gpolygon

I have been searching everywhere but I could not find an answer. I need to have drawing resizable polygons with mouse interaction but I do not want irregular, overlapping or intersecting polygons in the end. Here is a simple example of drawing resizable polygons http://www.wolfpil.de/polygon.html You can easily create & resize polygons which is great. But I need an extra functionality to detect intersections and NOT allowing weird looking shapes/polygons. You can see the problem in this video: http://www.youtube.com/watch?v=zou2jcGM8zw The only solution for that problem I found at http://www