Design Question: Delegation vs. callbacks

[Henning Hasemann]

Say I have basically three classes which form my problem:
Thing, Area and Animation.

A thing is something on the screen you can interact with, and area just
defines a number of pixels (there are rectangular areas as well as
bitmasks), an animation is something you can actually see.

Now a thing has a Position somewhere on the screen and it has an area,
so you can check if it was clicked, also it will probably have an
animation from wich an area can be get with the method boundingBox().

Say Area has a method isIn(x,y) which says if the coordinate is inside
the area. Now I have two possibilities:

"Delegation":
  Thing's area is private but Thing has its own isIn(x,y) method
  where it substracts its own method and then delegates the call
  to area, so area doesnt have a position at all.
  Similar approach then for animation and a render() method.

  cons:
  - I cant position a plain animation on the screen without a thing or
    an other wrapper class.
  - This pattern drastically flattens structure: thing re-implements
    lot of the methods of area and animation with the delegates,
    but *does not* inherit from their possible interfaces.
    (If it would, the isIn() etc... methods would have different
    semantics: in thing isIn would accept a screen-position whereas
    in area isIn would operate on a position relative to the area)

"Callbacks":
  Everything operates with absolute screen-coordinates and area as well
  as animation have function pointers / delegates to check, what the
  position of the thing is, they belong to.

  cons:
  - the callbacks feel somewhat "magical", especially when you consider
    the bounding box stuff: the area returned by .boundingBox() would
    look up its position from the animation wheres the animation would
    look at the thing.
    It might feel weird that the .position attribute of something can
    change, just because I change a totally different thing.

What would you choose? Do you see other alternatives to solve this?

TIA
Henning






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