如何实现图片的无缝循环滚动

解决思路：
一个设定宽度并且隐藏超出它宽度的内容的容器demo，里面放demo1和demo2，demo1是滚动内容,demo2为demo1的直接克隆副本，通过不断改变demo1的scrollTop或者scrollLeft达到滚动的目的，当滚动至demo1与demo2的交界处时直接跳回初始位置，因为demo1与demo2一样，所以分不出跳动的瞬间，从而达到"无缝"滚动的目的。

具体步骤：
1.向上滚动。

<base href=http://www.cnwebshow.com>
<div id=demo style=overflow:hidden;height:100;width:90;
background:#214984;color:#ffffff>
<div id=demo1>
<img src="images/webshow.gif">
<img src="images/link/flashempire.gif">
<img src="images/linklogo/shlogo.gif">
<img src="images/link/deskcity.gif">
<img src="images/linklogo/5dmeng.gif">
<img src="http://www.blueidea.com/logo.gif";>
<img src="images/link/flashskylogo.gif">
<img src="images/link/5dlogo88.gif">
<img src="http://www.webshow.com/cgercn/link.gif";>
</div>
<div id=demo2></div>
</div>
<script>
var speed=30
demo2.innerHTML=demo1.innerHTML //克隆demo1为demo2
function Marquee(){
//当滚动至demo1与demo2交界时
if(demo2.offsetTop-demo.scrollTop<=0)
demo.scrollTop-=demo1.offsetHeight //demo跳到最顶端
else{
demo.scrollTop++
}
}
var MyMar=setInterval(Marquee,speed)//设置定时器
//鼠标移上时清除定时器达到滚动停止的目的
demo.onmouseover=function() {clearInterval(MyMar)}
//鼠标移开时重设定时器
demo.onmouseout=function(){MyMar=setInterval(Marquee,speed)}
</script>


2.向下滚动。

<base href=http://www.cnwebshow.com>
<div id=demo style=overflow:hidden;height:100;width:90;
background:#214984;color:#ffffff>
<div id=demo1>
<img src="images/flash8.gif">
<img src="images/link/flashempire.gif">
<img src="images/linklogo/shlogo.gif">
<img src="images/link/deskcity.gif">
<img src="images/linklogo/5dmeng.gif">
<img src="http://www.blueidea.com/logo.gif";>
<img src="images/link/flashskylogo.gif">
<img src="images/link/5dlogo88.gif">
<img src="http://www.yiiboo.com/cgercn/link.gif";>
</div>
<div id=demo2></div>
</div>
<script>
var speed=30
demo2.innerHTML=demo1.innerHTML
demo.scrollTop=demo.scrollHeight
function Marquee(){
if(demo1.offsetTop-demo.scrollTop>=0)
demo.scrollTop+=demo2.offsetHeight
else{
demo.scrollTop--
}
}
var MyMar=setInterval(Marquee,speed)
demo.onmouseover=function() {clearInterval(MyMar)}
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)}
</script>


3.向左滚动。

<base href=http://www.cnwebshow.com>
<div id=demo style=overflow:hidden;height:33;width:500;
background:#214984;color:#ffffff>
<table align=left cellpadding=0 cellspace=0 border=0>
<tr>
<td id=demo1 valign=top>
<img src="images/link/flashempire.gif">
<img src="images/linklogo/shlogo.gif">
<img src="images/link/deskcity.gif">
<img src="images/linklogo/5dmeng.gif">
<img src="http://www.blueidea.com/logo.gif";>
<img src="images/link/flashskylogo.gif">
<img src="images/link/5dlogo88.gif">
<img src="http://www.yiiboo.com/cgercn/link.gif";>
<img src="images/flash8.gif">
</td>
<td id=demo2 valign=top></td>
</tr>
</table>
</div>
<script>
var speed=30
demo2.innerHTML=demo1.innerHTML
function Marquee(){
if(demo2.offsetWidth-demo.scrollLeft<=0)
demo.scrollLeft-=demo1.offsetWidth
else{
demo.scrollLeft++
}
}
var MyMar=setInterval(Marquee,speed)
demo.onmouseover=function() {clearInterval(MyMar)}
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)}
</script>


4.向右滚动。

<base href=http://www.cnwebshow.com>
<div id=demo style=overflow:hidden;height:33;width:500;
background:#214984;color:#ffffff>
<table align=left cellpadding=0 cellspace=0 border=0>
<tr>
<td id=demo1 valign=top>
<img src="images/link/flashempire.gif">
<img src="images/linklogo/shlogo.gif">
<img src="images/link/deskcity.gif">
<img src="images/linklogo/5dmeng.gif">
<img src="http://www.blueidea.com/logo.gif";>
<img src="images/link/flashskylogo.gif">
<img src="images/link/5dlogo88.gif">
<img src="http://www.yiiboo.com/cgercn/link.gif";>
<img src="images/flash8.gif">
</td>
<td id=demo2 valign=top></td>
</tr>
</table>
</div>
<script>
var speed=30
demo2.innerHTML=demo1.innerHTML
demo.scrollLeft=demo.scrollWidth
function Marquee(){
if(demo.scrollLeft<=0)
demo.scrollLeft+=demo2.offsetWidth
else{
demo.scrollLeft--
}
}
var MyMar=setInterval(Marquee,speed)
demo.onmouseover=function() {clearInterval(MyMar)}
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)}
</script>

提示：关于循环滚动的原理，光看本例代码的话可能会觉得枯涩难懂，那样的话可以运行下面修改过的代码，注意滚动条和背景颜色的变化：

<base href=http://www.cnwebshow.com>
<div id=demo>
<img src="images/webshow.gif">
<img src="images/link/flashempire.gif">
<img src="images/linklogo/shlogo.gif">
<img src="images/link/deskcity.gif">
<img src="images/linklogo/5dmeng.gif">
<img src="http://www.blueidea.com/logo.gif";>
<img src="images/link/flashskylogo.gif">
<img src="images/link/5dlogo88.gif">
</div>
<script>
function Marquee(obj,speed){
with(obj){
innerHTML=["<div>","</div><div style=’background:green’>","</div>"].join(innerHTML)
onmouseover=function(){clearInterval(MyMar)}
onmouseout=function(){
MyMar=setInterval(function(){
with(obj)
scrollTop+=(scrollTop<=lastChild.offsetTop?1:-lastChild.offsetHeight)},speed)}
fireEvent("onmouseout")
}
}
Marquee(demo,30)
</script>

特别提示
运行本例所给的四段代码，将看到图片分别按指定的上、下、左和右四个方向循环滚动。图1.8.29为提示中所给代码的运行效果，可以看到，Y轴的滚动滑块滚动一段距离(在红色背景的那块滚动到顶端时)后又自动跳到顶端。