// Thanks to Troels Jakobsen <tjak@get2net.dk>
// for fix which makes it work when the page is scrolled
var nDots = 7;
if (document.all&&window.print)
document.body.style.cssText="overflow-x:hidden;overflow-y:scroll"
var Xpos = 0;
var Ypos = 0;
// fixed time step, no relation to real time
var DELTAT = .01;
// size of one spring in pixels
var SEGLEN = 10;
// spring constant, stiffness of springs
var SPRINGK = 10;
// all the physics is bogus, just picked stuff to
// make it look okay
var MASS = 1;
var GRAVITY = 50;
var RESISTANCE = 10;
// stopping criterea to prevent endless jittering
// doesn't work when sitting on bottom since floor
// doesn't push back so acceleration always as big
// as gravity
var STOPVEL = 0.1;
var STOPACC = 0.1;
var DOTSIZE = 11;
// BOUNCE is percent of velocity retained when
// bouncing off a wall
var BOUNCE = 0.75;
var isNetscape = navigator.appName=="Netscape";
// always on for now, could be played with to
// let dots fall to botton, get thrown, etc.
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) {
// I only know how to read the locations of the
// <LI> items in IE
//skip this for now
// setInitPositions(dots)
}
// set their positions
for (i = 0; i < nDots; i++) {
dots[i].obj.left = dots[i].X;
dots[i].obj.top = dots[i].Y;
}
if (isNetscape) {
// start right away since they are positioned
// at 0, 0
startanimate();
} else {
// let dots sit there for a few seconds
// since they're hiding on the real bullets
setTimeout("startanimate()", 2000);
}
}
function startanimate() {
setInterval("animate()", 20);
}
// This is to line up the bullets with actual LI tags on the page
// Had to add -DOTSIZE to X and 2*DOTSIZE to Y for IE 5, not sure why
// Still doesn't work great
function setInitPositions(dots)
{
// initialize dot positions to be on top
// of the bullets in the <ul>
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;
}
// put 0th dot above 1st (it is hidden)
dots[0].X = dots[1].X;
dots[0].Y = dots[1].Y - SEGLEN;
}
// just save mouse position for animate() to use
function MoveHandler(e)
{
Xpos = e.pageX;
Ypos = e.pageY;
return true;
}
// just save mouse position for animate() to use
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;
}
// adds force in X and Y to spring for dot[i] on dot[j]
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() {
// dots[0] follows the mouse,
// though no dot is drawn there
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);
}
// air resisitance/friction
var resist = new vec(-dots[i].dx * RESISTANCE,
-dots[i].dy * RESISTANCE);
// compute new accel, including gravity
var accel = new vec((spring.X + resist.X)/ MASS,
(spring.Y + resist.Y)/ MASS + GRAVITY);
