Oh, wouldn't they have to define such an area for the objects that would be to be hit? (that is: wouldn't the movement of an object A not just check for intersections with areas of other objects?). And if not: The object would still have to post-step through the line between the last frame and the current to check for the real colliding point (since even if the check for intersection was made: the object A would still have flewn through the object B when the callback would be called in A) (realising now that the position could easily be passed to that callback). But nevertheless: I don't really see any performance improvement in using those areas instead of a Find_OnLine/Find_AtPoint every frame - I have to grant that it would be "easier" for the scripter to use, though