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)。

Groove

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。

字符映射表

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>&lt;canvas&gt;</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。

效果

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