Well you can get the current mouse coordinates with mouseX and mouseY; so you just need to check whether these are over your line...  Now, whilst it's not too difficult to test whether the cursor is within the bounds of a rectangle or circle, it's not necessarily all that simple when working with lines since you need to check against the pixel location of every point on the line...

As it happens I remember someone asking this question before and that someone posted a function that solved the problem.

Ok, thank you very much, I think this is the solution to my problem! It is a little hard to understand the "intersection" code, but it's a good challenge for me
Thank you for your help again.