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.

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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.