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<a href="/graphics/font-rendering/" class="post-title-link" itemprop="url">字体渲染概览</a>
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<time title="创建时间：2022-08-16 20:44:13" itemprop="dateCreated datePublished" datetime="2022-08-16T20:44:13+08:00">2022-08-16</time>
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<h2 id="前⾔"><a href="#前⾔" class="headerlink" title="前⾔"></a>前⾔</h2><p>本⽂旨在介绍⽂字渲染需要了解的基本知识点，以及些许延伸扩展；不涉及到实际代码的编写，不涉及具体算法实现，但中间穿插引⽤的外部⽂档有部分代码实现可供参考。</p>
<blockquote>
<p>本文引用的图都是来源网络博文，部分图片并未记录来源。如涉及侵权请联系我。</p>
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<h2 id="字体发展历史"><a href="#字体发展历史" class="headerlink" title="字体发展历史"></a>字体发展历史</h2><ul>
<li>在 Macintosh 电脑中，使用点阵字体（格式后缀：bdf、pcf、fnt、hbf等)。点阵字体放大后会出现锯齿、模糊的情况。</li>
<li>在同一时期，Adobe 发明了基于 PostScript Type 1 的矢量字体格式，但 Type 1 字体是加密的，Adobe 通过售卖字体认证赚取利润，苹果也不得不向 Adobe 购买 Type 1 字体认证。</li>
<li>于是，苹果决定设计全新的字体格式，最后在 1991 年发布为 TrueType 格式，同时也包括 Times Roman、Helvetica、Courier 等大量字体。</li>
<li>但是 TrueType 字体反响并不好，因为大部分用户已经购买了 Adobe Type 1 字体，没必要再切换。因此，苹果联合微软对抗 Adobe，授权给微软使用 TrueType 字体。1991年，微软在 Windows 3.1 系统上支持了 TrueType，并和 MonoType 公司联合开发了大量著名字体，例如 Arial 等字体。</li>
<li>1994 年，微软独自开发了 TrueType Open 字体；1996 年 Adobe 加入开发，兼容了 Type1 字体格式，更名为 OpenType。2007 年，OpenType 被国际标准组织 (ISO）采用。OpenType 常见后缀 otf、ttf、ttc。</li>
<li>2023年，Adobe 将停止支持 Type 1 字体创作。</li>
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<br/>
<blockquote>
<p><strong>SFNT</strong>：SFNT 是苹果在开发 TrueType 字体格式时设计的通⽤字体数据存储结构，SFNT 是 spline font 或者 scalable font 的缩写，TrueType、OpenType、WOFF 等格式都采⽤ SFNT 作为容器。 </p>
<p><strong>WOFF</strong>：Web Open Font Format，采⽤压缩格式，字体⽂件更⼩，适合⽹⻚使⽤。可以简单理解为 OpenType + 压缩。⼀般⽐ ttf 字体⼩ 40%。WOFF2 是 WOFF 的下⼀代标准，在 WOFF 的基础上提⾼ 30% 的 压缩率。</p>
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<p>Objective-C 是一门动态语言。所谓动态，在于消息发送和转发，在于 Method Swizzling，同时也在于 Non-fragile ivar。之前有一篇文章简单介绍过消息发送和转发（<a href="/2016/01/24/programing/iOS/tutorial/02MethodResolve/">iOS教程（二）消息发送</a>），这一篇主要介绍下 Non-fragile ivar 特性及其实现方式。</p>
<h2 id="什么是-ivar-？"><a href="#什么是-ivar-？" class="headerlink" title="什么是 ivar ？"></a>什么是 ivar ？</h2><p>ivar（instance variable）就是类成员变量。一般情况下，property 都会自动生成一个成员变量。</p>
<p>假设有一个 MyObject 类，有 array 和 color 两个成员变量， MyObject 实例的内存结构如下：<br><img src="/images/ivar-layout.jpeg" alt="ivar-layout"></p>
<p>如果要获取 color 的值，self 指针加上偏移量，再解引用就可以了，这也是 runtime 获取成员变量的方式。</p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">UIColor</span> *color = *(<span class="built_in">UIColor</span> *)((<span class="type">char</span> *)<span class="keyword">self</span> + <span class="number">16</span>);</span><br></pre></td></tr></table></figure>
<p>当然，runtime 的逻辑比这复杂，例如 atomic 加锁等。</p>
<h2 id="什么是-Non-fragile-ivar-？"><a href="#什么是-Non-fragile-ivar-？" class="headerlink" title="什么是 Non-fragile ivar ？"></a>什么是 Non-fragile ivar ？</h2><p>fragile 的含义是脆弱的，Non-fragile ivar 解决的是 fragile ivar 的问题。</p>
<h4 id="fragile-ivar-问题"><a href="#fragile-ivar-问题" class="headerlink" title="fragile ivar 问题"></a>fragile ivar 问题</h4><p>在 32 位的 Mac 上，假定有一个 NSCustomView 继承自 NSView，NSCustomView 有两个成员变量。（至于为什么是 32 位的 Mac，接下来会介绍。）</p>
