Inserire effetto neve di Natale sul forum

<script type="text/javascript">
var snowStorm = null;

function SnowStorm() {

 this.flakesMax = 128;
 this.flakesMaxActive = 32;
 this.animationInterval = 20;
 this.flakeBottom = null;
 this.targetElement = null;
 this.followMouse = true;
 this.snowColor = '#fff';
 this.snowCharacter = '•';
 this.snowStick = true;
 this.useMeltEffect = true;
 this.useTwinkleEffect = false;
 this.usePositionFixed = false;
 // --- settings added to acp at later date ---
 this.flakeLeftOffset = 0;       // amount to subtract from edges of container
 this.flakeRightOffset = 0;      // amount to subtract from edges of container
 this.flakeWidth = 12;            // max pixel width for snow element
 this.flakeHeight = 12;           // max pixel height for snow element
 this.vMaxX = 5;                 // Maximum X velocity range for snow
 this.vMaxY = 4;                 // Maximum Y velocity range
 this.zIndex = 0;                // CSS stacking order applied to each snowflake
 // --- settings added to acp at later date ---
 var addEvent = (typeof(window.attachEvent)=='undefined'?function(o,evtName,evtHandler) {
       return o.addEventListener(evtName,evtHandler,false);
 }:function(o,evtName,evtHandler) {
       return o.attachEvent('on'+evtName,evtHandler);
 });
 var removeEvent = (typeof(window.attachEvent)=='undefined'?function(o,evtName,evtHandler) {
   return o.removeEventListener(evtName,evtHandler,false);
 }:function(o,evtName,evtHandler) {
       return o.detachEvent('on'+evtName,evtHandler);
 });
 function rnd(n,min) {
   if (isNaN(min)) {
         min = 0;
       }
   return (Math.random()*n)+min;
 }
 function plusMinus(n) {
   return (parseInt(rnd(2),10)==1?n*-1:n);
 }
 var s = this;
 var storm = this;
 this.timers = [];
 this.flakes = [];
 this.disabled = false;
 this.active = false;
 var isIE = navigator.userAgent.match(/msie/i);
 var isIE6 = navigator.userAgent.match(/msie 6/i);
 var isOldIE = (isIE && (isIE6 || navigator.userAgent.match(/msie 5/i)));
 var isWin9X = navigator.appVersion.match(/windows 98/i);
 var isiPhone = navigator.userAgent.match(/iphone/i);
 var isBackCompatIE = (isIE && document.compatMode == 'BackCompat');
 var noFixed = ((isBackCompatIE || isIE6 || isiPhone)?true:false);
 var screenX = null;
 var screenX2 = null;
 var screenY = null;
 var scrollY = null;
 var vRndX = null;
 var vRndY = null;
 var windOffset = 1;
 var windMultiplier = 2;
 var flakeTypes = 6;
 var fixedForEverything = false;
 var opacitySupported = (function(){
   try {
         document.createElement('div').style.opacity = '0.5';
   } catch (e) {
         return false;
   }
   return true;
 })();
 var docFrag = document.createDocumentFragment();
 if (s.flakeLeftOffset === null) {
       s.flakeLeftOffset = 0;
 }
 if (s.flakeRightOffset === null) {
       s.flakeRightOffset = 0;
 }
 this.meltFrameCount = 20;
 this.meltFrames = [];
 for (var i=0; i<this.meltFrameCount; i++) {
       this.meltFrames.push(1-(i/this.meltFrameCount));
 }
 this.randomizeWind = function() {
   vRndX = plusMinus(rnd(s.vMaxX,0.2));
   vRndY = rnd(s.vMaxY,0.2);
   if (this.flakes) {
     for (var i=0; i<this.flakes.length; i++) {
       if (this.flakes[i].active) {
         this.flakes[i].setVelocities();
               }
     }
   }
 };
 this.scrollHandler = function() {
   scrollY = (s.flakeBottom?0:parseInt(window.scrollY||document.documentElement.scrollTop||document.body.scrollTop,10));
   if (isNaN(scrollY)) {
         scrollY = 0; // Netscape 6 scroll fix
       }
   if (!fixedForEverything && !s.flakeBottom && s.flakes) {
