### 代码
```
var canvas2 = document.createElement("canvas");
var _canvas = document.getElementById('app');
var w = parseInt(window.getComputedStyle(_canvas).width);
var h = parseInt(window.getComputedStyle(_canvas).height);
//将canvas画布放大若干倍，然后盛放在较小的容器内，就显得不模糊了
var times = 3;
canvas2.width = w * times  * window.devicePixelRatio;
canvas2.height = h * times  * window.devicePixelRatio;
canvas2.style.width = w + "px";
canvas2.style.height =h + "px";
var context = canvas2.getContext("2d");
context.scale(times, times);
console.log(canvas2.style.width)
    new html2canvas(document.getElementById('app'), {
        canvas:canvas2,
        allowTaint: true,
        taintTest: true,
        useCORS: true,
        background: null,
        windowWidth:document.body.scrollWidth,
        windowHeight:document.body.scrollHeight,
        x:0,
        y:0
    }).then(canvas => {
	//canvas就是绘制完成的画板对象
    });
    }
})
```
html2canvas与canvas参考文档
### 重点介绍
context.scale(x 倍数, y 倍数); //这个是画板放大指定倍数
canvas2.width = w * times  * window.devicePixelRatio; //指定画板宽度
canvas2.height = h * times  * window.devicePixelRatio; //指定画板宽度
为什么要再乘以window.devicePixelRatio这个其实是设备的dip，canvas设置的宽度是像素 但是页面的单位是px 1px = 1dip 这样就会让页面超出canvas 让截图出现放大 并且显示不完全。
这就是原因，也是卡了两天的bug。