跟隨鼠標很逼真的彈性小球

<script language=JavaScript>
var nDots = 7;
var Xpos = 0;
var Ypos = 0;
var DELTAT = .01;
var SEGLEN = 10;
var SPRINGK = 10;
var MASS = 1;
var XGRAVITY = 0;
var YGRAVITY = 50;
var RESISTANCE = 10;
var SVEL = 0.1;
var SACC = 0.1;
var DOTSIZE = 11;
var BOUNCE = 0.75;
var isNetscape = navigator.appName=="Netscape";
var followmouse = true;
var dots = new Array();
init();
function init()
{
var i = 0;
for (i = 0; i < nDots; i ) {
dots[i] = new dot(i);
}

if (!isNetscape) {
}
for (i = 0; i < nDots; i ) {
dots[i].obj.left = dots[i].X;
dots[i].obj.top = dots[i].Y;
}
if (isNetscape) {
startanimate();
} else {
setTimeout("startanimate()", 1000);
}
}
function dot(i)
{
this.X = Xpos;
this.Y = Ypos;
this.dx = 0;
this.dy = 0;
if (isNetscape) {
this.obj = eval("document.dot" i);
} else {
this.obj = eval("dot" i ".style");
}
}
function startanimate() {
setInterval("animate()", 20);
}
function setInitPositions(dots)
{
var startloc = document.all.tags("LI");
var i = 0;
for (i = 0; i < startloc.length && i < (nDots - 1); i ) {
dots[i 1].X = startloc[i].offsetLeft
startloc[i].offsetParent.offsetLeft - DOTSIZE;
dots[i 1].Y = startloc[i].offsetTop
startloc[i].offsetParent.offsetTop 2*DOTSIZE;
}
dots[0].X = dots[1].X;
dots[0].Y = dots[1].Y - SEGLEN;
}
function MoveHandler(e)
{
Xpos = e.pageX;
Ypos = e.pageY;
return true;
}
function MoveHandlerIE() {
Xpos = window.event.x document.body.scrollLeft;
Ypos = window.event.y document.body.scrollTop;
}

if (isNetscape) {
document.captureEvents(Event.MOUSEMOVE);
document.onMouseMove = MoveHandler;
} else {
document.onmousemove = MoveHandlerIE;
}

function vec(X, Y)
{
this.X = X;
this.Y = Y;
}
function springForce(i, j, spring)
{
var dx = (dots[i].X - dots[j].X);
var dy = (dots[i].Y - dots[j].Y);
var len = Math.sqrt(dx*dx dy*dy);
if (len > SEGLEN) {
var springF = SPRINGK * (len - SEGLEN);
spring.X = (dx / len) * springF;
spring.Y = (dy / len) * springF;
}
}
function animate() {
var start = 0;
if (followmouse) {
dots[0].X = Xpos;
dots[0].Y = Ypos;
start = 1;
}
for (i = start ; i < nDots; i ) {

var spring = new vec(0, 0);
if (i > 0) {
springForce(i-1, i, spring);
}
if (i < (nDots - 1)) {
springForce(i 1, i, spring);
}
var resist = new vec(-dots[i].dx * RESISTANCE,
-dots[i].dy * RESISTANCE);
var accel = new vec((spring.X resist.X)/MASS XGRAVITY,
(spring.Y resist.Y)/ MASS YGRAVITY);
dots[i].dx = (DELTAT * accel.X);
dots[i].dy = (DELTAT * accel.Y);
if (Math.abs(dots[i].dx) < SVEL &&
Math.abs(dots[i].dy)< SVEL &&
Math.abs(accel.X)< SACC &&
Math.abs(accel.Y)< SACC) {
dots[i].dx = 0;
dots[i].dy = 0;
}
dots[i].X = dots[i].dx;
dots[i].Y = dots[i].dy;
var height, width;
if (isNetscape) {
height = window.innerHeight window.pageYOffset;
width = window.innerWidth window.pageXOffset;
} else {
height = document.body.clientHeight document.body.scrollTop;
width = document.body.clientWidth document.body.scrollLeft;
}
if (dots[i].Y >= height - DOTSIZE - 1) {
if (dots[i].dy > 0) {
dots[i].dy = BOUNCE * -dots[i].dy;
}
dots[i].Y = height - DOTSIZE - 1;
}
if (dots[i].X >= width - DOTSIZE) {
if (dots[i].dx > 0) {
dots[i].dx = BOUNCE * -dots[i].dx;
}
dots[i].X = width - DOTSIZE - 1;
}
if (dots[i].X < 0) {
if (dots[i].dx < 0) {
dots[i].dx = BOUNCE * -dots[i].dx;
}
dots[i].X = 0;
}
dots[i].obj.left = dots[i].X;
dots[i].obj.top = dots[i].Y;
}
}
</script>

位律師廻複