docs: function (rect) {
          if (rect) {
              this.context.clearRect(rect.origin.x, rect.origin.y, rect.size.width, rect.size.height)
          } else {
              this.canvas.width = this.canvas.width
              if (cc.FLIP_Y_AXIS) {
                  this.context.scale(1, -1)
                  this.context.translate(0, -this.canvas.height)
              }
          }
      }