void setup() {
  size(640,480,P2D);
}

private void branch(float x, float y, float ang, float n, int depthcheck) {
  float dx=(float)Math.cos(ang)*n*mouseY/128;
  float dy=(float)Math.sin(ang)*n*mouseY/128;
  strokeWeight(n/4);
  line(x,y,x+dx,y+dy);
  float dang = PI*n/96;
  if (n>1 && depthcheck>0) {
    branch(x+dx,y+dy,ang+dang+(mouseX-(width>>1))/64f,n*mouseY/512,depthcheck-1);
    branch(x+dx,y+dy,ang-dang+(mouseX-(width>>1))/64f,n*mouseY/512,depthcheck-1);
  }
}

void draw() {
  background(33);
  stroke(99);
  branch(width>>1,height*3>>2,-PI/2,16,8);
}