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<p>在 iOS 开发中，weak property 或者是 <code>__weak</code> 修饰的变量，在对象释放后，变量会自动置为 nil。delegate 模式、block 中 weak strong dance 都会用到。</p>
<p>比如，声明一个 weak 的 delegate。</p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">@property</span> (<span class="keyword">nonatomic</span>, <span class="keyword">weak</span>) <span class="type">id</span> delegate;</span><br></pre></td></tr></table></figure>
<p>weak 用的好可以避免内存泄漏和野指针崩溃。weak 有这么大的作用，底层具体是咋实现的呢？本文探讨下 weak 的底层实现原理。</p>
<h3 id="初探-weak-实现"><a href="#初探-weak-实现" class="headerlink" title="初探 weak 实现"></a>初探 weak 实现</h3><p>首先通过汇编来看下，底层怎么实现的。先写几行代码。</p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">{</span><br><span class="line"> <span class="type">id</span> referent = [<span class="built_in">NSObject</span> new];</span><br><span class="line"> __<span class="keyword">weak</span> <span class="type">id</span> weakObj = referent;</span><br><span class="line"> <span class="built_in">NSLog</span>(@“%@“, weakObj);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>在 Xcode 中勾选 Debug -> Debug Workflow -> Always Show Disassembly，然后在 NSLog 行加个断点，运行之后可以看到这样一段汇编代码：</p>
<p><img src="/images/weak-disassembly.png" alt="disassembly code"></p>
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<p>在我们点击屏幕的时候，系统捕获到触摸事件，系统把包含这些触摸事件的信息包装成 UITouch 和 UIEvent 实例，然后找到当前运行的应用，逐级寻找能够响应这个事件的对象，直到没有响应者响应。这一系列响应者组成了响应链。</p>
<p>首先，系统捕获到点击行为后，将点击事件封装成 UIEvent 对象。接下来，就需要确定具体触摸到哪个 view，也即是找到手指触摸到的处于屏幕最前端的 view，这一步叫 hit-testing。</p>
<h3 id="hit-testing"><a href="#hit-testing" class="headerlink" title="hit-testing"></a>hit-testing</h3><p>UIView 中有两个方法，hitTest 和 pointInside：</p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">- (<span class="built_in">UIView</span> *)hitTest:(<span class="built_in">CGPoint</span>)point withEvent:(<span class="keyword">nullable</span> <span class="built_in">UIEvent</span> *)event;</span><br><span class="line">- (<span class="type">BOOL</span>)pointInside:(<span class="built_in">CGPoint</span>)point withEvent:(<span class="keyword">nullable</span> <span class="built_in">UIEvent</span> *)event; </span><br></pre></td></tr></table></figure>
<p>pointInside 方法是判断 point 是否在当前 view 内。<br>hitTest 方法是调用 pointInside 函数判断触点是否在当前 view 内，以及递归调用子 view 的 hitTest 方法，找到实际触摸的 view。</p>
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<p>苹果在 iOS 9 开始提供 Universal Link 唤起 App 的能力。Universal Link 时机上是一个 https 链接，在用户点击网页中的 https 链接时，先尝试唤起 App，唤起失败则加载对应的网页。</p>
<p>相比于使用 <code>scheme://</code> 这种 scheme 的方式唤起 App，Universal Link 唤起的优点在于苹果并未提供接口进行拦截，一般 App 不会进行拦截。并且在唤起失败时，能自动加载对应的页面。</p>
<p>因此，业内使用 Universal Link 唤起 App的逐渐增多。用户被恶意导流至其他 App 的问题日益严重。本文研究 iOS Universal Link 唤起 App 的逻辑，找到拦截 Universal Link 的方案。</p>
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<p>这是设计模式系列第三篇博文，装饰者模式，也是《Head First 设计模式》的学习笔记。</p>
<h3 id="定义"><a href="#定义" class="headerlink" title="定义"></a>定义</h3><blockquote>
<p><strong>装饰者模式</strong> 动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。</p>
</blockquote>
<h3 id="问题"><a href="#问题" class="headerlink" title="问题"></a>问题</h3><p>老套路，为了后面讨论的需要，先简单的复述下《Head First 设计模式》中的例子（简化版）。</p>
<ol>
<li>星巴克中有一系列的咖啡（Coffee），其中一种为 DarkRoast。</li>
<li>咖啡可以配上不同的调料，假设有两种调料 Mocha 和 Whip。</li>
