视网膜显示

Retina和超高分辨率显示器的像素尺寸小于人眼可以分辨的平均尺寸。渲染一条线然后看起来像一条较轻的线。要解决涉及的问题，检测高分辨率显示的页面会将默认的CSS像素大小更改为2。

DOM知道这一点并调整其渲染以进行补偿。但Canvas并不知道，它的渲染只是按比例放大。画布的默认显示渲染类型是双线性插值。这样可以平滑从一个像素到下一个像素的过渡，这对于照片很有用，但对于线条，文本，SVG等来说并不是那么好。

一些解决方案

首先是在画布上转动双线性过滤。这可以通过CSS规则image-rendering: pixelated;来完成。虽然这不会创建在DOM上呈现的SVG的质量，但它会减少一些用户体验到的模糊外观。
将SVG渲染到画布时，应关闭图像平滑，因为这会降低svg图像的质量。 SVG在内部呈现，在内部副本渲染到画布上时不需要额外的平滑。

要执行此操作ctx.imageSmoothingEnabled = false;
检测CSS像素大小。窗口变量devicePixelRatio返回CSS像素的大小与实际屏幕物理像素大小的比较。 Retina和High res设备的值通常为2.然后您可以使用它来设置画布分辨率以匹配物理像素分辨率。

但是存在一个问题，因为所有浏览器都不支持devicePixelRatio，devicePixelRatio受页面缩放设置的影响。

所以最基本的使用devicePixelRatio并假设很少有人放大超过200％。

代码假设canvas.style.width和canvas.style.height已正确设置。

if(devicePixelRatio >= 2){        
    canvas.width *= 2;
    canvas.height *= 2;
}

既然您已经提高了分辨率，那么您还必须增加渲染大小。这可以通过canvas转换完成，更好的是将其创建为函数。

function setCanvasForRetina(canvas){
    canvas.width *= 2;
    canvas.height *= 2;
    canvas.setTransform(2,0,0,2,0,0);
}

注意我不会将像素大小增加＆＃34; devicePixelRatio＆＃34;的值。这是因为视网膜设备的分辨率只有2倍，如果宽高比大于2则是因为客户端已经放大了。为了满足画布的预期行为，如果可以，我不会调整缩放设置。虽然这不是一个规则只是一个建议。

更好的猜猜

上述两种方法可以是停止间隙解决方案，也可以是简单猜测。你可以通过检查一些系统来提高你的几率。

Retina显示器目前采用一组固定的分辨率，适用于固定的设备（手机，平板电脑，笔记本电脑）。

您可以查询window.screen.width和window.screen.height以确定绝对物理像素分辨率，并将其与已知的视网膜显示分辨率进行匹配。您还可以查询userAgent以确定设备类型和品牌。

将所有内容放在一起可以改善猜测。如果显示是视网膜，下一个功能会猜测。如果设备是视网膜，您可以使用类似于确定的东西，然后相应地增加画布分辨率。

wiki Retina Display Models处的以下代码的信息如果您想要保持最新，可以使用Wiki的SPARQL界面查询此信息。

演示猜猜Retina。

＆＃13;

rWidth.textContent = screen.width
rHeight.textContent = screen.height

aWidth.textContent = screen.availWidth
aHeight.textContent = screen.availHeight

pWidth.textContent = innerWidth
pHeight.textContent = innerHeight

dWidth.textContent = document.body.clientWidth
dHeight.textContent = document.body.clientHeight

//doWidth.textContent = document.body.offsetWidth
//doHeight.textContent = document.body.offsetHeight

//sWidth.textContent = document.body.scrollWidth
//sHeight.textContent = document.body.scrollHeight

pAspect.textContent = devicePixelRatio

userA.textContent = navigator.userAgent



function isRetina(){
  // source https://en.wikipedia.org/wiki/Retina_Display#Models
  var knownRetinaResolutions = [[272,340], [312,390], [960,640], [1136,640 ], [1334,750 ], [1920,1080], [2048,1536], [2732,2048], [2304,1440], [2560,1600], [2880,1800], [4096,2304], [5120,2880]];
  var knownPhones =  [[960,640], [1136,640 ], [1334,750 ], [1920,1080]];
  var knownPads =  [[2048,1536], [2732,2048]];
  var knownBooks = [[2304,1440], [2560,1600], [2880,1800], [4096,2304], [5120,2880]];

