input: prevent cursor notifications from pointer and tablet tool

... at the same time. Omit cursor notifications from
a pointer when a tablet tool (stylus/pen) is in
proximity. We expect to get cursor notifications
from the tablet tool instead.

include/input/tablet-tool.h

@@ -14,6 +14,7 @@ struct drawing_tablet_tool {
 		struct wl_listener set_cursor;
 		struct wl_listener destroy;
 	} handlers;
+	struct wl_list link; /* seat.tablet_tools */
 };
 
 void tablet_tool_init(struct seat *seat,

include/labwc.h

@@ -193,6 +193,8 @@ struct seat {
 	struct wl_listener touch_motion;
 	struct wl_listener touch_frame;
 
+	struct wl_list tablet_tools;
+
 	struct wl_listener constraint_commit;
 	struct wl_listener pressed_surface_destroy;
 

src/input/cursor.c

@@ -17,6 +17,7 @@
 #include "idle.h"
 #include "input/gestures.h"
 #include "input/touch.h"
+#include "input/tablet-tool.h"
 #include "labwc.h"
 #include "layers.h"
 #include "menu/menu.h"
@@ -140,6 +141,22 @@ request_cursor_notify(struct wl_listener *listener, void *data)
 		return;
 	}
 
+	/*
+	 * Omit cursor notifications from a pointer when a tablet
+	 * tool (stylus/pen) is in proximity. We expect to get cursor
+	 * notifications from the tablet tool instead.
+	 * Receiving cursor notifications from pointer and tablet tool at
+	 * the same time is a side effect of also setting pointer focus
+	 * when a tablet tool enters proximity on a tablet-capable surface.
+	 * See also `notify_motion()` in `input/tablet.c`.
+	 */
+	struct drawing_tablet_tool *tool;
+	wl_list_for_each(tool, &seat->tablet_tools, link) {
+		if (tool->tool_v2->focused_surface) {
+			return;
+		}
+	}
+
 	/*
 	 * This event is raised by the seat when a client provides a cursor
 	 * image

src/input/tablet-tool.c

@@ -40,6 +40,7 @@ handle_destroy(struct wl_listener *listener, void *data)
 	struct drawing_tablet_tool *tool =
 		wl_container_of(listener, tool, handlers.destroy);
 
+	wl_list_remove(&tool->link);
 	wl_list_remove(&tool->handlers.set_cursor.link);
 	wl_list_remove(&tool->handlers.destroy.link);
 	free(tool);
@@ -65,4 +66,5 @@ tablet_tool_init(struct seat *seat,
 		wlr_tablet_tool->wheel ? " wheel" : "");
 	CONNECT_SIGNAL(tool->tool_v2, &tool->handlers, set_cursor);
 	CONNECT_SIGNAL(wlr_tablet_tool, &tool->handlers, destroy);
+	wl_list_insert(&seat->tablet_tools, &tool->link);
 }

src/seat.c

@@ -553,6 +553,8 @@ seat_init(struct server *server)
 	}
 	wlr_cursor_attach_output_layout(seat->cursor, server->output_layout);
 
+	wl_list_init(&seat->tablet_tools);
+
 	input_handlers_init(seat);
 }