本程序用于实现动画效果，沿着sin函数画圆，圆心沿着sin函数移动，半径以圆的1/4周期为一个周期周期变化。-This procedure used to achieve animation effects, along the sin function drawcircle, center of a circle along the sin function to move to a radius of a circle 1/4 cycle for a cycle cycle.