<li>顾客点咖啡之后，可以自主选择调料。</li>
</ol>
<p>在这三个条件之下，要怎么来设计星巴克的点单系统，以计算出最后的价格？</p>
<p>可以把咖啡和调料都抽象成顾客需要消费的产品（Beverage），咖啡对象和调料对象都实现 Beverage 协议。</p>
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<p>也不是经常使用 Python，每次用时都忘的差不多，又需要重新查资料。所以，开篇博客记录下这些琐碎的知识点。<br>都是入门基础级别的知识点，大神请出门左拐👋👋。</p>
<h4 id="获取日期"><a href="#获取日期" class="headerlink" title="获取日期"></a>获取日期</h4><p><a target="_blank" rel="noopener" href="https://docs.python.org/2/library/datetime.html">Python lib doc: datetime</a></p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> datetime</span><br><span class="line"></span><br><span class="line"><span class="comment"># 按格式打印当前时间</span></span><br><span class="line"><span class="built_in">print</span> datetime.datetime.now().strftime(<span class="string">'%m-%d'</span>)</span><br><span class="line"></span><br><span class="line"><span class="comment"># 按格式打印昨天时间</span></span><br><span class="line">delta = datetime.timedelta(<span class="number">1</span>)</span><br><span class="line">yestoday = datetime.datetime.now() - delta</span><br><span class="line"><span class="built_in">print</span> yestoday.strftime(<span class="string">'%m-%d'</span>)</span><br></pre></td></tr></table></figure>
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<p>这是设计模式系列第二篇博文，观察者模式，也是《Head First 设计模式》的学习笔记。</p>
<h3 id="定义"><a href="#定义" class="headerlink" title="定义"></a>定义</h3><blockquote>
<p>主题（Subject）：主题对象管理某些数据。<br>观察者（Observer）：监听主题的数据变化，执行响应的操作。</p>
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<p><strong>观察者模式</strong> 定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，它的所有依赖者都会收到通知并自动更新。</p>
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<h3 id="讨论"><a href="#讨论" class="headerlink" title="讨论"></a>讨论</h3><p>在日常开发中，经常用到观察者模式，相信大家都已经对观察者模式烂熟于心。但是是不是真的用的好呢？我提几个问题，看看大家是否有思考过，也欢迎留言讨论。</p>
<h4 id="通知数据更新，是选择以推的方式来实现还是以拉的方式来实现？各有哪些优缺点？"><a href="#通知数据更新，是选择以推的方式来实现还是以拉的方式来实现？各有哪些优缺点？" class="headerlink" title="通知数据更新，是选择以推的方式来实现还是以拉的方式来实现？各有哪些优缺点？"></a>通知数据更新，是选择以推的方式来实现还是以拉的方式来实现？各有哪些优缺点？</h4><p>我们先定义下推和拉。<br><strong>推的方式</strong>：通知 Observer 数据有更新时，通知把更新后的数据通过参数一起传递过去；<br><strong>拉的方式</strong>：数据更新时，只通知 Observer 数据有更新，具体需要哪些数据由 Observer 主动调 Subject 的接口查询。</p>
<p>拉的方式，Observer 并不知道具体更新的数据是哪些。收到数据更新时，只能一股脑的把自己需要的数据都重新查询一遍，有时候是很低效的。其次，有时候 Observer 需要知道更新前的数据以及更新后的数据，使用拉的方式也无法解决这种场景。</p>
<p>如果选择推的方式，以上两个缺点都可以解决。但是同时也带来了一个新的问题。在推的方式中，更新的数据是以参数来传递的。当需要新增参数时，就需要修改所有 Observer 的方法，略蛋疼。</p>
<p>但其实也不是没有解决方法，可以使用一个 model 来传递。当通知更新的参数大于三个时，建议以传递 model 的方式来通知更新。</p>
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<p>最近 Vultr 的 VPS 越来越不给力，挂在 Vultr VPS 上的博客加载速度越来越慢。遂决定将博客迁回 github pages。</p>
<p>其实很简单，两步搞定：</p>
<ul>
<li>首先，在 github 博客仓库根目录下新建一个文件，文件名<code>CNAME</code>，文件内容为自定义的域名，例如：blog.duxevr.com</li>
<li>在 DNS 服务商那增加一个<code>CNAME</code>记录，指向 github 博客的地址。<br>github 博客的 url 为 YOUR-GITHUB-NAME.github.io，例如我的 github 博客url为：jefferyfan.github.io。</li>
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<p>Hexo 配置相关文章：</p>
<ul>
<li><a href="/2016/07/24/guide/hexo-custom-host-vps/">Hexo博客自定义域名和部署到VPS</a></li>
<li><a href="/2015/07/22/guide/hexo-guide/">Hexo博客使用教程</a></li>
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