//图片按比例缩放
var flag=false;
function DrawImage(ImgD,iwidth,iheight){
    //参数(图片,允许的宽度,允许的高度)
     var image=new Image();
     image.src=ImgD.src;
    if(image.width>0 && image.height>0){
     flag=true;
    if(image.width/image.height>= iwidth/iheight){
        if(image.width>iwidth){  
         ImgD.width=iwidth;
         ImgD.height=(image.height*iwidth)/image.width;
         }else{
         ImgD.width=image.width;  
         ImgD.height=image.height;
         }
         ImgD.alt=image.width+"×"+image.height;
         }
    else{
        if(image.height>iheight){  
         ImgD.height=iheight;
         ImgD.width=(image.width*iheight)/image.height;        
         }else{
         ImgD.width=image.width;  
         ImgD.height=image.height;
         }
         ImgD.alt=image.width+"×"+image.height;
         }
     }
} 
