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---
title: CanvasRenderingContext2D.textBaseline
slug: Web/API/CanvasRenderingContext2D/textBaseline
tags:
- Canvas
- CanvasRenderingContext2D
translation_of: Web/API/CanvasRenderingContext2D/textBaseline
---
<div>{{APIRef}}</div>
<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.textBaseline</code></strong> 是 Canvas 2D API 描述绘制文本时，当前文本基线的属性。</p>
<blockquote>
<p>译者注：决定文字垂直方向的对齐方式。</p>
</blockquote>
<h2 id="语法">语法</h2>
<pre class="syntaxbox"><var><em>ctx</em>.textBaseline = "top" || "hanging" || "middle" || "alphabetic" || "ideographic" || "bottom";</var>
</pre>
<h3 id="选项">选项</h3>
<p>有效值：</p>
<dl>
<dt>top</dt>
<dd>文本基线在文本块的顶部。</dd>
<dt>hanging</dt>
<dd>文本基线是悬挂基线。</dd>
<dt>middle</dt>
<dd>文本基线在文本块的中间。</dd>
<dt>alphabetic</dt>
<dd>文本基线是标准的字母基线。</dd>
<dt>ideographic</dt>
<dd>文字基线是表意字基线；如果字符本身超出了alphabetic 基线，那么ideograhpic基线位置在字符本身的底部。</dd>
<dt>bottom</dt>
<dd>文本基线在文本块的底部。 与 ideographic 基线的区别在于 ideographic 基线不需要考虑下行字母。</dd>
</dl>
<p>默认值是 <code>alphabetic。</code></p>
<h2 id="示例">示例</h2>
<h3 id="Using_the_textBaseline_property" name="Using_the_textBaseline_property">使用 <code>textBaseline</code> 属性</h3>
<p>这是一段简单的代码片段，使用 <code>textBaseline</code> 属性设置不同的文本基线。</p>
<h4 id="HTML">HTML</h4>
<pre class="brush: html"><canvas id="canvas" width="550" height="500"></canvas></pre>
<h4 id="JavaScript">JavaScript</h4>
<pre class="brush: js">const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
const baselines = ['top', 'hanging', 'middle', 'alphabetic', 'ideographic', 'bottom'];
ctx.font = '36px serif';
ctx.strokeStyle = 'red';
baselines.forEach(function (baseline, index) {
ctx.textBaseline = baseline;
let y = 75 + index * 75;
ctx.beginPath();
ctx.moveTo(0, y + 0.5);
ctx.lineTo(550, y + 0.5);
ctx.stroke();
ctx.fillText('Abcdefghijklmnop (' + baseline + ')', 0, y);
});</pre>
<div class="hidden">
<h6 id="Playable_code" name="Playable_code">Playable code</h6>
<pre class="brush: html"><canvas id="canvas" width="550" height="500"></canvas></pre>
<pre class="brush: js">const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
const baselines = ['top', 'hanging', 'middle', 'alphabetic', 'ideographic', 'bottom'];
ctx.font = '36px serif';
ctx.strokeStyle = 'red';
baselines.forEach(function (baseline, index) {
ctx.textBaseline = baseline;
let y = 75 + index * 75;
ctx.beginPath();
ctx.moveTo(0, y + 0.5);
ctx.lineTo(550, y + 0.5);
ctx.stroke();
ctx.fillText('Abcdefghijklmnop (' + baseline + ')', 0, y);
});</pre>
</div>
<h4 id="结果">结果</h4>
<p>{{ EmbedLiveSample('Playable_code', 700, 550) }}</p>
<h2 id="规范描述">规范描述</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-textbaseline", "CanvasRenderingContext2D.textBaseline")}}</td>
<td>{{Spec2('HTML WHATWG')}}</td>
<td></td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p>{{Compat("api.CanvasRenderingContext2D.textBaseline")}}</p>
<h2 id="参见">参见</h2>
<ul>
<li>接口定义，{{domxref("CanvasRenderingContext2D")}}.</li>
</ul>
|
