如何使用 Javascript 将图标字体渲染为图片
前言
在软件开发中肯定要用到图标，比如下图的 Groove 音乐中就用到了许多图标。一种获取这些图标的方法是把 Groove 音乐截个图，然后熟练地开启 Photoshop，开始抠图。这种方式很逊，效率也很低（虽然我刚开始就是这么干的）。
如果打开 C:/Program Files/WindowsApps（需要修改权限才能进入），可以发现几个名字里带 ZuneMusic 的文件夹，其中的某一个文件夹中会有字体文件 SegMVR2.ttf。这是一个图标字体文件，双击安装之后，打开 Windows 自带的字符映射表应用，将字体换为 Segoe MVR MDL2 Assets，可以看到里面的字符其实就是图标。其实可以用 Metro Studio 将这些字体导出为 png、svg 等格式的图片，但是 Metro Studio 导出的字符看起来很细，也无法分别控制上下和左右的内边距，所以这里改用 Javascript 操作 canvas 绘制图标，然后导出为 png。
实现方式
在 CodePen 上已经有人给出了将 Microsoft 开源的 Fabric UI Icon 渲染为 png 图片的 demo，效果很不错。阅读源代码之后可以发现，他在 getFontIconCharacter() 先创建了一个临时的元素，根据想要的图标的名字设置元素的 className，获取::before 伪元素的 content 中字符的 Unicode，接着在 drawIcon() 中使用 context.fillText() 方法绘制字符，最后 canvas.toDataURL() 就能将 canvas 的内容转换为 base64 格式的图片。
可以看到，对于自定义的的字体，我们只需知道字符的 Unicode，就能实现导出功能。
html
html 和 coepen 中的几乎完全一样，唯一不同的地方就是将 font-class 换成了 font-unicode，因为我们只有字符的 unicode。
<html>
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" type="text/css" href="index.css">
<title>iconfont to png</title>
</head>
<body>
<div class="ms-Grid" dir="ltr">
<h1 class="ms-font-su">Render Office Fabric UI Icons into Canvas</h1>
<p>This is a simple tool to render an icon from the <a class="ms-fontColor-blueLight"
href="https://developer.microsoft.com/en-us/fabric#/styles/icons">Office Fabric UI icon font</a> into an
HTML <code><canvas></code> with a background color. Right-click and save the image to use it.</p>
<div class="ms-Grid-row">
<div class="ms-Grid-col ms-sm12 ms-lg6">
<h2 class="ms-font-xxl">Icon/Canvas Specifications</h2>
<form id="form">
<div class="ms-Grid">
<div class="ms-Grid-row">
<div class="ms-Grid-col ms-md6">
<label for="font-unicode">Icon unicode</label>
<input type="text" name="fontClass" id="font-unicode"
placeholder="e.g. ms-Icon ms-Icon-Warning" value="E768">
</div>
<div class="ms-Grid-col ms-md6">
<label for="font-size">Font size (px)</label>
<input type="number" step="1" min="1" name="fontSize" id="font-size"
placeholder="e.g. 60" value="56">
</div>
</div>
<div class="ms-Grid-row">
<div class="ms-Grid-col ms-md6">
<label for="image-width">Image width (px)</label>
<input type="number" step="1" min="0" name="imageWidth" id="image-width"
placeholder="e.g. 80" value="92">
</div>
<div class="ms-Grid-col ms-md6">
<label for="image-height">Image height (px)</label>
<input type="number" step="1" min="0" name="imageHeight" id="image-height"
placeholder="e.g. 80" value="92">
</div>
</div>
<div class="ms-Grid-row">
<div class="ms-Grid-col ms-md6">
<label for="left-offset">Left offset</label>
<input type="number" step="1" name="leftOffset" id="left-offset" placeholder="e.g. 40"
value="46">
</div>
<div class="ms-Grid-col ms-md6">
<label for="top-offset">Top offset</label>
<input type="number" step="1" name="topOffset" id="top-offset" placeholder="e.g. 40"
value="46">
</div>
</div>
<div class="ms-Grid-row">
<div class="ms-Grid-col ms-md6">
<label for="bg-color">Background color</label>
<input type="text" name="bgColor" id="bg-color" placeholder="e.g. #777777"
value=#777777>
</div>
<div class="ms-Grid-col ms-md6">
<label for="icon-color">Icon color</label>
<input type="text" name="iconColor" id="icon-color" placeholder="e.g. #FFFFFF"
value=#FFFFFF>
</div>
</div>
<div class="ms-Grid-row">
<div class="ms-Grid-col ms-sm12">
<label><input type="checkbox" checked name="shape" id="shape"> Use a circle as the
background fill</label>
</div>
</div>
</div>
<input type="submit"
class="ms-button ms-bgColor-themeDark ms-bgColor-themeDarker--hover ms-fontColor-white"
value="Render Font Icon">
<p>If the icon does not render immediately, wait a few seconds and press the <b>Render</b> button
again; the webfont may still be loading.</p>
</form>
</div>
<div class="ms-Grid-col ms-sm12 ms-lg6">
<h2 class="ms-font-xxl">Result</h2>
<div class="canvas-container">
<canvas id="canvas" width="92" height="92"></canvas>
</div>
<p><a id="download-link"
class="ms-button ms-bgColor-themeDark ms-bgColor-themeDarker--hover ms-fontColor-white"
target="_blank"><i class="ms-Icon ms-Icon--Download"></i> Download the image</a></p>
<label for="dataURL">Data URL</label>
