anchor.diff:  
     SnakeState(String n, CanvasRenderingContext2D c) {
       this.name = n;
  -    this.canvas = c;
   
       renderer = new GridRenderer2D(c);
   
  
positive.code: 
      this.direction = randomDirection();
      Coord canvasSize = new Coord(
                          canvas.canvas.width,
                          canvas.canvas.height);
  
      // How many grid blocks will fit into a canvas?
      // Get answer as a coordinate giving number in
  
negative.code: 
    GridRenderer renderer;
  
    static Coord snakePenSizeInPixels = new Coord(640, 480);
    static Coord gridBlockSizeInPixels = new Coord(10, 10);
  
  