If you would have shown as the error message of the linker, it would be a lot easier to help.

Anyway, in this simple case I guess you just forgot the WaveFormDisplay:: in the method signature of your implementation to the linker does not know that the three mouse-event-handler belong to your class.

But also some comments to your code:
  1. Why do you "accept" the mouse-events already?
  2. Although it is good to write documentation, you "document the obvious": http://freeworld.thc.org/root/phun/unmaintain.html