How to "drag a line" in drawing area?

["roronoa zorro" <roronoa52zorro hotmail com>]

Hello there:

Does anybody know how to implement a drag-line function with drawing area? 
What i want is to draw a line from the start point to the current point in 
motion_notify_event. However, if i add the draw method in 
motion_notify_event it will draw lines from the start point to all the 
points that the mouse passes by. Is is possible to delete the previous 
lines and only display the connection with the current one?

Any help is great! 

Guo

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