You can use those, but then you have to call ValidateRect manually.

Thanks Airbatz…

Ok i will try first to translate this program in Oxygen Basic ,and if there work then should work in C too..i hope!

@Shaarigan 

I have taken a  look at the links but it will take a while before I can make much sense of it as a whole. Currently I'm just modifying the program step by step to see how it affects the performance. Visibly nothing is different. Thanks for your input, I will read up on WM_PAINT…