可绘制bizier curve, 无控制点数量限制,可用鼠标右键改变控制点位置,从而改变bizier curve的表现.双击鼠标左键可结束绘制.同时也可通过右侧指令修改或结束图像绘制.-to draw bizier curve, no limit of the number of the control points. and you can also change the position of the control points by using the right button of t