buffer: add addon set

This allows wlr_buffer users to extend it with tjeir own state.

include/wlr/types/wlr_buffer.h

@@ -12,6 +12,7 @@
 #include <pixman.h>
 #include <wayland-server-core.h>
 #include <wlr/render/dmabuf.h>
+#include <wlr/util/addon.h>
 
 struct wlr_buffer;
 struct wlr_renderer;
@@ -67,6 +68,8 @@ struct wlr_buffer {
 		struct wl_signal destroy;
 		struct wl_signal release;
 	} events;
+
+	struct wlr_addon_set addons;
 };
 
 struct wlr_buffer_resource_interface {

types/wlr_buffer.c

@@ -21,6 +21,7 @@ void wlr_buffer_init(struct wlr_buffer *buffer,
 	buffer->height = height;
 	wl_signal_init(&buffer->events.destroy);
 	wl_signal_init(&buffer->events.release);
+	wlr_addon_set_init(&buffer->addons);
 }
 
 static void buffer_consider_destroy(struct wlr_buffer *buffer) {
@@ -31,6 +32,7 @@ static void buffer_consider_destroy(struct wlr_buffer *buffer) {
 	assert(!buffer->accessing_data_ptr);
 
 	wlr_signal_emit_safe(&buffer->events.destroy, NULL);
+	wlr_addon_set_finish(&buffer->addons);
 
 	buffer->impl->destroy(buffer);
 }