用贝塞尔曲线实现粒子效果。粒子会根据当前画板中绘制的路线进行移动。计入应用后，任意绘制一条曲线，点击开始，会有粒子跟随路径不停的移动-Bezier curve to achieve the effect of the particles. The particles will move in the path of the current drawn Sketchpad. After factoring application, any draw a curve, click Start, wi