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很棒的JavaScript!!(彈性)

http://infoserv.com.tw Pinus (2001-06-03 10:08:00)

<BODY bgColor=#ffffff> 
<DIV><BR></DIV> 
<DIV> </DIV> 
<DIV id=dot0 
style="VISIBILITY: hidden; WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<DIV id=dot1 style="WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<DIV id=dot2 style="WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<DIV id=dot3 style="WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<DIV id=dot4 style="WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<DIV id=dot5 style="WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<DIV id=dot6 style="WIDTH: 11px; POSITION: absolute; HEIGHT: 11px"><IMG 
height=11 src="bullet.gif" width=11></DIV> 
<SCRIPT language=JavaScript> 
<!-- hide code

/* 
Elastic Trail script (By Philip Winston @ pwinston@yahoo.com, URL:http://members.xoom.com/ebullets) 
Script featured on Dynamicdrive.com 
For this and 100's more DHTML scripts, visit http://dynamicdrive.com 
*/

// 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 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); 
}

// 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);

// compute new velocity 
dots[i].dx += (DELTAT * accel.X); 
dots[i].dy += (DELTAT * accel.Y);

// stop dead so it doesn't jitter when nearly still 
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; 
}

// move to new position 
dots[i].X += dots[i].dx; 
dots[i].Y += dots[i].dy;

// get size of window 
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; 
}

// bounce of 3 walls (leave ceiling open) 
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; 
}

// move img to new position 
dots[i].obj.left = dots[i].X; 
dots[i].obj.top = dots[i].Y; 
} 
}

// end code hiding --> 
</SCRIPT> 
</BODY>

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