我有一个SVG渲染到画布的问题.在视网膜上显示画布呈现为base64网址并设置为SRC模糊.
我尝试了下面列表中描述的各种方法,没有运气：
> https://tristandunn.com/2014/01/24/rendering-svg-on-canvas/
> How do I fix blurry text in my HTML5 canvas?
> Canvas drawing and Retina display: doable?
> https://www.html5rocks.com/en/tutorials/canvas/hidpi/
现在我不知道我该怎么做才能让它变得更好.
请查看我的结果：jsfiddle.net/a8bj5fgj/2/
编辑：
更新了小提琴：jsfiddle.net/a8bj5fgj/7/
解决方法:
Retina显示屏
视网膜和非常高分辨率的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规则图像渲染来完成：像素化;虽然这不会创建在DOM上呈现的SVG的质量,但它将减少一些用户体验的模糊外观.
>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.
为此,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,并且devicePixelRatio受页面缩放设置的影响.
所以在最基本的使用devicePixelRatio和假设很少人放大200％.
代码假设canvas.style.width和canvas.style.height已经正确设置.
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);
}
Note I do not increase the pixel size by the value of “devicePixelRatio” This is because retina devices will only have a resolution of 2 times, if the aspect ratio is greater than 2 it is because the client has zoomed in. To honor the expected behaviour of the canvas I do not adjust for zoom setting if I can. Though that is not a rule just a suggestion.
更好的猜测
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.
目前,Retina显示器采用固定的一组分辨率,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来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.
把它们放在一起你可以改善猜测.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.
在wiki Retina Display Models找到以下代码的信息如果要使其保持最新,可以使用Wiki的SPARQL接口对此信息进行机器查询.
演示猜猜视网膜.
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";
div, h1, span {
font-family : arial;
}
span {
font-weight : bold
}<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>
从你的片段
这可能会做你想要的.由于我没有任何苹果产品,我无法测试它除了在isRetina上强制执行.
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);
<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>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％这样做是有充分理由的(视力受损)并且不会欣赏你绕过他们的设置.