unity3d 控制OnGUI

有时我们想要在一些按钮或鼠标事件之后在让OnGUI画出里面的东西、
bool down = false;
void OnGUI()
{
  if (down)
      GUILayout.Label("had mouse down");
 
  if (Event.current.type == EventType.MouseDown)
      down = true;
}

参考：http://forum.unity3d.com/threads/29058-error-with-no-side-effects