var Imgvalue;
var Count =13;   //圖片數量
var Imgs = new Array(Count);
var ImgLoaded =0;
//預加載圖片
function preLoadImgs()
{
alert('圖片加載中請稍等......');
for(var i=0;i<Imgs.length;i++){
Imgs[i]=new Image();
downloadImage(i);
}
}
//加載單個圖片
function downloadImage(i)
{
    var imageIndex = i+1; //圖片以1開始
    Imgs[i].src = "images/"+imageIndex+".jpg";
    Imgs[i].onLoad=validateImages(i);
}
//驗證是否成功加載完成，如不成功則重新加載
function validateImages(i){
if (!Imgs[i].complete)
    {
     window.setTimeout('downloadImage('+i+')',200);    
    }
else if (typeof Imgs[i].naturalWidth != "undefined" && Imgs[i].naturalWidth == 0)
    {
    window.setTimeout('downloadImage('+i+')',200);
    }
    else 
    {
        ImgLoaded++
        if(ImgLoaded == Count)
        {
            document.getElementById('BtnStart').disabled=false;
            document.getElementById('BtnStop').disabled=false;
            alert('圖片加載完畢！');
        }
    }
}
//開始
function RandStart()
{
    Init = setInterval('SetRand()',50);    
}
//隨機顯示
function SetRand()
{
    imageIndex = Math.floor(Math.random()*Count);
    document.getElementById("ImgView").src = Imgs[imageIndex].src;
}
//結束
function RandStop()
{
    window.clearInterval(Init);
}