跟隨鼠標很逼真的彈性小球

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<DIV id=dot0
style="HEIGHT: 16; POSITION: absolute; VISIBILITY: hidden; WIDTH: 11; left:10; top:15"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<DIV id=dot1 style="HEIGHT: 11px; POSITION: absolute; WIDTH: 11px"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<DIV id=dot2 style="HEIGHT: 11px; POSITION: absolute; WIDTH: 11px"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<DIV id=dot3 style="HEIGHT: 11px; POSITION: absolute; WIDTH: 11px"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<DIV id=dot4 style="HEIGHT: 11px; POSITION: absolute; WIDTH: 11px"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<DIV id=dot5 style="HEIGHT: 11px; POSITION: absolute; WIDTH: 11px"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<DIV id=dot6 style="HEIGHT: 16; POSITION: absolute; WIDTH: 11; left:10; top:15"><IMG
height=11 src="images/201302/1359861949038686149.gif" width=11> </DIV>
<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 STOPVEL = 0.1;
var STOPACC = 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) < STOPVEL &&
            Math.abs(dots[i].dy) < STOPVEL &&
            Math.abs(accel.X) < STOPACC &&
            Math.abs(accel.Y) < STOPACC) {
            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>