The_snowfall

adds falling snowflakes to the page
Este script no debería instalarse directamente. Es una biblioteca que utilizan otros scripts mediante la meta-directiva de inclusión // @require https://update.greasyfork.org/scripts/513921/1470984/The_snowfall.js
Pregunta tus dudas, ponle nota o notifica una posible infracción de las normas.
Ajuste de línea
// Add this script before </body> tag, 
// its must be pasted in the last pair of tags <script></script>

// CREDITS:
// Snowmaker
// By Peter Gehrig
// Copyright (c) 2003 Peter Gehrig. All rights reserved.
// Permission given to use the script provided that this notice remains as is.
// Additional scripts can be found at http://www.24fun.com
// [email protected]
// 11/27/2003

// IMPORTANT:
// If you add this script to a script-library or script-archive
// you have to add a highly visible link to
// http://www.24fun.com on the webpage
// where this script will be featured

///////////////////////////////////////////////////////////////////////////
// CONFIGURATION STARTS HERE
///////////////////////////////////////////////////////////////////////////

// Set the number of snowflakes (more than 30 - 40 not recommended)
var snowmax=35;

// Set the colors for the snow. Add as many colors as you like
var snowcolor=new Array("#aaaacc","#ddddFF","#ccccDD");

// Set the fonts, that create the snowflakes. Add as many fonts as you like
var snowtype=new Array("Arial Black","Arial Narrow","Times","Comic Sans MS");

// Set the letter that creates your snowflake (recommended:*)
var snowletter="*";

// Set the speed of sinking (recommended values range from 0.3 to 2)
var sinkspeed=0.6;

// Set the maximal-size of your snowflaxes
var snowmaxsize=22;

// Set the minimal-size of your snowflaxes
var snowminsize=13;

// Set the snowing-zone
// Set 1 for all-over-snowing, set 2 for left-side-snowing 
// Set 3 for center-snowing, set 4 for right-side-snowing
var snowingzone=1;

///////////////////////////////////////////////////////////////////////////
// CONFIGURATION ENDS HERE
///////////////////////////////////////////////////////////////////////////


// Do not edit below this line
var snow=new Array();
var marginbottom;
var marginright;
var timer;
var i_snow=0;
var x_mv=new Array();
var crds=new Array();
var lftrght=new Array();
var browserinfos=navigator.userAgent;
var ie5=document.all&&document.getElementById&&!browserinfos.match(/Opera/);
var ns6=document.getElementById&&!document.all;
var opera=browserinfos.match(/Opera/);
var browserok=ie5||ns6||opera;

function randommaker(range) {		
	rand=Math.floor(range*Math.random());
    return rand;
}

function initsnow() {
	if (ie5 || opera) {
		marginbottom = document.body.clientHeight;
		marginright = document.body.clientWidth;
	}
	else if (ns6) {
		marginbottom = window.innerHeight;
		marginright = window.innerWidth;
	}
	var snowsizerange=snowmaxsize-snowminsize;
	for (i=0;i<=snowmax;i++) {
		crds[i] = 0;                      
    	lftrght[i] = Math.random()*15;         
    	x_mv[i] = 0.03 + Math.random()/10;
		snow[i]=document.getElementById("s"+i);
		snow[i].style.fontFamily=snowtype[randommaker(snowtype.length)];
		snow[i].size=randommaker(snowsizerange)+snowminsize;
		snow[i].style.fontSize=snow[i].size;
		snow[i].style.color=snowcolor[randommaker(snowcolor.length)];
		snow[i].sink=sinkspeed*snow[i].size/5;
		if (snowingzone==1) {snow[i].posx=randommaker(marginright-snow[i].size);}
		if (snowingzone==2) {snow[i].posx=randommaker(marginright/2-snow[i].size);}
		if (snowingzone==3) {snow[i].posx=randommaker(marginright/2-snow[i].size)+marginright/4;}
		if (snowingzone==4) {snow[i].posx=randommaker(marginright/2-snow[i].size)+marginright/2;}
		snow[i].posy=randommaker(2*marginbottom-marginbottom-2*snow[i].size);
		snow[i].style.left=snow[i].posx;
		snow[i].style.top=snow[i].posy;
	}
	movesnow();
}

function movesnow() {
	for (i=0;i<=snowmax;i++) {
		crds[i] += x_mv[i];
		snow[i].posy+=snow[i].sink;
		snow[i].style.left=snow[i].posx+lftrght[i]*Math.sin(crds[i]);
		snow[i].style.top=snow[i].posy;
		
		if (snow[i].posy>=marginbottom-2*snow[i].size || parseInt(snow[i].style.left)>(marginright-3*lftrght[i])){
			if (snowingzone==1) {snow[i].posx=randommaker(marginright-snow[i].size);}
			if (snowingzone==2) {snow[i].posx=randommaker(marginright/2-snow[i].size);}
			if (snowingzone==3) {snow[i].posx=randommaker(marginright/2-snow[i].size)+marginright/4;}
			if (snowingzone==4) {snow[i].posx=randommaker(marginright/2-snow[i].size)+marginright/2;}
			snow[i].posy=0;
		}
	}
	var timer=setTimeout("movesnow()",50);
}

for (i=0;i<=snowmax;i++) {
	document.write("<span id='s"+i+"' style='position:absolute;top:-"+snowmaxsize+"'>"+snowletter+"</span>");
}
if (browserok) {
	window.onload=initsnow;
}