  var hasRetinaRes = knownRetinaResolutions.some(known => known[0] === screen.width && known[1] === screen.height);
  var isACrapple = /(iPhone|iPad|iPod|Mac OS X|MacPPC|MacIntel|Mac_PowerPC|Macintosh)/.test(navigator.userAgent);
  var hasPhoneRes =  knownPhones.some(known => known[0] === screen.width && known[1] === screen.height);
  var isPhone = /iPhone/.test(navigator.userAgent);
  var hasPadRes =  knownPads.some(known => known[0] === screen.width && known[1] === screen.height);
  var isPad = /iPad/.test(navigator.userAgent);
  var hasBookRes =  knownBooks.some(known => known[0] === screen.width && known[1] === screen.height);
  var isBook = /Mac OS X|MacPPC|MacIntel|Mac_PowerPC|Macintosh/.test(navigator.userAgent);

  var isAgentMatchingRes = (isBook && hasBookRes && !isPad && !isPhone) ||
      (isPad && hasPadRes && !isBook && !isPhone) ||
      (isPhone && hasPhoneRes && !isBook && !isPad)
  return devicePixelRatio >= 2 && 
         isACrapple && 
         hasRetinaRes && 
          isAgentMatchingRes;
}

guess.textContent = isRetina() ? "Yes" : "No";

＆＃13;

div, h1, span {
  font-family : arial;
}
span {
  font-weight : bold
}

＆＃13;

<div class="r-display" id="info">
  <h1>System info</h1>
  <div>Device resolution : 
    <span id = "rWidth"></span> by <span id = "rHeight"></span> pixels
  </div>
  <div>Availabe resolution : 
    <span id = "aWidth"></span> by <span id = "aHeight"></span> pixels
  </div>
  <div>Page resolution : 
    <span id = "pWidth"></span> by <span id = "pHeight">  </span> CSS pixels
  </div>
  <div>Document client res : 
    <span id = "dWidth"></span> by <span id = "dHeight">  </span> CSS pixels
  </div>
  <div>Pixel aspect : 
    <span id = "pAspect"></span>
  </div>
  <div>User agent :
    <span id="userA"></span>
  </div>
  <h3>Best guess is retina "<span id = "guess"></span>!"</h3>
</div>

＆＃13;

从您的代码段

这可能会做你想要的。因为我不拥有任何苹果产品，所以除了在isRetina上强制执行之外我无法测试它。

＆＃13;

    function isRetina() {
        // source https://en.wikipedia.org/wiki/Retina_Display#Models
        var knownRetinaResolutions = [[272, 340], [312, 390], [960, 640], [1136, 640], [1334, 750], [1920, 1080], [2048, 1536], [2732, 2048], [2304, 1440], [2560, 1600], [2880, 1800], [4096, 2304], [5120, 2880]];
        var knownPhones = [[960, 640], [1136, 640], [1334, 750], [1920, 1080]];
        var knownPads = [[2048, 1536], [2732, 2048]];
        var knownBooks = [[2304, 1440], [2560, 1600], [2880, 1800], [4096, 2304], [5120, 2880]];

        var hasRetinaRes = knownRetinaResolutions.some(known => known[0] === screen.width && known[1] === screen.height);
        var isACrapple = /(iPhone|iPad|iPod|Mac OS X|MacPPC|MacIntel|Mac_PowerPC|Macintosh)/.test(navigator.userAgent);
        var hasPhoneRes = knownPhones.some(known => known[0] === screen.width && known[1] === screen.height);
        var isPhone = /iPhone/.test(navigator.userAgent);
        var hasPadRes = knownPads.some(known => known[0] === screen.width && known[1] === screen.height);
        var isPad = /iPad/.test(navigator.userAgent);
        var hasBookRes = knownBooks.some(known => known[0] === screen.width && known[1] === screen.height);
        var isBook = /Mac OS X|MacPPC|MacIntel|Mac_PowerPC|Macintosh/.test(navigator.userAgent);

        var isAgentMatchingRes = (isBook && hasBookRes && !isPad && !isPhone) ||
            (isPad && hasPadRes && !isBook && !isPhone) ||
            (isPhone && hasPhoneRes && !isBook && !isPad);
      
      
        return devicePixelRatio >= 2 && isACrapple && hasRetinaRes && isAgentMatchingRes;
    }
    
    function svgToImage(svg){
        function svgAsImg() {
            var canvas, ctx;
            canvas = document.createElement("canvas");
            ctx = canvas.getContext("2d");
            var width = this.width;
            var height = this.height;
            var scale = 1;
            if(isRetina()){
                width *= 2;
                height *= 2;
                scale = 2;
            }

