代码描述：
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8"/>
<title> New Document 111111111 </title>
<meta name="Keywords" content="">
<meta name="Description" content="">
<style type="text/css">
#canvas{position:absolute;left:0;top:0;}
</style>
</head>
<body>
<canvas id='canvas' width=800 height=500></canvas>
<script type="text/javascript">
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
canvas.style.backgroundColor='#EEEEFF';
document.onmousemove=move;
function move(e){
}
var arr=[];
var brr=[];
var crr=[];
var drr=[];
var t =null;
canvas.onmousedown = function(e){
var e = e || window.event;
arr.push(e.clientX);
brr.push(e.clientY);
crr.push(400);//起始点x
drr.push(500);//起始点y
//redz(e.clientX,e.clientY);
run();
}
function redz(x,y){
context.save();
context.translate(400,500);
if(x<400){
var deg2 = Math.atan((500-y)/(400 - x))-Math.PI/2;
var dd = context.rotate(deg2);
}else{
var deg2 = Math.atan((500-y)/(400 - x ))+Math.PI/2;
var dd = context.rotate(deg2);
}
context.fillStyle='red';
context.fillRect(0,-50,4,50);
context.restore();
}
redz(200,200);
function run(){
context.clearRect(0,0,canvas.width,canvas.height);
if(t){
clearTimeout(t);
}
circilp();
for (var i=0;i<arr.length ;i++ )
{
redz(arr[arr.length-1],brr[brr.length-1]);
if(arr[i]<400){
crr[i]-=(400 - arr[i])/(500 - brr[i]);
drr[i]-=1;
}else{
crr[i]+=(arr[i] - 400)/(500 - brr[i]);
drr[i]-=1;
}
if(crr[i]<0||crr[i]>800||drr[i]<0){
arr.splice(i,1);
brr.splice(i,1);
crr.splice(i,1);
drr.splice(i,1);
}
context.strokeStyle='blue';
context.strokeRect(crr[i],drr[i],2,2);
}
t = setTimeout(run,2);
}
function circilp(){
context.beginPath();
context.arc(400,530,50,0,Math.PI,true);
context.closePath();
context.fill();
}
circilp();
</script>
</body>
</html>