     for (var i=s.flakes.length; i--;) {
       if (s.flakes[i].active === 0) {
             s.flakes[i].stick();
               }
     }
   }
 };
 this.resizeHandler = function() {
   if (window.innerWidth || window.innerHeight) {
     screenX = window.innerWidth-(!isIE?16:2)-s.flakeRightOffset;
     screenY = (s.flakeBottom?s.flakeBottom:window.innerHeight);
   } else {
     screenX = (document.documentElement.clientWidth||document.body.clientWidth||document.body.scrollWidth)-(!isIE?8:0)-s.flakeRightOffset;
     screenY = s.flakeBottom?s.flakeBottom:(document.documentElement.clientHeight||document.body.clientHeight||document.body.scrollHeight);
   }
   screenX2 = parseInt(screenX/2,10);
 };
 this.resizeHandlerAlt = function() {
   screenX = s.targetElement.offsetLeft+s.targetElement.offsetWidth-s.flakeRightOffset;
   screenY = s.flakeBottom?s.flakeBottom:s.targetElement.offsetTop+s.targetElement.offsetHeight;
   screenX2 = parseInt(screenX/2,10);
 };
 this.freeze = function() {
   // pause animation
   if (!s.disabled) {
     s.disabled = 1;
   } else {
     return false;
   }
   for (var i=s.timers.length; i--;) {
     clearInterval(s.timers[i]);
   }
 };
 this.resume = function() {
   if (s.disabled) {
      s.disabled = 0;
   } else {
     return false;
   }
   s.timerInit();
 };
 this.toggleSnow = function() {
   if (!s.flakes.length) {
     // first run
     s.start();
   } else {
     s.active = !s.active;
     if (s.active) {
       s.show();
       s.resume();
     } else {
       s.stop();
       s.freeze();
     }
   }
 };
 this.stop = function() {
   this.freeze();
   for (var i=this.flakes.length; i--;) {
     this.flakes[i].o.style.display = 'none';
   }
   removeEvent(window,'scroll',s.scrollHandler);
   removeEvent(window,'resize',s.resizeHandler);
   if (!isOldIE) {
     removeEvent(window,'blur',s.freeze);
     removeEvent(window,'focus',s.resume);
   }
 };
 this.show = function() {
   for (var i=this.flakes.length; i--;) {
     this.flakes[i].o.style.display = 'block';
   }
 };
 this.SnowFlake = function(parent,type,x,y) {
   var s = this;
   var storm = parent;
   this.type = type;
   this.x = x||parseInt(rnd(screenX-20),10);
   this.y = (!isNaN(y)?y:-rnd(screenY)-12);
   this.vX = null;
   this.vY = null;
   this.vAmpTypes = [1,1.2,1.4,1.6,1.8]; // "amplification" for vX/vY (based on flake size/type)
   this.vAmp = this.vAmpTypes[this.type];
   this.melting = false;
   this.meltFrameCount = storm.meltFrameCount;
   this.meltFrames = storm.meltFrames;
   this.meltFrame = 0;
   this.twinkleFrame = 0;
   this.active = 1;
   this.fontSize = (10+(this.type/5)*10);
   this.o = document.createElement('div');
   this.o.innerHTML = storm.snowCharacter;
   this.o.style.color = storm.snowColor;
   this.o.style.position = (fixedForEverything?'fixed':'absolute');
   this.o.style.width = storm.flakeWidth+'px';
   this.o.style.height = storm.flakeHeight+'px';
   this.o.style.fontFamily = 'arial,verdana';
   this.o.style.overflow = 'hidden';
   this.o.style.fontWeight = 'normal';
   this.o.style.zIndex = storm.zIndex;
   docFrag.appendChild(this.o);
   this.refresh = function() {
         if (isNaN(s.x) || isNaN(s.y)) {
               // safety check
               return false;
         }
     s.o.style.left = s.x+'px';
     s.o.style.top = s.y+'px';
   };
   this.stick = function() {
     if (noFixed || (storm.targetElement != document.documentElement && storm.targetElement != document.body)) {
       s.o.style.top = (screenY+scrollY-storm.flakeHeight)+'px';
