JavaScript onde sinusoïdale

track : function(x, y, top, ampl) {
        return {
            top : top + 2,
            x   : x + ampl * Math.sin(top / 20),
            y   : (top / this.screenHeight < 0.65) ? y + 2 : 1 + y + ampl * Math.cos(top / 25)
        };
    }

Cette routine envoie des flocons de neige de vol de l'onde sinusoïdale.

Mais comment fait-il? Veuillez expliquer.

Il utilise Math.sin pour x; et Math.cos pour y, mais d'autres extraits que j'ai vu utiliser dans le sens inverse. Pourquoi? Exactement pourquoi top/20 et top/25?

L'ensemble du code:

<script type="text/javascript">
var snowflakes = { //Namespace
/* Settings */
pics : [
['snow.gif' , 24, 24],
['snow2.gif', 24, 24],
['snow3.gif', 24, 24]
],
track : function(x, y, top, ampl) {
return {
top : top + 2,
x   : x + ampl * Math.sin(top / 20),
y   : (top / this.screenHeight < 0.65) ? y + 2 : 1 + y + ampl * Math.cos(top / 25)
};
},
quantity : 30,
minSpeed : 20, //1 - 100, minSpeed <= maxSpeed
maxSpeed : 40, //1 - 100, maxSpeed >= minSpeed
isMelt : true, //true OR false
/* Properties */
screenWidth : 0,
screenHeight : 0,
archive : [],
timer : null,
/* Methods */
addHandler : function(object, event, handler, useCapture) {
if (object.addEventListener) object.addEventListener(event, handler, useCapture);
else if (object.attachEvent)object.attachEvent('on' + event, handler);
else object['on' + event] = handler;
},
create : function(o, index) {
var rand = Math.random();
this.timer = null;
this.o = o;
this.index = index;
this.ampl = 3 + 7*rand;
this.type =  Math.round((o.pics.length - 1) * rand);
this.width = o.pics[this.type][1];
this.height = o.pics[this.type][2];
this.speed = o.minSpeed + (o.maxSpeed - o.minSpeed) * rand;
this.speed = 1000 / this.speed;
this.deviation = o.maxDeviation * rand;
this.x = o.screenWidth * rand - this.width;
this.y = 0 - this.height;
this.top = this.y;
this.img = document.createElement('img');
this.img.src = o.pics[this.type][0];
this.img.style.top = this.y + 'px';
this.img.style.position = 'absolute';
this.img.style.zIndex = 10000;
this.img.style.left = this.x + 'px';
this.img.obj = this;
if (o.isMelt) this.img.onmouseover = function() {
clearTimeout(this.obj.timer);
this.obj.timer = null;
this.parentNode.removeChild(this);
}
document.body.appendChild(this.img);
this.move();
},
init : function() {
this.screenWidth = window.innerWidth ? window.innerWidth : (document.documentElement.clientWidth ? document.documentElement.clientWidth : document.body.offsetWidth);
this.screenWidth = navigator.userAgent.toLowerCase().indexOf('gecko') == -1 ? this.screenWidth : document.body.offsetWidth;
this.screenHeight = window.innerHeight ? window.innerHeight : (document.documentElement.clientHeight ? document.documentElement.clientHeight : document.body.offsetHeight);
this.screenScroll = (window.scrollY) ? window.scrollY : document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop;
this.archive[this.archive.length] = new this.create(this, this.archive.length);
clearTimeout(this.timer);
this.timer = null
this.timer = setTimeout(function(){snowflakes.init()}, 60000 / this.quantity);
}
};
snowflakes.create.prototype = {
move : function() {
var newXY = this.o.track(this.x, this.y, this.top, this.ampl);
this.x   = newXY.x;
this.y   = newXY.y;
this.top = newXY.top;
if (this.y < this.o.screenHeight + this.o.screenScroll - this.height) {
this.img.style.top  = this.y + 'px';
this.x = this.x < this.o.screenWidth - this.width ? this.x : this.o.screenWidth - this.width;
this.img.style.left = this.x + 'px';
var index = this.index;
this.timer = setTimeout(function(){snowflakes.archive[index].move()}, this.speed);
} else {
delete(this.o.archive[this.index]);
this.img.parentNode.removeChild(this.img);
}
}
};
snowflakes.addHandler(window, 'load', function() {snowflakes.init();});
snowflakes.addHandler(window, 'resize', function() {snowflakes.init();});
</script>

OriginalL'auteur DrStrangeLove | 2011-08-26