+#ifndef MSP_GAME_TRANSFORMPROPAGATOR_H_
+#define MSP_GAME_TRANSFORMPROPAGATOR_H_
+
+#include "eventobserver.h"
+#include "handle.h"
+#include "system.h"
+
+namespace Msp::Game {
+
+class Entity;
+class Transform;
+
+class TransformPropagator: public System
+{
+private:
+ struct ParentedTransform
+ {
+ Handle<Transform> transform;
+ Handle<Transform> parent;
+ };
+
+ EventObserver observer;
+ std::vector<ParentedTransform> transforms;
+ bool transforms_dirty = true;
+
+public:
+ TransformPropagator(Stage &);
+
+ void tick(Time::TimeDelta) override;
+
+private:
+ void rebuild_transform_order();
+ void rebuild_transform_order(Handle<Entity>, Handle<Transform>);
+};
+
+} // namespace Msp::Game
+
+#endif