Then, it will take a lot of time and explanation (and I have no idea how to make it without a "framework" ).

Anyway, the work is the same in any case:

  1. Keep two bit-maps that contains the foreground and the background.
  2. Upload them and use the "foreground" to hide the "background", but don't remove them from "system" memory.
  3. Now, as user moves the mouse, make "foreground" bitmap pixels transparent and upload it, substituting the old foreground (i.e., use the same GL ID).
  4. Repeat.