            canvas.width = width;
            canvas.height = height;
            ctx.setTransform(scale, 0, 0, scale, 0, 0);
            ctx.imageSmoothingEnabled = false;  // SVG rendering is better with smoothing off
            ctx.drawImage(this,0,0);
            DOMURL.revokeObjectURL(url);
            try{
                var image = new Image();
                image.src = canvas.toDataURL();              
                imageContainer.appendChild(image);
                image.width = this.width;
                image.height = this.height;
            }catch(e){  // in case of CORS error fallback to canvas
                canvas.style.width = this.width + "px";  // in CSS pixels not physical pixels
                canvas.style.height = this.height + "px";
                imageContainer.appendChild(canvas);  // just use the canvas as it is an image as well
            }
        };
        var url;
        var img = new Image();
        var DOMURL = window.URL || window.webkitURL || window;
        img.src = url = DOMURL.createObjectURL(new Blob([svg], {type: 'image/svg+xml'}));           
        img.onload = svgAsImg;
    }
    
    svgToImage(svgContainer.innerHTML);

＆＃13;

<div id="svgContainer"><svg width="31" height="40" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 43 55" fill="#736b9e"><path d="m 40.713968,30.966202 c 0.0028,0.05559 -0.01078,0.114956 -0.044,0.178882 -1.545645,2.974287 -2.853499,5.591663 -4.339695,7.673668 -0.788573,1.104704 -2.095869,2.778673 -2.874223,3.773068 -0.994236,1.02684 -6.879641,7.657944 -6.167884,7.049648 -1.292899,1.235403 -5.717368,5.476022 -5.717368,5.476022 0,0 -4.323294,-3.985179 -5.928388,-5.591297 C 14.037321,47.920078 10.708239,43.994015 9.6976253,42.770306 8.6870114,41.546601 8.5086687,40.900753 6.8441265,38.818752 5.8958518,37.63265 4.1376268,34.24638 3.0745121,32.156026 2.9037625,31.86435 2.7398218,31.568267 2.5826899,31.268005 2.5509386,31.228498 2.5238331,31.18779 2.5044312,31.145084 2.4575955,31.041974 2.4164305,30.951055 2.3805569,30.87146 0.95511134,28.003558 0.15221914,24.771643 0.15221914,21.351725 c 0,-11.829154 9.58943056,-21.41858234 21.41858286,-21.41858234 11.829152,0 21.418583,9.58942834 21.418583,21.41858234 0,3.457576 -0.820406,6.72314 -2.275417,9.614477 z M 21.52596,1.5031489 c -10.866018,0 -19.6746717,8.8086521 -19.6746717,19.6746741 0,10.866016 8.8086537,19.674669 19.6746717,19.674669 10.866018,0 19.674672,-8.808648 19.674672,-19.674669 0,-10.866022 -8.808654,-19.6746741 -19.674672,-19.6746741 z" /><g transform="translate(6.5,6) scale(0.060546875)"><path d="M32 384h272v32H32zM400 384h80v32h-80zM384 447.5c0 17.949-14.327 32.5-32 32.5-17.673 0-32-14.551-32-32.5v-95c0-17.949 14.327-32.5 32-32.5 17.673 0 32 14.551 32 32.5v95z"></path><g><path d="M32 240h80v32H32zM208 240h272v32H208zM192 303.5c0 17.949-14.327 32.5-32 32.5-17.673 0-32-14.551-32-32.5v-95c0-17.949 14.327-32.5 32-32.5 17.673 0 32 14.551 32 32.5v95z"></path></g><g><path d="M32 96h272v32H32zM400 96h80v32h-80zM384 159.5c0 17.949-14.327 32.5-32 32.5-17.673 0-32-14.551-32-32.5v-95c0-17.949 14.327-32.5 32-32.5 17.673 0 32 14.551 32 32.5v95z"></path></g></g></svg>
</div>    
<div id="imageContainer"></div>

＆＃13;

请注意。

大多数拥有6/6视力（帝国20/20）的人都很难看到画布略显模糊的显示与清晰的DOM之间的区别。你应该问自己，你需要仔细看看才能确定吗？你能看到正常观看距离的模糊吗？

也有些人将显示器缩放到200％是出于正当理由（视力受损），并且不会感谢你规避他们的设置。

SVG呈现在视网膜显示屏上模糊的画布上

1 个答案:

视网膜显示

一些解决方案

更好的猜猜

从您的代码段