Displaying data graphically (Ultrasonic radar)

[Alex83UK]

Hi GremlinSA, thanks to your explanations and article I finally understood the concept of double buffering (or at least I think so ).
However I the program is still running slow :/
I have tried your method of drawing as you wrote on your last post but the scan line went really funny and the speed was the same as it was before.
Do you mind having a look at my code and see if I missing something? I'd really appreciate that!

Thanks in advance!