案例：html/html5 案例     状态：可编辑再运行    进入竖版
 运行结果　
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<!DOCTYPE html>
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<html>
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<body>
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​
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<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
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Your browser does not support the HTML5 canvas tag.
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</canvas>
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​
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<script>
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​
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var c=document.getElementById("myCanvas");
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var ctx=c.getContext("2d");
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ctx.fillStyle="green";
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ctx.fillRect(10,10,50,50);
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​
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var imgData=ctx.getImageData(30,30,50,50);
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red=imgData.data[0];
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green=imgData.data[1];
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blue=imgData.data[2];
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alpha=imgData.data[3];
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alert(red + " " + green + " " + blue + " " + alpha);
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​
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</script>
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​
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</body>
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</html>
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​