anchor.diff:    }
   
     void clearCanvas() {
  -    var gc = canvas.canvas.getContext('2d');
  -    canvas.fillStyle = white_color;
  -    canvas.fillRect(0, 0, gridBlockSizeInPixels.getX(), gridBlockSizeInPixels.getY());
  +    fillCanvas(white_color);
     }
   
     void renderGridBlock(final Coord c, final String color) {
  
positive.code: class GridRenderer2D {
    CanvasRenderingContext2D canvas;
  
    String gold_color = "#FFD700";
     String white_color = "#FFFFFF";
  
    static Coord snakePenSizeInPixels = new Coord(640, 480);
    static Coord gridBlockSizeInPixels = new Coord(10, 10);
  
negative.code:     canvas.fillRect(gridBlockSizeInPixels.getX() * c.getX(),
          gridBlockSizeInPixels.getY() * c.getY(), gridBlockSizeInPixels.getX(),
          gridBlockSizeInPixels.getY());
    }
  
    void fillCanvas(String color) {
      canvas.fillStyle = color;
      canvas.fillRect(0, 0, snakePenSizeInPixels.getX(),
      snakePenSizeInPixels.getY());
    }
  }
  
  