等比例缩放边框函数

等比例缩放边框：

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){    
      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;    
          }    
      }else{    
          if(image.height>iheight){      
              ImgD.height=iheight;    
              ImgD.width=(image.width*iheight)/image.height;            
          }else{    
              ImgD.width=image.width;      
              ImgD.height=image.height;    
          }    
      }    
    }    
}