This is no real lite-c contribution, so sorry.
But I thought that one would most likely search for this in here.

Okay. As title says it. Algorithms to calculate intersections of various shapes:
http://www.realtimerendering.com/intersections.html

I was there just recently Have you been working on custom collision detection?

This is really interesting and useful, thank you!

No, more collision avoidance.
What also might help is the seperate axis test: http://stackoverflow.com/questions/115426/algorithm-to-detect-intersection-of-two-rectangles