Interactive GUI Patch/Tessellation

Hi everybody

I'm trying to design a GUI where the user is able to draw a series of connected patches (a tessellation) over a background image and then assign a value to each of them.

I'm trying to figure out which is the best way to achieve this.

I found the impoly function that is very close to what I need for the first patch. However, when I draw the second polygon I would like to be able to "attach" it to the previous one without having to repeat the shared edges. Moreover I would like to be able to "snap" to the existing vertices in order to avoid nasty holes in the tessellation.

I was thinking to a couple of solutions:

• modify the impoly function to introduce this behavior, but this isn't very easy.
• define some objects that exploit the impoly function when edited and then "freeze" in a patch object.

Do you have suggestions/ideas?

Thank you very much regards Luca