seat: add wlr_seat_touch_notify_clear_focus

This is needed for cases where the touch operation goes over a region
where no surfaces are present. In this case, we'd want to notify the
touch grabs (for example DnD grabs) that no focus is currently focused.

include/wlr/types/wlr_seat.h

@@ -140,6 +140,8 @@ struct wlr_touch_grab_interface {
 	// Send wl_touch.cancel
 	void (*wl_cancel)(struct wlr_seat_touch_grab *grab,
 			struct wlr_seat_client *seat_client);
+	void (*clear_focus)(struct wlr_seat_touch_grab *grab, uint32_t time_msec,
+			struct wlr_touch_point *point);
 };
 
 /**
@@ -685,6 +687,8 @@ void wlr_seat_touch_notify_cancel(struct wlr_seat *seat,
 		struct wlr_seat_client *seat_client);
 
 void wlr_seat_touch_notify_frame(struct wlr_seat *seat);
+void wlr_seat_touch_notify_clear_focus(struct wlr_seat *seat,
+		uint32_t time_msec, int32_t touch_id);
 
 /**
  * How many touch points are currently down for the seat.

types/data_device/wlr_drag.c

@@ -334,6 +334,12 @@ static void drag_handle_touch_cancel(struct wlr_seat_touch_grab *grab) {
 	drag_destroy(drag);
 }
 
+static void drag_handle_clear_focus(struct wlr_seat_touch_grab *grab, uint32_t time_msec,
+		struct wlr_touch_point *point) {
+	struct wlr_drag *drag = grab->data;
+	drag_set_focus(drag, NULL, 0, 0);
+}
+
 static const struct wlr_touch_grab_interface
 		data_device_touch_drag_interface = {
 	.down = drag_handle_touch_down,
@@ -341,6 +347,7 @@ static const struct wlr_touch_grab_interface
 	.motion = drag_handle_touch_motion,
 	.enter = drag_handle_touch_enter,
 	.cancel = drag_handle_touch_cancel,
+	.clear_focus = drag_handle_clear_focus,
 };
 
 static void drag_handle_keyboard_enter(struct wlr_seat_keyboard_grab *grab,

types/seat/wlr_seat_touch.c

@@ -44,6 +44,12 @@ static void default_touch_wl_cancel(struct wlr_seat_touch_grab *grab,
 	wlr_seat_touch_send_cancel(grab->seat, seat_client);
 }
 
+static void default_touch_clear_focus(struct wlr_seat_touch_grab *grab, uint32_t time_msec,
+		struct wlr_touch_point *point) {
+	wlr_seat_touch_point_clear_focus(grab->seat, time_msec, point->touch_id);
+}
+
+
 const struct wlr_touch_grab_interface default_touch_grab_impl = {
 	.down = default_touch_down,
 	.up = default_touch_up,
@@ -52,6 +58,7 @@ const struct wlr_touch_grab_interface default_touch_grab_impl = {
 	.frame = default_touch_frame,
 	.cancel = default_touch_cancel,
 	.wl_cancel = default_touch_wl_cancel,
+	.clear_focus = default_touch_clear_focus,
 };
 
 
@@ -256,6 +263,19 @@ void wlr_seat_touch_notify_cancel(struct wlr_seat *seat,
 	}
 }
 
+void wlr_seat_touch_notify_clear_focus(struct wlr_seat *seat,
+		uint32_t time, int32_t touch_id) {
+	struct wlr_seat_touch_grab *grab = seat->touch_state.grab;
+	struct wlr_touch_point *point = wlr_seat_touch_get_point(seat, touch_id);
+	if (!point) {
+		return;
+	}
+
+	if (grab->interface->clear_focus) {
+		grab->interface->clear_focus(grab, time, point);
+	}
+}
+
 static void handle_point_focus_destroy(struct wl_listener *listener,
 		void *data) {
 	struct wlr_touch_point *point =

types/xdg_shell/wlr_xdg_popup.c

@@ -174,13 +174,19 @@ static void xdg_touch_grab_cancel(struct wlr_seat_touch_grab *grab) {
 	wlr_seat_touch_end_grab(grab->seat);
 }
 
+static void xdg_touch_grab_clear_focus(struct wlr_seat_touch_grab *grab, uint32_t time_msec,
+		struct wlr_touch_point *point) {
+	wlr_seat_touch_point_clear_focus(grab->seat, time_msec, point->touch_id);
+}
+
 static const struct wlr_touch_grab_interface xdg_touch_grab_impl = {
 	.down = xdg_touch_grab_down,
 	.up = xdg_touch_grab_up,
 	.motion = xdg_touch_grab_motion,
 	.enter = xdg_touch_grab_enter,
 	.frame = xdg_touch_grab_frame,
-	.cancel = xdg_touch_grab_cancel
+	.cancel = xdg_touch_grab_cancel,
+	.clear_focus = xdg_touch_grab_clear_focus,
 };
 
 static void destroy_xdg_popup_grab(struct wlr_xdg_popup_grab *xdg_grab) {