Hello Professor!

Thank you for all that you have shared and helped people understand these concepts with more clarity. I recently started looking into graphics on Windows Mobile phones and thanks to you I was able to come up with a colliding marbles program pretty quickly. If you are interested here is the link:

http://geekswithblogs.net/TechTwaddle/archive/2009/07/16/bouncingcolliding-marbles-directdraw-part-7.aspx

Sometimes there is a problem with the program. The balls will stick or completely disappear from the screen. But it happens very rarely, maybe around 1 in 30 times. I haven't yet looked deeply into the problem. Well, that is my next task (:

Thank you again and I really appreciate your work.
Prabhu