背景に画像がひらひらと落下する

ＪＡＶＡを使って画面上に画像をひらひらと落下させる（複数画像が指定できる）
<SCRIPT language="JavaScript1.2">
<!-- Begin
//<!-- Original: Altan (snow@altan.hr) -->
//<!-- Web Site: http://www.altan.hr/snow -->
var no = 10; // １画面に出る画像の枚数
var speed = 10; // smaller number moves the STAR faster　ここはあまり替わらないようです
STAR = new Array();
STAR[0] = "1.gif"; 　　　　// 画像の指定。STAR[?]の数字は0から始まる
STAR[1] = "2.gif"; 　　　　// 「""」の中に落下させる画像を指定する
STAR[2] = "3.gif"; 　　　  //　出来れば同じフォルダー内に、画像は何個でも可
STAR[3] = "4.gif";　　　　 //　行頭に「//」が有ると表示（JAVAを動かなくする命令）しない
//STAR[4] = "5.gif";

var ns4up = (document.layers) ? 1 : 0; // browser sniffer
var ie4up = (document.all) ? 1 : 0;
var dx, xp, yp; // coordinate and position variables
var am, stx, sty; // amplitude and step variables
var i, doc_width = 800, doc_height = 800;　  //落下する画面のサイズ

if (ns4up) {
doc_width = self.innerWidth;
doc_height = self.innerHeight;
} else if (ie4up) {
doc_width = document.body.clientWidth;
doc_height = document.body.clientHeight;
}

dx = new Array();
xp = new Array();
yp = new Array();
am = new Array();
stx = new Array();
sty = new Array();
j = 0;

for (i = 0; i < no; ++ i) {
dx[i] = 0; // set coordinate variables
xp[i] = Math.random()*(doc_width-50); // set position variables
yp[i] = Math.random()*doc_height;
am[i] = Math.random()*20; // set amplitude variables
stx[i] = 0.02 + Math.random()/10; // set step variables
sty[i] = 0.7 + Math.random(); // set step variables
if (ns4up) { // set layers
if (i == 0) {
document.write("<layer name=\"dot"+ i +"\" left=\"15\" top=\"15\" visibility=\"show\"><img src=\"" + STAR[j] + "\" border=\"0\"></layer>");
} else {
document.write("<layer name=\"dot"+ i +"\" left=\"15\" top=\"15\" visibility=\"show\"><img src=\"" + STAR[j] + "\" border=\"0\"></layer>");
}
} else if (ie4up) {
if (i == 0) {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: absolute; Z-INDEX: "+ i +" VISIBILITY: visible; TOP: 15px; LEFT: 15px; width:1;\"><img src=\"" + STAR[j] + "\" border=\"0\"></div>");
} else {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: absolute; Z-INDEX: "+ i +" VISIBILITY: visible; TOP: 15px; LEFT: 15px; width:1;\"><img src=\"" + STAR[j] + "\" border=\"0\"></div>");
}
}
if (j == (STAR.length-1)) { j = 0; } else { j += 1; }
}

function STAR_NS() { // Netscape main animation function
for (i = 0; i < no; ++ i) { // iterate for every dot
yp[i] += sty[i];
if (yp[i] > doc_height-50) {
xp[i] = Math.random()*(doc_width-am[i]-30);
yp[i] = 0;
stx[i] = 0.02 + Math.random()/10;
sty[i] = 0.7 + Math.random();
doc_width = self.innerWidth;
doc_height = self.innerHeight;
}
dx[i] += stx[i];
document.layers["dot"+i].top = yp[i];
document.layers["dot"+i].left = xp[i] + am[i]*Math.sin(dx[i]);
}
setTimeout("STAR_NS()", speed);
}

function STAR_IE() { // IE main animation function
for (i = 0; i < no; ++ i) { // iterate for every dot
yp[i] += sty[i];
if (yp[i] > doc_height-50) {
xp[i] = Math.random()*(doc_width-am[i]-30);
yp[i] = 0;
stx[i] = 0.02 + Math.random()/10;
sty[i] = 0.7 + Math.random();
doc_width = document.body.clientWidth;
doc_height = document.body.clientHeight;
}
dx[i] += stx[i];
document.all["dot"+i].style.pixelTop = yp[i];
document.all["dot"+i].style.pixelLeft = xp[i] + am[i]*Math.sin(dx[i]);
}
setTimeout("STAR_IE()", speed);
}

if (ns4up) {
STAR_NS();
} else if (ie4up) {
STAR_IE();
}

// End -->
</SCRIPT>