JavaScript实现的贝塞尔曲线算法简单示例

<div style="position:absolute;left:0;top:0;width:500px;height:300px;overflow:hidden;"><svg id="root" width="500" height="300" viewBox="0 0 500 300" xmlns="http://www.w3.org/2000/svg"><title>svg</title><path d="M20,100 c80 -200 280 200 380 0 h-400" fill="none" stroke-width="1" stroke="gray" stroke-dasharray="3,3" /></svg></div><div id="dotMove" style="position:absolute;width:6px;height:6px;overflow:hidden;background-color:#FF0000;"></div><script type="text/javascript">/*参考维基百科http://zh.wikipedia.org/wiki/%E8%B2%9D%E8%8C%B2%E6%9B%B2%E7%B7%9A*/function Point2D(x,y){  this.x=x||0.0;  this.y=y||0.0;}/* cp在此是四元素的列: cp[0]起始，或上中的P0 cp[1]第一控制，或上中的P1 cp[2]第二控制，或上中的P2 cp[3]束，或上中的P3 t值，0 <= t <= 1*/function PointOnCubicBezier( cp, t ){  var  ax, bx, cx;  var  ay, by, cy;  var  tSquared, tCubed;  var  result = new Point2D ;  /*算多式*/  cx = 3.0 * (cp[1].x - cp[0].x);  bx = 3.0 * (cp[2].x - cp[1].x) - cx;  ax = cp[3].x - cp[0].x - cx - bx;  cy = 3.0 * (cp[1].y - cp[0].y);  by = 3.0 * (cp[2].y - cp[1].y) - cy;  ay = cp[3].y - cp[0].y - cy - by;  /*算位於值t的曲*/  tSquared = t * t;  tCubed = tSquared * t;  result.x = (ax * tCubed) + (bx * tSquared) + (cx * t) + cp[0].x;  result.y = (ay * tCubed) + (by * tSquared) + (cy * t) + cp[0].y;  return result;}/* ComputeBezier以控制cp所生的曲，填入Point2D的列。 呼叫者必分配足的以供出果，其<sizeof(Point2D) numberOfPoints>*/function ComputeBezier( cp, numberOfPoints, curve ){  var  dt;  var  i;  dt = 1.0 / ( numberOfPoints - 1 );  for( i = 0; i < numberOfPoints; i++)    curve[i] = PointOnCubicBezier( cp, i*dt );}var cp=[  new Point2D(20, 0), new Point2D(100, 200), new Point2D(300, -200), new Point2D(400, 0)];var numberOfPoints=100;var curve=[];ComputeBezier( cp, numberOfPoints, curve );var i=0, dot=document.getElementById("dotMove");setInterval(function (){  var j = (i<100)?i:(199-i);  dot.style.left=curve[j].x+'px';  dot.style.top=100-curve[j].y+'px';  if(++i==200)i=0;}, 50);</script>