anchor.diff:     * Horizontal speed of the tiles
      */
     int vx = 0;
  -  
  +
     /**
      * Vertical speed of the tiles.
      */
  
positive.code:       case REPEAT_NONE:
          break;
        case REPEAT_X:
          xTimes = (_context.game.stage.sourceWidth /
              backgroundTileBitmapdata.width).ceil();
          break;
        case REPEAT_Y:
          yTimes = (_context.game.stage.sourceHeight /
              backgroundTileBitmapdata.height).ceil();
          break;
        case REPEAT_XY:
          yTimes = (_context.game.stage.sourceHeight /
              backgroundTileBitmapdata.height).ceil();
          xTimes = (_context.game.stage.sourceWidth /
              backgroundTileBitmapdata.width).ceil();
          break;
      }
      
      
      double xScale = 1.0;
      double yScale = 1.0;
      
      switch (scaleMode) {
        case SCALE_NONE:
          break;
        case SCALE_FULL_X:
          xTimes = 1;
          xScale = (_context.game.stage.sourceWidth / 
              backgroundTileBitmapdata.width);
          break;
        case SCALE_FULL_Y:
          yTimes = 1;
          yScale = (_context.game.stage.sourceHeight /
              backgroundTileBitmapdata.height);
          break;
        case SCALE_FULL_XY:
          xScale = (_context.game.stage.sourceWidth / 
                      backgroundTileBitmapdata.width);
          yScale = (_context.game.stage.sourceHeight /
                      backgroundTileBitmapdata.height);
          break;
      }
  
      for (int i = 0; i < yTimes+1; i++) {
        for (int j = 0; j < xTimes+1; j++) {
          backgroundTileBitmap = new StageXL.Bitmap(backgroundTileBitmapdata);
          backgroundTileBitmap
              ..x = backgroundTileBitmap.width * j
  
negative.code:    * Is the background movable.
     */
    bool isMovable;
  
  
    /**
     * Create tile based background from [worldXL.BitmapData].
     */
    Background.bitmapdata(State stateContext, StageXL.BitmapData bitmapData,
        {bool isMovable: false, bool addToWorld: true, String repeatMode:
        DEFAULT_REPEAT_MODE, String scaleMode: DEFAULT_SCALE_MODE}) {
  
      _context = stateContext;
  
      StageXL.BitmapData backgroundTileBitmapdata = bitmapData;
  