code: function (x, y, width, height) {
              this.backBufferContext2D.clearRect(x, y, width, height);
          }
docs: Erase the pixels in the given rectangular area by setting them to transparent black (rgba(0,0,0,0)).
  @name clearRect
  @memberOf me.CanvasRenderer.prototype
  @function
  @param {Number} x x axis of the coordinate for the rectangle starting point.
  @param {Number} y y axis of the coordinate for the rectangle starting point.
  @param {Number} width The rectangle's width.
  @param {Number} height The rectangle's height.