srecord noeq BresenhamLineDrawer(int x1, int y1, int x2, int y2) is Iterable<Pt> {
  int mainStepX, mainStepY;
  int sideStepX, sideStepY;
  int i, steps;
  int x, y;
  int fraction, increment;
  
  simplyCached void init {
    x = x1; y = y1;
    if (x2-x1 > y2-y1) {
      // go mainly horizontal (right or left)
      mainStepX = sideStepX = sign(x2-x1);
      sideStepY = sign(y2-y1);
      steps = abs(x2-x1);
      increment = abs(y2-y1);
    } else {
      // go mainly vertical (up or down)
      mainStepY = sideStepY = sign(y2-y1);
      sideStepX = sign(x2-x1);
      steps = abs(y2-y1);
      increment = abs(x2-x1);
    }
  }
  
  Pt next() {
    init();
    if (i > steps) null;
    
    Pt p = pt(x1, y1);
    if (++i < steps) {
      fraction += increment;
      if (fraction >= steps) {
        fraction -= steps;
        x += sideStepX;
        y += sideStepY;
      } else {
        x += mainStepX;
        y += mainStepY;
      }
    }
    
    ret p;
  }
  
  public ItIt<Pt> iterator() { ret iff_null(-> next()); }
}