iOS: make pen drawing like Bamboo application

I am making an ipad application, using GLPaint from Apple source code. I have done the drawing but I don't like my pen effect. I would like to do it as the same with Bamboo application (free) on Apple Store. I wonder to make this pen style, I need texture and algorithm to make the pen width based on the speed of dra开发者_StackOverflowwing.

Do you have any ideas and samples for me to look. Thank you.

Please use this link and download source code from here

And set width what you want on touches moved method on line setLineWidth,

Currently there is 5.