利用js加载本地图片预览功能

直接上代码：
经测试，除safari6包括6以下不支持，其他均可正常显示。
原因：safari6不支持filereader，同时不能使用IE滤镜导致失效。
fix: 可以利用canvas，解决safari6的问题
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >

<head>    
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />    
<title>图片上传本地预览</title>    
<style type="text/css">
#preview{width:260px;height:190px;border:1px solid #000;overflow:hidden;}
#imghead {filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>
<script type="text/javascript">

        //图片上传预览    IE是用了滤镜。
        function previewImage(file)
        {
          var MAXWIDTH  = 260;
          var MAXHEIGHT = 180;
          var div = document.getElementById('preview');
          if (file.files && file.files[0])
          {
              div.innerHTML ='<img id=imghead>';
              var img = document.getElementById('imghead');
              img.onload = function(){
                var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
                img.width  =  rect.width;
                img.height =  rect.height;
//                 img.style.marginLeft = rect.left+'px';
                img.style.marginTop = rect.top+'px';
              }
              var reader = new FileReader();
              reader.onload = function(evt){img.src = evt.target.result;}
              reader.readAsDataURL(file.files[0]);
          }
          else //兼容IE
          {
            var sFilter='filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
            file.select();
            var src = document.selection.createRange().text;
            div.innerHTML = '<img id=imghead>';
            var img = document.getElementById('imghead');
            img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = src;
            var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
            status =('rect:'+rect.top+','+rect.left+','+rect.width+','+rect.height);
            div.innerHTML = "<div id=divhead style='width:"+rect.width+"px;height:"+rect.height+"px;margin-top:"+rect.top+"px;"+sFilter+src+"\"'></div>";
          }
        }
        function clacImgZoomParam( maxWidth, maxHeight, width, height ){
            var param = {top:0, left:0, width:width, height:height};
            if( width>maxWidth || height>maxHeight )
            {
                rateWidth = width / maxWidth;
                rateHeight = height / maxHeight;

                if( rateWidth > rateHeight )
                {
                    param.width =  maxWidth;
                    param.height = Math.round(height / rateWidth);
                }else
                {
                    param.width = Math.round(width / rateHeight);
                    param.height = maxHeight;
                }
            }

            param.left = Math.round((maxWidth - param.width) / 2);
            param.top = Math.round((maxHeight - param.height) / 2);
            return param;
        }
</script>    
</head>    
<body>
<div id="preview">
    <img id="imghead" width=100 height=100 border=0 src=''>
</div>

    <input type="file" onchange="previewImage(this)" />    
</body>    
</html>
barbabravo / blog

利用js加载本地图片预览功能 #21
