sclass SimpleOutlineWalker {
  IIntIntPred pixelIsInside;
  int x, y;
  NEWSDirection direction;
  
  // x, y must be inside the shape
  *(IIntIntPred *pixelIsInside, int *x, int *y) {
    if (!pixelIsInside.get(x, y))
      fail("pixel is not inside shape: " + x + "/" + y);
  }
  
  
}