Connect two circles with a line

Question

I\'m drawing two shapes (circles) in a JPanel and I need to connect them with a line. I was doing this by just getting the middle point of the circle and connecting each oth

Answer 1

My trick:

Let the two centers be C0 and C1. Using complex numbers, you map these two points to a horizontal segment from the origin by the transformation

P' = (P - C0) (C1 - C0)* / L

where * denotes conjugation and L = |C1 - C0|. (If you don't like the complex number notation, you can express this with matrices as well.)

Now the visible part of the segment goes from (R0, 0) to (L - R1, 0). The two other vertices of the arrow are at (L - R1 - H, W) and (L - R1 - H, -W) for an arrowhead of height H and width 2W.

By applying the inverse transform you get the original coordinates,

P = C0 + L P' / (C1 - C0)*.