Fireworks Effect

// <![CDATA[

var bits=100; // numero di fuochi

var intensity=9; // potenza dell’esplosione (da 3 a 10 è meglio)

var speed=15; // velocità - numero più piccolo maggiore velocità

var colours=new Array("#03f", "#f03", "#0e0", "#93f", "#0cc", "#f93");

// blu rosso verde viola ciano arancio
// I codici possono anche essere formati da 6 numeri esadecimali invece che tre

/****************************

* Fireworks Effect *

* http://www.mf2fm.com/rv *

* DON'T EDIT BELOW THIS BOX *

****************************/

var dx, xpos, ypos, bangheight;

var Xpos=new Array();

var Ypos=new Array();

var dX=new Array();

var dY=new Array();

var decay=new Array();

var colour=0;

var swide=800;

var shigh=600;

function write_fire() {

var b, s;

b=document.createElement("div");

s=b.style;

s.position="absolute";

b.setAttribute("id", "bod");

document.body.appendChild(b);

set_scroll();

set_width();

b.appendChild(div("lg", 3, 4));

b.appendChild(div("tg", 2, 3));

for (var i=0; i<bits; i++) b.appendChild(div("bg"+i, 1, 1));

}

function div(id, w, h) {

var d=document.createElement("div");

d.style.position="absolute";

d.style.overflow="hidden";

d.style.width=w+"px";

d.style.height=h+"px";

d.setAttribute("id", id);

return (d);

}

function bang() {

var i, X, Y, Z, A=0;

for (i=0; i<bits; i++) {

X=Math.round(Xpos[i]);

Y=Math.round(Ypos[i]);

Z=document.getElementById("bg"+i).style;

if((X>=0)&&(X<swide)&&(Y>=0)&&(Y<shigh)) {

Z.left=X+"px";

Z.top=Y+"px";

}

if ((decay[i]-=1)>14) {

Z.width="3px";

Z.height="3px";

}

else if (decay[i]>7) {

Z.width="2px";

Z.height="2px";

}

else if (decay[i]>3) {

Z.width="1px";

Z.height="1px";

}

else if (++A) Z.visibility="hidden";

Xpos[i]+=dX[i];

Ypos[i]+=(dY[i]+=1.25/intensity);

}

if (A!=bits) setTimeout("bang()", speed);

}

function stepthrough() {

var i, Z;

var oldx=xpos;

var oldy=ypos;

xpos+=dx;

ypos-=4;

if (ypos<bangheight||xpos<0||xpos>=swide||ypos>=shigh) {

for (i=0; i<bits; i++) {

Xpos[i]=xpos;

Ypos[i]=ypos;

dY[i]=(Math.random()-0.5)*intensity;

dX[i]=(Math.random()-0.5)*(intensity-Math.abs(dY[i]))*1.25;

decay[i]=Math.floor((Math.random()*16)+16);

Z=document.getElementById("bg"+i).style;

Z.backgroundColor=colours[colour];

Z.visibility="visible";

}

bang();

launch();

}

document.getElementById("lg").style.left=xpos+"px";

document.getElementById("lg").style.top=ypos+"px";

document.getElementById("tg").style.left=oldx+"px";

document.getElementById("tg").style.top=oldy+"px";

}

function launch() {

colour=Math.floor(Math.random()*colours.length);

xpos=Math.round((0.5+Math.random())*swide*0.5);

ypos=shigh-5;

dx=(Math.random()-0.5)*4;

bangheight=Math.round((0.5+Math.random())*shigh*0.4);

document.getElementById("lg").style.backgroundColor=colours[colour];

document.getElementById("tg").style.backgroundColor=colours[colour];

}

window.onscroll=set_scroll;

function set_scroll() {

var sleft, sdown;

if (typeof(self.pageYOffset)=="number") {

sdown=self.pageYOffset;

sleft=self.pageXOffset;

}

else if (document.body.scrollTop || document.body.scrollLeft) {

sdown=document.body.scrollTop;

sleft=document.body.scrollLeft;

}

else if (document.documentElement && (document.documentElement.scrollTop || document.documentElement.scrollLeft)) {

sleft=document.documentElement.scrollLeft;

sdown=document.documentElement.scrollTop;

}

else {

sdown=0;

sleft=0;

}

var s=document.getElementById("bod").style;

s.top=sdown+"px";

s.left=sleft+"px";

}

window.onresize=set_width;

function set_width() {

if (typeof(self.innerWidth)=="number") {

swide=self.innerWidth;

shigh=self.innerHeight;

}

else if (document.documentElement && document.documentElement.clientWidth) {

swide=document.documentElement.clientWidth;

shigh=document.documentElement.clientHeight;

}

else if (document.body.clientWidth) {

swide=document.body.clientWidth;

shigh=document.body.clientHeight;

}

window.onload=function() { if (document.getElementById) {

set_width();

write_fire();

launch();

setInterval('stepthrough()', speed);

}}

// ]]>

</script>