scene: add wlr_scene_node_toggle

This allows compositors to easily enable or disable a scene-graph node.
This can be used to show/hide a surface when the xdg_surface is
mapped/unmapped.

include/wlr/types/wlr_scene.h

@@ -35,6 +35,7 @@ struct wlr_scene_node_state {
 
 	struct wl_list children; // wlr_scene_node_state.link
 
+	bool enabled;
 	int x, y; // relative to parent
 };
 
@@ -68,6 +69,11 @@ struct wlr_scene_surface {
  * Immediately destroy the scene-graph node.
  */
 void wlr_scene_node_destroy(struct wlr_scene_node *node);
+/**
+ * Enable or disable this node. If a node is disabled, all of its children are
+ * implicitly disabled as well.
+ */
+void wlr_scene_node_set_enabled(struct wlr_scene_node *node, bool enabled);
 /**
  * Set the position of the node relative to its parent.
  */

types/wlr_scene.c

@@ -21,6 +21,7 @@ static struct wlr_scene_surface *scene_surface_from_node(
 static void scene_node_state_init(struct wlr_scene_node_state *state) {
 	wl_list_init(&state->children);
 	wl_list_init(&state->link);
+	state->enabled = true;
 }
 
 static void scene_node_state_finish(struct wlr_scene_node_state *state) {
@@ -108,6 +109,10 @@ struct wlr_scene_surface *wlr_scene_surface_create(struct wlr_scene_node *parent
 	return scene_surface;
 }
 
+void wlr_scene_node_set_enabled(struct wlr_scene_node *node, bool enabled) {
+	node->state.enabled = enabled;
+}
+
 void wlr_scene_node_set_position(struct wlr_scene_node *node, int x, int y) {
 	node->state.x = x;
 	node->state.y = y;
@@ -132,6 +137,10 @@ void wlr_scene_node_place_below(struct wlr_scene_node *node,
 static void scene_node_for_each_surface(struct wlr_scene_node *node,
 		int lx, int ly, wlr_surface_iterator_func_t user_iterator,
 		void *user_data) {
+	if (!node->state.enabled) {
+		return;
+	}
+
 	lx += node->state.x;
 	ly += node->state.y;