3 points and circle

gistfile1.txt

// calcuate center point from given three points
// http://paulbourke.net/geometry/circlesphere/
PVector calculateCenter(PVector p1, PVector p2, PVector p3) {
  float ma = (p2.y - p1.y) / (p2.x - p1.x);
  float mb = (p3.y - p2.y) / (p3.x - p2.x);
  float x = (ma * mb * (p1.y - p3.y) + mb * (p1.x + p2.x) - ma * (p2.x + p3.x)) / ( 2 * (mb - ma));
  float y = (p1.x - p3.x + ma * (p1.y + p2.y) - mb * (p2.y + p3.y)) / (2 * (ma - mb));
  return new PVector(x, y);
}