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 //
- 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 thevar 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; } }