本文實例講述了js實現宇宙星空背景效果的方法。分享給大家供大家參考。具體實現方法如下：
代碼如下:
<!DOCTYPE html PUBLIC "-//W3C//h2D XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/h2D/xhtml1-transitional.h2d">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<TITLE>宇宙星空背景效果，Js特效</TITLE>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
.star {
position:absolute;
layer-background-color:white;
visibility:visible;
top:-50px;
width:50px;
height:50px;
font-size:1px;
background-color:white;
}
.60pt{font-size:60pt;color:#ff66cc;}
</style>
<SCRIPT LANGUAGE="JavaScript">
<!--
var starnum = 75; // 星星的數目
var isNS = (document.layers);
var _all = (isNS)? '' : 'all.';
var _style = (isNS) ? '' : '.style';
var xoffset, yoffset, w_x, w_y, tmpx, tmpy, scrlx, scrly;
function getstartpos(obj) { //定義星星移動的起始位置
obj.deltay = Math.floor(Math.random() * 12); //用隨機函數決定
obj.deltax = Math.floor(Math.random() * 12);
obj.xdir = (Math.floor(Math.random() * 2) == 1) ? '+' : '-';
obj.ydir = (Math.floor(Math.random() * 2) == 1) ? '+' : '-';
obj.counter = 1;
if (isNS) {
obj.clip.width = 1;
obj.clip.height = 1;
obj.moveTo(xoffset+pageXOffset, yoffset+pageYOffset);
} else {
obj.width = 1;
obj.height = 1;
obj.pixelTop = yoffset+document.body.scrollTop;
obj.pixelLeft = xoffset+document.body.scrollLeft;
}
}
function movestar(starN) //移動星星的位置
{
tmpx = starN.deltax*starN.counter+starN.counter;
tmpy = starN.deltay*starN.counter+starN.counter;
if (isNS) {
starN.clip.width = starN.counter / 3;
starN.clip.height = starN.counter / 3;
scrlx = pageXOffset;
scrly = pageYOffset;
if ((starN.left+tmpx >= w_x+scrlx) || (starN.top+tmpy >= w_y+scrly) || (starN.left-tmpx <= scrlx) || (starN.top-tmpy <= scrly)) {
getstartpos(starN);
} else {
eval('starN.moveBy('+starN.xdir+tmpx+', '+starN.ydir+tmpy+')');
}
} else {
starN.width = starN.counter/3;
starN.height = starN.counter/3;
scrlx = document.body.scrollLeft;
scrly = document.body.scrollTop;
if ((starN.pixelLeft+tmpx >= w_x+scrlx)||(starN.pixelTop+tmpy >= w_y+scrly) || (starN.pixelLeft-tmpx <= scrlx)||(starN.pixelTop-tmpy <= scrly)) {
getstartpos(starN);
} else {
eval('starN.pixelTop'+starN.ydir+'=tmpy');
eval('starN.pixelLeft'+starN.xdir+'=tmpx');
}
}
starN.counter++;
}
function animate() //讓所有的星星動起來
{
for(i=1; i <= starnum; i++) {
movestar(eval('star'+i));
}
setTimeout('animate()', 100);
}
function findwindowparams() { //定義星星移動的起始位置
w_x = (isNS) ? window.innerWidth : document.body.clientWidth;
w_y = (isNS) ? window.innerHeight : document.body.clientHeight;
xoffset = w_x / 2;
yoffset = w_y / 2;
for (i = 1; i <= starnum; i++) {
getstartpos(eval('star'+i));
}
}
function resizeNS() {
setTimeout('document.location.reload()', 400);
}
(isNS) ? window.onresize = resizeNS : window.onresize = findwindowparams;
window.onload = new Function("findwindowparams(); animate();");
-->
</script>
</HEAD>
<BODY>
<body bgcolor=#999999>
<SCRIPT LANGUAGE="JavaScript">
<!--
for (i = 1; i <= starnum; i++) { //給星星定義層
document.writeln('<div id="star'+i+'" class="star"></div>');
eval('var star'+i+'=document.'+_all+'star'+i+_style);
}
-->
</script>
<p><center>
<font class=60pt><br>飛翔在<br>宇宙的星空中<br></font>
</center><p>
</body>
</html>
運行效果如下圖所示：
希望本文所述對大家的javascript程序設計有所幫助。