canvans 翻转翻转
<!DOCTYPE html>
<html>
<body>
<p>要使用的图像：</p>
<img id="tulip" src="http://www.w3school.com.cn/i/eg_tulip.jpg" alt="The Tulip" />
<p>翻转</p>
<canvas id="myCanvas" width="400" height="266" style="border:1px solid #d3d3d3;background:#ffffff;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var img=document.getElementById("tulip");
//垂直
ctx.translate(0, 300);
ctx.scale(1, -1);
ctx.drawImage(img,0,34);
//水平
//ctx.translate(400, 0);
//ctx.scale(-1, 1);
//ctx.drawImage(img,0,0);
</script>
</body>
</html>
https://blog.oldj.net/2011/02/09/flip-images-in-html5/
