int byo = 0;
void setup() {
  size(600, 600);
  frameRate(0.5);
}
void draw(){
 background(255); 
  dragon(200, 140, 450, 500, byo);
  byo ++;
  if(byo > 18){
    byo = 0;
  }
}
void dragon(float x1, float y1, float x2, float y2, int n) {
  if (n > 0) {
    float ang = angle(x1, y1, x2, y2);
    float d = dist(x1, y1, x2, y2);
    float mx = (x1 + x2) / 2.0 + d / 2 * cos(ang + PI/2);
    float my = (y1 + y2) / 2.0 + d / 2 * sin(ang + PI/2);
    if (n == 1) {
      line(x1, y1, mx, my);
      line(x2, y2, mx, my);
    }
    else {
      dragon(x1, y1, mx, my, n-1);
      dragon(x2, y2, mx, my, n-1);
    }
  }else{
   line(x1, y1, x2, y2);
  }
}
float angle(float x1, float y1, float x2, float y2) {
  float angle = 0.0;
  if (x1 == x2) {
    if (y1 < y2)  return PI/2.0;
    if (y1 > y2)  return -PI/2.0;
    if (y1 == y2)  return 0.0;
  }
  angle = atan((y2-y1)/(x2-x1));
  if (x1 > x2)  angle -= PI;
  if (angle < 0.0)  angle += PI*2.0;
  if (angle > PI*2.0)  angle -= PI*2.0;
  return angle;
}