解决用H5 Canvas绘制的图片或文字在高清屏下模糊的问题

 var image = new Image();
    image.src=‘../../assets/img/pollution/pollution-province-excellent.png‘;
    image.onload =()=>{
        var canvas = document.createElement(‘canvas‘);
        canvas.width = image.width;
        canvas.height = image.height;
        var ctx = canvas.getContext(‘2d‘);
        ctx.drawImage(image, 0, 0);
        ctx.fillStyle = ‘#fff‘;
        ctx.font=‘14px Arial‘;

        ctx.fillText(‘35‘, 25, 30);
        var image1 = new Image();
        image1.src = canvas.toDataURL();
        var containerNode = document.querySelector(‘#div1‘);
        containerNode.append(canvas);
    };

var image = new Image();
image.src=‘../../assets/img/pollution/pollution-province-excellent.png‘;
image.onload =()=>{
    var canvas = document.createElement(‘canvas‘);
    const {width, height} = image;
    canvas.style.width = width+‘px‘;
    canvas.style.height = height+‘px‘;
    //var scale = window.devicePixelRatio;
    var scale = 2; //我为什么用2，而不用devicePixelRatio数值？因为我的电脑Win10系统设置了自定义缩放比大于devicePixelRatio但小于2（200%）
    canvas.width = Math.floor(width*scale);
    canvas.height = Math.floor(height*scale);
    var ctx = canvas.getContext(‘2d‘);
    ctx.scale(scale, scale);//scale>1表示放大，反之表示缩小。即绘制原先1px现在是绘制scale个pixel
　　 //注意绘制内容在scale之后开始
    ctx.drawImage(image, 0, 0);
    ctx.fillStyle = ‘#ffffff‘;
    ctx.font=‘14px Arial‘;
    ctx.textAlign = ‘center‘;
    ctx.textBaseline = ‘middle‘;
    var x = canvas.width/2;
    var y = canvas.height/2;
    ctx.fillText(‘35‘, x/scale, y/scale);//为什么x/y还除以scale，因为画布实际放大了scale倍，所以x,y绘制的像素也放大了scale，所以再除以scale
    var image1 = new Image();
    image1.src = canvas.toDataURL();
    var containerNode = document.querySelector(‘#div2‘);
    containerNode.append(canvas);
};