<input id="dataURL" type="text">
</div>
</div>
</div>
</body>
<script src="index.js"></script>
</html>
css
与 codepen 中的代码相比，这里只是多了一个 @font-face 声明要使用的字体。图标的下载地址在 蓝奏云，密码为 abcr。
@import url(https://static2.sharepointonline.com/files/fabric/office-ui-fabric-core/11.0.0/css/fabric.min.css);
@font-face {
font-family: 'Segoe MVR MDL2 Assets';
src: url('SegoeMVRMDL2Assets.ttf') format('truetype');
font-weight: normal;
font-style: normal;
}
html {
box-sizing: border-box;
}
*,
*:before,
*:after {
box-sizing: inherit;
}
body {
font-family: "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif;
background-color: #0078d4;
color: white;
}
.ms-Grid {
margin: 0 auto;
padding: 0 16px;
max-width: 1280px;
}
.ms-Grid-row {
margin-left: -16px;
margin-right: -16px;
}
.ms-Grid-col {
padding: 0 16px;
}
label {
display: block;
margin-bottom: 0.5em;
}
input {
border: none;
display: block;
margin-bottom: 2em;
padding: 5px;
width: 100%;
font-size: 16px;
}
input[type="checkbox"] {
display: inline-block;
padding: 0;
width: auto;
}
input[type="button"],
input[type="submit"],
.ms-button {
cursor: pointer;
display: inline-block;
padding: 0.75em 2em;
text-decoration: none;
width: auto;
}
.ms-button .ms-Icon {
transform: translateY(2px);
}
.canvas-container {
background-color: white;
display: inline-block;
margin-bottom: 1em;
padding: 10px;
width: auto;
}
#canvas {
color: black;
font-family: FabricMDL2Icons;
}
js
这里我们主要修改了 getFontIconCharacter() 函数，直接根据输入框的内容返回字符的 Unicode。
const form = document.getElementById("form");
const canvas = document.getElementById("canvas");
const context = canvas.getContext("2d");
const download = document.getElementById("download-link");
const dataURL = document.getElementById("dataURL");
const fontFamily = "Segoe MVR MDL2 Assets";
function getFontIconCharacter(unicode) {
return String.fromCharCode(parseInt(unicode, 16));
}
function drawCircle() {
var centerX = canvas.width / 2;
var centerY = canvas.height / 2;
var radius = canvas.width / 2;
context.beginPath();
context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
context.fillStyle = document.getElementById("bg-color").value || "#777777";
context.fill();
}
function drawRect() {
context.fillStyle = document.getElementById("bg-color").value || "#777777";
context.fillRect(0, 0, canvas.width, canvas.height);
}
function drawIcon() {
canvas.width = parseInt(document.getElementById("image-width").value, 10) || 92;
canvas.height = parseInt(document.getElementById("image-height").value, 10) || 92;
context.clearRect(0, 0, canvas.width, canvas.height);
if (document.getElementById("shape").checked) {
drawCircle();
} else {
drawRect();
}
context.fillStyle = document.getElementById("icon-color").value || "#FFFFFF";
let fontUnicode = document.getElementById("font-unicode").value,
fontSize = document.getElementById("font-size").value || 280,
topOffset = document.getElementById("top-offset").value || 210,
leftOffset = document.getElementById("left-offset").value || 210;
context.font = `${fontSize}px ${fontFamily}`;
context.textAlign = "center";
context.textBaseline = "middle";
context.fillText(getFontIconCharacter(fontUnicode), parseInt(leftOffset, 10), parseInt(topOffset, 10));
dataURL.value = canvas.toDataURL();
}
window.addEventListener('load', function () {
drawIcon();
});
document.addEventListener('DOMContentLoaded', function () {
context.font = "10px " + fontFamily;
context.fillText("...", 0, 0);
});
form.addEventListener("submit", function (event) {
event.preventDefault();
drawIcon();
});
download.addEventListener("click", function (event) {
if (typeof this.download !== "undefined") {
this.href = canvas.toDataURL();
this.download = `${document.getElementById("font-unicode").value}.png`;
} else {
event.preventDefault();
alert("Your browser does not support downloading a canvas image. Please right-click on the image to save it.");
}
});
dataURL.addEventListener("focus", function (event) {
dataURL.select();
});
效果
打开 html 之后如下图所示，只需修改 Icon unicode，再点击 Render Font Icon 按钮，就能在右侧的画布中看到图标，点击 Download the image 按钮就能下载图标了。
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