/*
   实现页面图片的等比缩小,同时遵循宽度优先的原则
   obj_id :要改变元素的ID
   obj_width :要求改变以后的宽度
   obj_height :要求改变以后的高度
   author : Peter_Zhang
   date : 2007-10-14
*/

function chang_Img_display(obj_id,obj_width,obj_height){
     var var_img_width = obj_width;
	 var var_img_height = obj_height;
	 var last_img_width;
	 var last_img_height;
     var obj = document.getElementById(obj_id);
	 //only width big
	 if(obj.width > var_img_width && obj.height <= var_img_height){
		 last_img_height = obj.height * (var_img_width / obj.width);
		 if(last_img_height > var_img_height){
			obj.height = var_img_height;
		 }else{
		    obj.width = var_img_width;
		 }
	 //only height big
	 }else if(obj.height > var_img_height && obj.width <= var_img_width){
	     last_img_width = obj.width * (var_img_height / obj.height);
		 if(last_img_width > var_img_width){
		      obj.width = var_img_width;
		 }else{
		      obj.height = var_img_height;
		 }
	 //all big
	 }else if(obj.width > var_img_width && obj.height > var_img_height){
	    var WIDTH_BL = obj.width / var_img_width;
		var HEIGHT_BL = obj.height / var_img_height;

		if(WIDTH_BL > HEIGHT_BL){
		   obj.width = var_img_width;
		}else{
		   obj.height = var_img_height;
		}
	 }
}