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Пример скрипта: нитка с шариками

Скрипт показывает эффект эластичного перемещения небольших картинок по экрану. В данном примере, в качестве картинок используются небольшие шарики, изображающие привязанную к курсору эластичную нить.



Исходный код этого примера:

<div id="dot0" style="position: absolute; visibility: hidden; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>
<div id="dot1" style="position: absolute; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>
<div id="dot2" style="position: absolute; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>
<div id="dot3" style="position: absolute; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>
<div id="dot4" style="position: absolute; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>
<div id="dot5" style="position: absolute; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>
<div id="dot6" style="position: absolute; height: 11;
      width: 11;"><img src="bullet.gif" height=11 width=11></div>

<script type="text/javascript">
<!--
var nDots = 7;
var Xpos = 0;
var Ypos = 0;

var DELTAT = .01;
var SEGLEN = 10;
var SPRINGK = 10;
var MASS = 1;
var GRAVITY = 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) {
// I only know how to read the locations of the
// <LI> items in IE
//skip this for now
// setInitPositions(dots)
}
for (i = 0; i < nDots; i++) {
	dots[i].obj.left = dots[i].X;
	dots[i].obj.top = dots[i].Y;
}
if (isNetscape) {
	startanimate();
} else {
// let dots sit there for a few seconds
// since they're hiding on the real bullets
setTimeout("startanimate()", 3000);
   }
}

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;
}

// 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() {
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, (spring.Y + resist.Y) / MASS + GRAVITY);
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 + document.scrollTop;
	width = window.innerWidth + document.scrollLeft;
} 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>



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