_coords(seat, event->touch,
 			event->x, event->y, &x_offset, &y_offset);
 	touch_point->touch_id = event->touch_id;