I am making a 2D physics based game using Box2D for Physics and SDL for Graphics.

I need to plot a collision line along the path of a ball(in linear trajectory) as it moves. The line should not collide with the plotting ball but other

balls(which are also plotting lines). Also if the plotting ball collides with an object, it should stop plotting that line and begin plotting another, and should be collidable with the original. The images describe what i need.

The ball has a radius which will intersect with the line if it is plotted from the center of the ball.

How can I implement this?