====== Image map ======

Once you start out with 2D data representation like mindmaps, for sure you are going to want image maps as well.

Basicly use an image as background and render interactive objects on top of it.
Think rectangles and circles to "activate" certain parts of the image.

Advanced exaple might be putting flags on a map.
.. but small circles can just as well be used for that.

At least make sure that there are no image maps where it is hidden
what is clickable and what is not. Just draw clear objects over the image.
This keeps the thing transparent.

Small canvas engine for Cairo could fix this.
Define rectangle and circle object.
Put callbacks in the engine for left/right mouse clicks and for mouse-over.

Good first step towards mindmap.
Mindmap could use the same engine but add connections.