     } else if (storm.flakeBottom) {
           s.o.style.top = storm.flakeBottom+'px';
         } else {
       s.o.style.display = 'none';
           s.o.style.top = 'auto';
       s.o.style.bottom = '0px';
           s.o.style.position = 'fixed';
       s.o.style.display = 'block';
     }
   };
   this.vCheck = function() {
     if (s.vX>=0 && s.vX<0.2) {
       s.vX = 0.2;
     } else if (s.vX<0 && s.vX>-0.2) {
       s.vX = -0.2;
     }
     if (s.vY>=0 && s.vY<0.2) {
       s.vY = 0.2;
     }
   };
   this.move = function() {
     var vX = s.vX*windOffset;
     s.x += vX;
     s.y += (s.vY*s.vAmp);
     if (s.x >= screenX || screenX-s.x < storm.flakeWidth) { // X-axis scroll check
       s.x = 0;
     } else if (vX < 0 && s.x-storm.flakeLeftOffset<0-storm.flakeWidth) {
       s.x = screenX-storm.flakeWidth-1; // flakeWidth;
     }
     s.refresh();
     var yDiff = screenY+scrollY-s.y;
     if (yDiff<storm.flakeHeight) {
       s.active = 0;
           if (storm.snowStick) {
         s.stick();
           } else {
             s.recycle();
           }
     } else {
           if (storm.useMeltEffect && s.active && s.type < 3 && !s.melting && Math.random()>0.998) {
             // ~1/1000 chance of melting mid-air, with each frame
             s.melting = true;
             s.melt();
             // only incrementally melt one frame
             // s.melting = false;
           }
           if (storm.useTwinkleEffect) {
                 if (!s.twinkleFrame) {
                       if (Math.random()>0.9) {
                     s.twinkleFrame = parseInt(Math.random()*20,10);
                   }
                 } else {
                       s.twinkleFrame--;
                       s.o.style.visibility = (s.twinkleFrame && s.twinkleFrame%2===0?'hidden':'visible');
                 }
           }
     }
   };
   this.animate = function() {
     s.move();
   };
   this.setVelocities = function() {
     s.vX = vRndX+rnd(storm.vMaxX*0.12,0.1);
     s.vY = vRndY+rnd(storm.vMaxY*0.12,0.1);
   };
       this.setOpacity = function(o,opacity) {
         if (!opacitySupported) {
               return false;
         }
         o.style.opacity = opacity;
       };
   this.melt = function() {
         if (!storm.useMeltEffect || !s.melting) {
               s.recycle();
         } else {
               if (s.meltFrame < s.meltFrameCount) {
                 s.meltFrame++;
                 s.setOpacity(s.o,s.meltFrames[s.meltFrame]);
                 s.o.style.fontSize = s.fontSize-(s.fontSize*(s.meltFrame/s.meltFrameCount))+'px';
                 s.o.style.lineHeight = storm.flakeHeight+2+(storm.flakeHeight*0.75*(s.meltFrame/s.meltFrameCount))+'px';
               } else {
                 s.recycle();
               }
         }
   };
   this.recycle = function() {
     s.o.style.display = 'none';
     s.o.style.position = (fixedForEverything?'fixed':'absolute');
     s.o.style.bottom = 'auto';
     s.setVelocities();
     s.vCheck();
         s.meltFrame = 0;
         s.melting = false;
         s.setOpacity(s.o,1);
         s.o.style.padding = '0px';
         s.o.style.margin = '0px';
         s.o.style.fontSize = s.fontSize+'px';
         s.o.style.lineHeight = (storm.flakeHeight+2)+'px';
         s.o.style.textAlign = 'center';
         s.o.style.verticalAlign = 'baseline';
     s.x = parseInt(rnd(screenX-storm.flakeWidth-20),10);
     s.y = parseInt(rnd(screenY)*-1,10)-storm.flakeHeight;
     s.refresh();
     s.o.style.display = 'block';
     s.active = 1;
   };
   this.recycle(); // set up x/y coords etc.
