Do anyone know how to let the drawing curve at the picture more smooth?

[susanluck159]

Do anyone know how to let the drawing curve at the picture more smooth??
http://i178.photobucket.com/albums/w264/susanluck159/qqq.jpg

[eastmoon]

Bezier curve
https://en.wikipedia.org/wiki/B%C3%A9zier_curve

[susanluck159]

thank you,
but I want to know where to chang the value in the source code to let the drawing curve more smooth.