AutoScroller

/**//*
 * Copyright (C) 2007-2009 skylark
 * Email:aohailin@gmail.com
 * Version:2.1
 * 原创程序,转载请保留版权
 */
var $=function(o){return typeof o=="string"?document.getElementById(o):o;};
function AutoScroll(){
    this.obj=[];
    this.version="2.1";
    this.Build();//初始化
};
AutoScroll.prototype.Build=function(){
    var me=this;
    //取得其他滚动事件
    var oldscroll=window.onscroll;
    window.onscroll=function(){
        //保护其他滚动事件
        if("function"==typeof oldscroll){
            oldscroll();
        }
        //得到客户端浏览器参数,兼容IE，FF，Chrome
        this.common={
            t:document.documentElement.scrollTop||document.body.scrollTop,
            h:document.documentElement.clientHeight||document.body.clientHeight,
            w:document.documentElement.clientWidth||document.body.clientWidth
        };
        this.position=[];
        for(var i=0;i<me.obj.length;i++){
            try{
                this.style={};
                //获得客户端位置,设置了7种位置
                //为了让最小化自动适应位置,这里动态计算位置,所以滚动事件触发时,CPU消耗很大
                this.position[i]=[
                    {x:0,y:this.common.t},
                    {x:this.common.w-me.obj[i].obj.offsetWidth,y:this.common.t},
                    {x:0,y:(this.common.h+this.common.t-me.obj[i].obj.offsetHeight)/2+(this.common.t)/2},
                    {x:this.common.w-me.obj[i].obj.offsetWidth,y:(this.common.h+this.common.t-me.obj[i].obj.offsetHeight)/2+(this.common.t)/2},
                    {x:(this.common.w-me.obj[i].obj.offsetWidth)/2,y:(this.common.h+this.common.t-me.obj[i].obj.offsetHeight)/2+(this.common.t)/2},
                    {x:0,y:this.common.h+this.common.t-me.obj[i].obj.offsetHeight},
                    {x:this.common.w-me.obj[i].obj.offsetWidth,y:this.common.h+this.common.t-me.obj[i].obj.offsetHeight}
                ];
                //处理自定义样式
                this.style="object"==typeof me.obj[i].style?{x:me.obj[i].style.left,y:me.obj[i].style.top+this.common.t}:{x:this.position[i][me.obj[i].style].x,y:this.position[i][me.obj[i].style].y};
                //定位
                me.obj[i].obj.style.left=this.style.x+"px";
                me.obj[i].obj.style.top=this.style.y+"px";            
            }catch(e){            
                //功能是过滤无效obj
                for(var j=i;j<me.obj.length-1;j++){
                    me.obj[j]=me.obj[j+1];
                    me.obj.length=me.obj.length-1;
                }
            }
        }
    };
    //初始化
    window.scroll(1,1);
};
AutoScroll.prototype.Add=function(){
    var obj=arguments[0];
    //获得当前position
    var oldposition=$(obj.id).style.position;
    $(obj.id).style.position="absolute";
    //不使用fixed,虽然高版本浏览器都已经支持fixed
    this.obj.push({
        obj:$(obj.id),
        oldposition:oldposition,
        style:obj.style
     });
};
AutoScroll.prototype.Remove=function(){
    var obj=arguments[0];
    for(var i=0;i<this.obj.length;i++){
        if(this.obj[i].obj==$(obj.id)){
            //还原初始状态position
            this.obj[i].obj.style.position=this.obj[i].oldposition;
            //是否真正移除
            if(obj.remove){
                this.obj[i].obj.innerHTML="";
                document.body.removeChild(this.obj[i].obj);
            }
            //移除obj
            for(var j=i;j<this.obj.length-1;j++){
                this.obj[j]=this.obj[j+1];
            }
            this.obj.length=this.obj.length-1;
            break;
        }
    }
};
var Scroller=new AutoScroll();