   this.refresh();
 };
 this.snow = function() {
   var active = 0;
   var used = 0;
   var waiting = 0;
   var flake = null;
   for (var i=s.flakes.length; i--;) {
     if (s.flakes[i].active == 1) {
       s.flakes[i].move();
       active++;
     } else if (s.flakes[i].active === 0) {
       used++;
     } else {
       waiting++;
     }
     if (s.flakes[i].melting) {
           s.flakes[i].melt();
         }
   }
   if (active<s.flakesMaxActive) {
     flake = s.flakes[parseInt(rnd(s.flakes.length),10)];
     if (flake.active === 0) {
       flake.melting = true;
     }
   }
 };
 this.mouseMove = function(e) {
   if (!s.followMouse) {
         return true;
       }
   var x = parseInt(e.clientX,10);
   if (x<screenX2) {
     windOffset = -windMultiplier+(x/screenX2*windMultiplier);
   } else {
     x -= screenX2;
     windOffset = (x/screenX2)*windMultiplier;
   }
 };
 this.createSnow = function(limit,allowInactive) {
   for (var i=0; i<limit; i++) {
     s.flakes[s.flakes.length] = new s.SnowFlake(s,parseInt(rnd(flakeTypes),10));
     if (allowInactive || i>s.flakesMaxActive) {
           s.flakes[s.flakes.length-1].active = -1;
         }
   }
   storm.targetElement.appendChild(docFrag);
 };
 this.timerInit = function() {
   s.timers = (!isWin9X?[setInterval(s.snow,s.animationInterval)]:[setInterval(s.snow,s.animationInterval*3),setInterval(s.snow,s.animationInterval)]);
 };
 this.init = function() {
   s.randomizeWind();
   s.createSnow(s.flakesMax); // create initial batch
   addEvent(window,'resize',s.resizeHandler);
   addEvent(window,'scroll',s.scrollHandler);
   if (!isOldIE) {
     addEvent(window,'blur',s.freeze);
     addEvent(window,'focus',s.resume);
   }
   s.resizeHandler();
   s.scrollHandler();
   if (s.followMouse) {
     addEvent(document,'mousemove',s.mouseMove);
   }
   s.animationInterval = Math.max(20,s.animationInterval);
   s.timerInit();
 };
 var didInit = false;
 this.start = function(bFromOnLoad) {
       if (!didInit) {
         didInit = true;
       } else if (bFromOnLoad) {
         // already loaded and running
         return true;
       }
   if (typeof s.targetElement == 'string') {
         var targetID = s.targetElement;
     s.targetElement = document.getElementById(targetID);
     if (!s.targetElement) {
           throw new Error('Snowstorm: Unable to get targetElement "'+targetID+'"');
         }
   }
       if (!s.targetElement) {
         s.targetElement = (!isIE?(document.documentElement?document.documentElement:document.body):document.body);
       }
   if (s.targetElement != document.documentElement && s.targetElement != document.body) {
         s.resizeHandler = s.resizeHandlerAlt; // re-map handler to get element instead of screen dimensions
       }
   s.resizeHandler(); // get bounding box elements
   s.usePositionFixed = (s.usePositionFixed && !noFixed); // whether or not position:fixed is supported
   fixedForEverything = s.usePositionFixed;
   if (screenX && screenY && !s.disabled) {
     s.init();
     s.active = true;
   }
 };
 function doStart() {
         s.start(true);
 }
 if (document.addEventListener) {
   // safari 3.0.4 doesn't do DOMContentLoaded, maybe others - use a fallback to be safe.
   document.addEventListener('DOMContentLoaded',doStart,false);
   window.addEventListener('load',doStart,false);
 } else {
   addEvent(window,'load',doStart);
 }
}
snowStorm = new SnowStorm();
</script>