32. The computer program product of claim 31 , wherein moving the element comprises: determining a set of candidate positions for which a projection of the base joint onto screen space is located at the starting point or the ending point of the stroke, and a projection of the tip joint onto screen space is located at the starting point or the ending point of the stroke; and selecting a candidate position from the set based at least in part on the direction of the stroke.
32. The computer program product of claim 31 , wherein moving the element comprises: determining a set of candidate positions for which a projection of the base joint onto screen space is located at the starting point or the ending point of the stroke, and a projection of the tip joint onto screen space is located at the starting point or the ending point of the stroke; and selecting a candidate position from the set based at least in part on the direction of the stroke. 33. The computer program product of claim 32 , wherein the direction of the stroke indicates whether the base joint of the selected position is closer to the screen space than the tip point of the selected position.