基于canvas，通过toDataURL动态生成base64图片。目前我主题的Gravatar头像，就是利用这个LetterAvatar脚本实现未设置Gravatar头像则读取ALT标签，自动生成首字图片替代默认的头像图片。
之前已有WP爱好者制作了一款：mk-letter-avatar 字母头像插件，试了一下很好用，不过打开浏览器开者工具发现产生大量404错误，看了一下源代码，该插件是通过无头像返回404错误，触发onerror事件用自动生成的字母图片替换src图片地址，判断方式不是很合理，如果不是因为个缺点我都想直接拿来用了，如果作者再优化一下，绝对是款优秀实用的插件。
我的实现原理和插件不同，配合头像本地缓存功能，判断无头像后，直接为无头像的图片添加特定的class类，然后通过LetterAvatar脚本替换图片。
需要注意的是上面提到的插件，Gravatar头像图片必须有alt标签属性，否则不会生成正常的图片，可惜大部分主题默认Gravatar头像alt标签属性是空的…..
如果想自动为Gravatar头像添加alt标签属性，可以将下面的代码添加到当前主题函数模板functions.php中：
function zm_gravatar_alt($altgravatar) {if (have_comments()) {$alt = get_comment_author();}else {$alt = get_the_author_meta('display_name');}$altgravatar= str_replace('alt=''', 'alt='' . $alt . '' title='Gravatar for ' . $alt . ''', $altgravatar); return $altgravatar; } add_filter('get_avatar', 'zm_gravatar_alt');
之后，自动将评论者昵称做为alt属性。
本文只是自己做个记录，并不是教大家怎么弄这个头像，如果认为这字母头像还不错，请直接使用上面介绍的插件。 展开收缩
另附LetterAvatar脚本演示代码：
<!DOCTYPE html><html><h1>Letter Avatar</h1> <small><strong>用法:</strong></small> <pre> <code><img src="" class="avatar photo" width="256" height="256" alt="星空站长网" color="#c40000"></code> </pre> <img src="" class="avatar photo" height="240" width="240" alt="星空站长网" color="#c40000" /> <img src="" class="avatar photo" height="240" width="240" alt="站长" color="#99CC66" /> <img src="" class="avatar photo" height="240" width="240" alt="网" color="#0D8ABC" /><style>body {font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;}pre {margin: 20px 0;padding: 20px;background: #fafafa;}.avatar {border-radius: 50%;}</style><script src="https://libs.baidu.com/jquery/3.2.1/jquery.min.js "></script><script>/* * LetterAvatar * * Artur Heinze * Create Letter avatar based on Initials * based on https://gist.github.com/leecrossley/6027780 */(function(w, d) {function LetterAvatar(name, size, color) {name = name || '';size = size || 60;var colours = ["#1abc9c", "#2ecc71", "#3498db", "#9b59b6", "#34495e", "#16a085", "#27ae60", "#2980b9", "#8e44ad", "#2c3e50", "#f1c40f", "#e67e22", "#e74c3c", "#ecf0f1", "#95a5a6", "#f39c12", "#d35400", "#c0392b", "#bdc3c7", "#7f8c8d"],nameSplit = String(name).split(' '),initials, charIndex, colourIndex, canvas, context, dataURI;if(nameSplit.length == 1) {initials = nameSplit[0] ? nameSplit[0].charAt(0) : '?';} else {initials = nameSplit[0].charAt(0) + nameSplit[1].charAt(0);}if(w.devicePixelRatio) {size = (size * w.devicePixelRatio);}charIndex = (initials == '?' ? 72 : initials.charCodeAt(0)) - 64;colourIndex = charIndex % 20;canvas = d.createElement('canvas');canvas.width = size;canvas.height = size;context = canvas.getContext("2d");context.fillStyle = color ? color : colours[colourIndex - 1];context.fillRect(0, 0, canvas.width, canvas.height);context.font = Math.round(canvas.width / 2) + "px Arial";context.textAlign = "center";context.fillStyle = "#FFF";context.fillText(initials, size / 2, size / 1.5);dataURI = canvas.toDataURL();canvas = null;return dataURI;}LetterAvatar.transform = function() {Array.prototype.forEach.call(d.querySelectorAll('img[alt]'), function(img, name, color) {name = img.getAttribute('alt');color = img.getAttribute('color');img.src = LetterAvatar(name, img.getAttribute('width'), color);img.removeAttribute('avatar');img.setAttribute('alt', name);});}; // AMD support if (typeof define === 'function' && define.amd) { define(function () { return LetterAvatar; }); // CommonJS and Node.js module support. } else if (typeof exports !== 'undefined') { // Support Node.js specific `module.exports` (which can be a function) if (typeof module != 'undefined' && module.exports) { exports = module.exports = LetterAvatar; } // But always support CommonJS module 1.1.1 spec (`exports` cannot be a function) exports.LetterAvatar = LetterAvatar; } else { window.LetterAvatar = LetterAvatar; d.addEventListener('DOMContentLoaded', function(event) { LetterAvatar.transform(); }); } })(window, document);</script></html>
