Draw an arrow between two circles?

Question

How can I draw an arrowed line between two circles, given:

1. Location of the centers of the cirlces
2. Radius of the circles

I am using

Answer 1

As @andsens said, you're doing a simple vector manipulation.

This can be done much more cleanly if you wrap it in a decent library. For example, I use the nice Sylvester matrix and vector library.

What you're essentially calculating is:

Where v is the vector to the centre of the target, and v_edge the vector to the edge of the target with radius r.

Which you can do easily:

// Assume source and target both have x and y properties
// Assume target has radius property
function path2TargetEdge(source, target){

  // V is the vector from the source to the target's center
  var V = $V([target.x-source.x, target.y-source.y]);

  // Vt is the vector from the source to the edge of the target
  var Vt = V.toUnitVector().multiply(V.modulus() - target.radius);

  return {x: Vt.e(1), y: Vt.e(2) }; // Vectors are 1-indexed
}