code: function(x, y, isSmooth) {
                  //顶点
                  this.vertex = new ShapePoint(x, y);
                  //控制点
                  this.forward = new ShapePoint(x, y);
                  this.backward = new ShapePoint(x, y);
                  //是否平滑
                  this.setSmooth(isSmooth === undefined || isSmooth);
                  this.setSymReflaction(true);
              }
docs: @constructor
  @for kity.BezierPoint
  
  @description 创建一个具有默认顶点坐标的贝塞尔点，两个控制点的坐标和顶点一致
  
  @param  {Number}  x        顶点的 x 坐标
  @param  {Number}  y        顶点的 y 坐标
  @param  {Boolean} isSmooth 指示当前贝塞尔点是否光滑，光滑会约束顶点和两个控制点共线