Only send frame done to visible views

Also don't accumulate empty damage

sway/desktop/output.c

@@ -948,6 +948,11 @@ static void send_frame_done_container_iterator(struct sway_container *con,
 	if (!sway_assert(con->type == C_VIEW, "expected a view")) {
 		return;
 	}
+
+	if (!view_is_visible(con->sway_view)) {
+		return;
+	}
+
 	output_view_for_each_surface(con->sway_view, &data->root_geo,
 		send_frame_done_iterator, data);
 }
@@ -1039,6 +1044,7 @@ static void damage_surface_iterator(struct wlr_surface *surface, int sx, int sy,
 	int center_x = box.x + box.width/2;
 	int center_y = box.y + box.height/2;
 
+	if (pixman_region32_not_empty(&surface->current->surface_damage)) {
 		pixman_region32_t damage;
 		pixman_region32_init(&damage);
 		pixman_region32_copy(&damage, &surface->current->surface_damage);
@@ -1054,6 +1060,7 @@ static void damage_surface_iterator(struct wlr_surface *surface, int sx, int sy,
 			center_x, center_y);
 		wlr_output_damage_add(output->damage, &damage);
 		pixman_region32_fini(&damage);
+	}
 
 	if (whole) {
 		wlr_box_rotated_bounds(&box, rotation, &box);