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srecord noeq BresenhamLineDrawer(int x1, int y1, int x2, int y2) extends Meta 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)+1;
      increment = abs(y2-y1);
    } else {
      // go mainly vertical (up or down)
      mainStepY = sideStepY = sign(y2-y1);
      sideStepX = sign(x2-x1);
      steps = abs(y2-y1)+1;
      increment = abs(x2-x1);
    }
  }
  
  Pt next() {
    init();
    
    if (i >= steps) null;
    
    Pt p = pt(x, y);
    if (++i < steps) {
      fraction += increment;
      if (fraction >= steps) {
        fraction -= steps;
        x += sideStepX;
        y += sideStepY;
      } else {
        x += mainStepX;
        y += mainStepY;
      }
      if (scaffolding())
        printVars(+i, +steps, +fraction, +increment, +steps, +x, +y, +p);
    }
    
    ret p;
  }
  
  public ItIt<Pt> iterator() { ret iff_null(-> next()); }
}