scene_graph: Introduce sway_scene_descriptor

Across a wayland compositor, there are multiple shells: It can be
a toplevel, or a layer_shell, or even something more meta like a drag
icon or highlight indicators when dragging windows around.

This object lets us store values that represent these modes of operation
and keep track of what object is being represented.

2 files changed, 67 insertions, 0 deletions

diff --git a/sway/meson.build b/sway/meson.build
index 3abd778d..26251e58 100644
--- a/sway/meson.build
+++ b/sway/meson.build
@@ -8,6 +8,7 @@ sway_sources = files(
 	'lock.c',
 	'main.c',
 	'realtime.c',
+	'scene_descriptor.c',
 	'server.c',
 	'swaynag.c',
 	'xdg_activation_v1.c',
diff --git a/sway/scene_descriptor.c b/sway/scene_descriptor.c
new file mode 100644
index 00000000..a30d4664
--- /dev/null
+++ b/sway/scene_descriptor.c
@@ -0,0 +1,66 @@
+#include <stdlib.h>
+#include <wlr/util/addon.h>
+#include "log.h"
+#include "sway/scene_descriptor.h"
+
+struct scene_descriptor {
+	void *data;
+	struct wlr_addon addon;
+};
+
+static const struct wlr_addon_interface addon_interface;
+
+static struct scene_descriptor *scene_node_get_descriptor(
+		struct wlr_scene_node *node, enum sway_scene_descriptor_type type) {
+	struct wlr_addon *addon = wlr_addon_find(&node->addons, (void *)type, &addon_interface);
+	if (!addon) {
+		return NULL;
+	}
+
+	struct scene_descriptor *desc = wl_container_of(addon, desc, addon);
+	return desc;
+}
+
+static void descriptor_destroy(struct scene_descriptor *desc) {
+	wlr_addon_finish(&desc->addon);
+	free(desc);
+}
+
+void *scene_descriptor_try_get(struct wlr_scene_node *node,
+		enum sway_scene_descriptor_type type) {
+	struct scene_descriptor *desc = scene_node_get_descriptor(node, type);
+	if (!desc) {
+		return NULL;
+	}
+
+	return desc->data;
+}
+
+void scene_descriptor_destroy(struct wlr_scene_node *node,
+		enum sway_scene_descriptor_type type) {
+	struct scene_descriptor *desc = scene_node_get_descriptor(node, type);
+	descriptor_destroy(desc);
+}
+
+static void addon_handle_destroy(struct wlr_addon *addon) {
+	struct scene_descriptor *desc = wl_container_of(addon, desc, addon);
+	descriptor_destroy(desc);
+}
+
+static const struct wlr_addon_interface addon_interface = {
+	.name = "sway_scene_descriptor",
+	.destroy = addon_handle_destroy,
+};
+
+bool scene_descriptor_assign(struct wlr_scene_node *node,
+		enum sway_scene_descriptor_type type, void *data) {
+	struct scene_descriptor *desc = calloc(1, sizeof(*desc));
+	if (!desc) {
+		sway_log(SWAY_ERROR, "Could not allocate a scene descriptor");
+		return false;
+	}
+
+	wlr_addon_init(&desc->addon, &node->addons, (void *)type, &addon_interface);
+	desc->data = data;
+	return true;
+}