refactor: tower add event processing

include/render/WorldRenderer.h

@@ -23,7 +23,7 @@ class ClientGame;
 
 namespace render {
 
-class WorldRenderer {
+class WorldRenderer : public game::WorldListener {
 private:
     client::ClientGame* m_Client;
     Renderer* m_Renderer;
@@ -58,6 +58,11 @@ public:
 
     void moveCam(float relativeX, float relativeY, float aspectRatio);
     void changeZoom(float zoom);
+
+    // WorldListener
+
+    virtual void OnTowerAdd(game::TowerPtr tower);
+    virtual void OnTowerRemove(game::TowerPtr tower);
 private:
     void click();
     void renderWorld() const;