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>