input/pointer: notify compositor when constraint region changes

This allows a compositor to know when warping back into the region is
appropriate.

Refs swaywm/sway#5268.

include/wlr/types/wlr_pointer_constraints_v1.h

@@ -57,6 +57,11 @@ struct wlr_pointer_constraint_v1 {
 	struct wl_list link; // wlr_pointer_constraints_v1::constraints
 
 	struct {
+		/**
+		 * Called when a pointer constraint's region is updated,
+		 * post-surface-commit.
+		 */
+		struct wl_signal set_region;
 		struct wl_signal destroy;
 	} events;
 

types/wlr_pointer_constraints_v1.c

@@ -116,6 +116,7 @@ static void pointer_constraint_commit(
 	}
 	constraint->current.committed |= constraint->pending.committed;
 
+	bool updated_region = !!constraint->pending.committed;
 	constraint->pending.committed = 0;
 
 	pixman_region32_clear(&constraint->region);
@@ -126,6 +127,10 @@ static void pointer_constraint_commit(
 		pixman_region32_copy(&constraint->region,
 			&constraint->surface->input_region);
 	}
+
+	if (updated_region) {
+		wlr_signal_emit_safe(&constraint->events.set_region, NULL);
+	}
 }
 
 static void handle_surface_commit(struct wl_listener *listener, void *data) {
@@ -209,6 +214,7 @@ static void pointer_constraint_create(struct wl_client *client,
 	constraint->type = type;
 	constraint->pointer_constraints = pointer_constraints;
 
+	wl_signal_init(&constraint->events.set_region);
 	wl_signal_init(&constraint->events.destroy);
 
 	pixman_region32_init(&constraint->region);