int planeX, planeY;
int radius;

void setup() {
  size(640, 400);

  planeX = 320;
  planeY = 200;

  radius = 250;
}

void draw() {
  background(150, 150, 220);

  noFill();

  rectMode(CENTER);

  //Kreis um mouse und plane berechnen
  int kreisRadius = getDistance(mouseX, mouseY, planeX, planeY) * 2;
  int kreisMitteX = (mouseX + planeX) / 2;
  int kreisMitteY = (mouseY + planeY) / 2;

  ellipse(kreisMitteX, kreisMitteY, kreisRadius - (kreisRadius / 2), kreisRadius - (kreisRadius / 2));

  ellipse(mouseX, mouseY, radius - (radius/ 2), radius - (radius/ 2));

  //Punkte z1 und z2 berechnen
  int z1x, z1y;
  int z2x, z2y;

  //http://stackoverflow.com/questions/3349125/circle-circle-intersection-points
  int a = (pow(radius, 2) - pow(kreisRadius, 2) - pow(kreisRadius / 2, 2)) / kreisRadius;

  //int p2x = mouseX + a * (mouseX - planeX) / (kreisRadius);
  //int p2y = mouseY + a * (mouseY - planeY) / (kreisRadius);

  p2x = kreisMitteX;
  p2y = kreisMitteY;

  ellipse(p2x, p2y, 10, 10);

  int h = sqrt(pow(radius, 2) + pow(a, 2));

  z1x = p2x + h * (mouseY - planeY) / (kreisRadius / 2);
  z1y = p2y - h * (mouseX - planeX) / (kreisRadius / 2);

  z2x = p2x - h * (mouseY - planeY) / (kreisRadius / 2);
  z2y = p2y + h * (mouseX - planeX) / (kreisRadius / 2);

  ellipse(z1x, z1y, 10, 10);

  ellipse(z2x, z2y, 10, 10);

  fill(255, 255, 255);

  ellipse(mouseX, mouseY, 20, 20);

  rect(planeX,  planeY,  20,  20);
}

int getDistance(int x1, int y1, int x2, int y2) {
  return sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2));
}