improve Unit according to Sprite implementation

engine/Unit.cpp

@@ -146,4 +146,12 @@ Mesh* Unit::mesh(const char* name)
 	return m_creator->lookup_mesh(c->component);
 }
 
+//-----------------------------------------------------------------------------
+Sprite*	Unit::sprite(const char* name)
+{
+	Component* c = m_component->get_component(name);
+
+	return m_creator->lookup_sprite(c->component);
+}
+
 } // namespace crown

engine/Unit.h

@@ -48,6 +48,7 @@ struct ComponentType
 		UNKNOWN,
 		CAMERA,
 		MESH,
+		SPRITE,
 		SOUND
 	};
 };
@@ -154,6 +155,7 @@ struct UnitResource
 
 class Camera;
 class Mesh;
+class Sprite;
 class World;
 
 struct Unit
@@ -180,6 +182,7 @@ struct Unit
 
 	Camera*			camera(const char* name);
 	Mesh*			mesh(const char* name);
+	Sprite*			sprite(const char* name);
 
 private: