前言
在軟體開發中肯定要用到圖示，比如下圖的 Groove 音樂中就用到了許多圖示。一種獲取這些圖示的方法是把 Groove 音樂截個圖，然後熟練地開啟 Photoshop，開始摳圖。這種方式很遜，效率也很低（雖然我剛開始就是這麼幹的）。
如果開啟 C:/Program Files/WindowsApps（需要修改許可權才能進入），可以發現幾個名字裡帶 ZuneMusic 的資料夾，其中的某一個資料夾中會有字型檔案 SegMVR2.ttf。這是一個圖示字型檔案，雙擊安裝之後，開啟 Windows 自帶的字元對映表應用，將字型換為 Segoe MVR MDL2 Assets，可以看到裡面的字元其實就是圖示。其實可以用 Metro Studio 將這些字型匯出為 png、svg 等格式的圖片，但是 Metro Studio 匯出的字元看起來很細，也無法分別控制上下和左右的內邊距，所以這裡改用 Javascript 操作 canvas 繪製圖示，然後匯出為 png。
實現方式
在 CodePen 上已經有人給出了將 Microsoft 開源的 Fabric UI Icon 渲染為 png 圖片的 demo，效果很不錯。閱讀原始碼之後可以發現，他在 getFontIconCharacter() 先建立了一個臨時的元素，根據想要的圖示的名字設定元素的 className，獲取::before 偽元素的 content 中字元的 Unicode，接著在 drawIcon() 中使用 context.fillText() 方法繪製字元，最後 canvas.toDataURL() 就能將 canvas 的內容轉換為 base64 格式的圖片。
可以看到，對於自定義的的字型，我們只需知道字元的 Unicode，就能實現匯出功能。
html
html 和 coepen 中的幾乎完全一樣，唯一不同的地方就是將 font-class 換成了 font-unicode，因為我們只有字元的 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
與 codepen 中的程式碼相比，這裡只是多了一個 @font-face 宣告要使用的字型。圖示的下載地址在 藍奏雲，密碼為 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
這裡我們主要修改了 getFontIconCharacter() 函式，直接根據輸入框的內容返回字元的 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
開啟 html 之後如下圖所示，只需修改 Icon unicode，再點選 Render Font Icon 按鈕，就能在右側的畫布中看到圖示，點選 Download the image 按鈕就能下載圖示了。
