js实现图片加载特效（从左到右，百叶窗，从中间到两边）

/*
　　网上百度的，感觉”从中间到两边“的效果写的不是很好，改了一下，感觉可以了！
*/
<html>
  <head>
    <title></title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <script type="text/javascript">
        var image;
        var intervalId1;
        var intervalId2;
        var intervalId3;
        var drawW1 = 0;
        var canvas;
        var context;
        var drawLeft;
 
        var baiyechuangItemW ;
        function init(){
            image = new Image();
            image.src="eg_mouse.jpg";
            canvas = document.getElementById("canvas1");
            context = canvas.getContext("2d");
            drawLeft = image.width/2;
        }
         
        function startLeftToRight(){
            clearInterval(intervalId1);
            context.clearRect(0,0,image.width,image.height);
            intervalId1 = setInterval("leftToRight();",50);
        }
         
        function leftToRight(){
            context.drawImage(image,0,0,drawW1, image.height,0,0,drawW1,image.height);
            drawW1 += 2;
            if(drawW1>image.width){
                drawW1 =0;
                clearInterval(intervalId1);
            }
        }
          
        function centerToOuter(){
            drawW1 += 2;
　　　　　　　//drawLeft-drawW1/2是左端点，drawLeft是中间， drawLeft+drawW1/2是右端点
            context.drawImage(image,drawLeft-drawW1/2,0,drawW1,image.height,drawLeft-drawW1/2,0,drawW1,image.height);
            if(drawW1>drawLeft*2){
                drawW1 = 0;
                clearInterval(intervalId2);
            }
        }
         
        function startCenterToOuter(){
            clearInterval(intervalId2);
            context.clearRect(0,0,image.width,image.height);
            intervalId2 = setInterval("centerToOuter();",50);
        }
 
        function baiyechuang(){
            for(i=0;i<10;i++){
                context.drawImage(image,baiyechuangItemW*i,0,drawW1,image.height,baiyechuangItemW*i,0,drawW1,image.height);
            }
            drawW1 += 0.2;
            if(drawW1>baiyechuangItemW){
                clearInterval(intervalId3);
            }
        }
         
        function startBaiyechuang(){
            drawW1=0;
            baiyechuangItemW = image.width/10.0;
            clearInterval(intervalId3);
            context.clearRect(0,0,image.width,image.height);
            intervalId3 = setInterval("baiyechuang();", 50);
        }
         
    </script>
  </head>
  <body onload="init();">
      <h1><input type="button" value="从左到右装载图片"  onclick="startLeftToRight();"/></h1>
      <h1><input type="button" value=“从中间到两边加载图片"  onclick="startCenterToOuter();"/></h1>
      <h1><input type="button" value="百叶窗方式装载图片"  onclick="startBaiyechuang();"/></h1>
       
      <div>
          <canvas id="canvas1" width="400px" height="400px"></canvas>
      </div>
  </body>
</html>