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下面由WordPress技巧欄目給大家介紹關(guān)于用字母替代圖片腳本：LetterAvatar，希望對(duì)需要的朋友有所幫助！
基于canvas，通過toDataURL動(dòng)態(tài)生成base64圖片。目前我主題的Gravatar頭像，就是利用這個(gè)LetterAvatar腳本實(shí)現(xiàn)未設(shè)置Gravatar頭像則讀取ALT標(biāo)簽，自動(dòng)生成首字圖片替代默認(rèn)的頭像圖片。
之前已有WP愛好者制作了一款：mk-letter-avatar 字母頭像插件，試了一下很好用，不過打開瀏覽器開者工具發(fā)現(xiàn)產(chǎn)生大量404錯(cuò)誤，看了一下源代碼，該插件是通過無頭像返回404錯(cuò)誤，觸發(fā)onerror事件用自動(dòng)生成的字母圖片替換src圖片地址，判斷方式不是很合理，如果不是因?yàn)閭€(gè)缺點(diǎn)我都想直接拿來用了，如果作者再優(yōu)化一下，絕對(duì)是款優(yōu)秀實(shí)用的插件。
我的實(shí)現(xiàn)原理和插件不同，配合頭像本地緩存功能，判斷無頭像后，直接為無頭像的圖片添加特定的class類，然后通過LetterAvatar腳本替換圖片。
需要注意的是上面提到的插件，Gravatar頭像圖片必須有alt標(biāo)簽屬性，否則不會(huì)生成正常的圖片，可惜大部分主題默認(rèn)Gravatar頭像alt標(biāo)簽屬性是空的…..
如果想自動(dòng)為Gravatar頭像添加alt標(biāo)簽屬性，可以將下面的代碼添加到當(dāng)前主題函數(shù)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，自動(dòng)將評(píng)論者昵稱做為alt屬性。
本文只是自己做個(gè)記錄，并不是教大家怎么弄這個(gè)頭像，如果認(rèn)為這字母頭像還不錯(cuò)，請(qǐng)直接使用上面介紹的插件。
另附LetterAvatar腳本演示代碼：
<!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="知更鳥" color="#c40000"></code> </pre> <img src="" class="avatar photo" height="240" width="240" alt="知更鳥" color="#c40000" /> <img src="" class="avatar photo" height="240" width="240" alt="更鳥" color="#99CC66" /> <img src="" class="avatar photo" height="240" width="240" alt="鳥" 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>
原項(xiàng)目地址：https://github.com/daolavi/LetterAvatar
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