Please give me some suggestion about my application

["Lazy Fox" <lazy fox wu gmail com>]

 I want to draw a loopback-able dynamic curve, just like the following picture:
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/18030.jpg

The curve is keeping going, from left to right. When reach the right border,
it will loopback to the left border, and do this again and again.

But, when the curve loopback to the left border, the existent drawing will not
be erased immediately. Instead, the older drawing will be erased step by step,
where the new curve is drawing.

Considering the efficiency. In this case, which widget should I draw on?
How can I erase the image step by step,
not erase all of it? Which function should I use?

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