// Vraci nahodne cislo x, kde 0<=x<num
function randNum (num) {
var rnd1 = Math.round( (num-1) * Math.random() )
    return rnd1;
}

// Snezeni
var items = [ "./images/snow1.gif", "./images/snow2.gif", "./images/snow3.gif" ];
var itemsCount=30;
var screenLeft = 50;
var screenTop = 50;
var screenWidth = screen.availWidth - 150;
var screenHeight = screen.availHeight - 180;
var moveamountY = 10;
var moveamountX = 0;
var randomizeX = 2;
var randomizeY = 3;
var fCycleX = false;
var fCycleY = true;
var fRandomXwhenYCycles = true;
var fRandomYwhenXCycles = false;
var fCycleImages = false;
var speed = 100;


var i;
var Xs = new Array();
var Ys = new Array();
var Is = new Array();

function Animate() {
var y;
    for(i=0; i<itemsCount; i++ ) {

        Ys[i] += moveamountY + ( randNum(2) ? (1) : (-1) ) * randNum(randomizeY);
        Xs[i] += moveamountX + ( randNum(2) ? (1) : (-1) ) * randNum(randomizeX);

        if( Xs[i] > screenLeft + screenWidth )  {
            Xs[i] = fCycleX ? screenLeft : screenLeft + screenWidth;
            Ys[i] = fRandomYwhenXCycles ? screenTop + randNum(screenHeight) : Ys[i];
        }
        if( Ys[i] > screenTop + screenHeight )  {
            Ys[i] = fCycleY ? screenTop : screenTop + screenHeight;
            Xs[i] = fRandomXwhenYCycles ? screenLeft+ randNum(screenWidth) : Xs[i];
        }
        if (fCycleImages) {
            Is[i]++;
            if(Is[i]>=items.length) Is[i]=0;
            document.getElementById('animitem'+i).src = items[ Is[i] ];
        }

        document.getElementById('animitem'+i).style.top = Ys[i];
        document.getElementById('animitem'+i).style.left = Xs[i];
    }
}