---
title: CanvasRenderingContext2D.lineJoin
slug: Web/API/CanvasRenderingContext2D/lineJoin
translation_of: Web/API/CanvasRenderingContext2D/lineJoin
---
<div>{{APIRef}}</div>

<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.lineJoin</code></strong> 是 Canvas 2D API 用来设置2个长度不为0的相连部分（线段，圆弧，曲线）如何连接在一起的属性（长度为0的变形部分，其指定的末端和控制点在同一位置，会被忽略）。</p>

<p>参见 <a href="/en-US/docs/Web/API/Canvas_API/Tutorial">Canvas Tutorial</a> 中的 <a href="/en-US/docs/Web/API/Canvas_API/Tutorial/Applying_styles_and_colors">Applying styles and color</a> 章节。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox"><var><em>ctx</em>.lineJoin = "bevel";
<var><em>ctx</em>.lineJoin = "round";
<var><em>ctx</em>.lineJoin = "miter";</var></var></var></pre>

<h3 id="选项">选项</h3>

<p>此属性有3个值： <code>round</code>, <code>bevel</code> and <code>miter</code>。默认值是 <code>miter。注意：如果2个相连部分在同一方向，那么lineJoin不会产生任何效果</code>，因为在那种情况下不会出现连接区域。</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/237/Canvas_linejoin.png" style="float: right; height: 190px; width: 190px;"></p>

<dl>
 <dt><code>round</code></dt>
 <dd>通过填充一个额外的，圆心在相连部分末端的扇形，绘制拐角的形状。 圆角的半径是线段的宽度。</dd>
 <dt><code>bevel</code></dt>
 <dd>在相连部分的末端填充一个额外的以三角形为底的区域， 每个部分都有各自独立的矩形拐角。</dd>
 <dt><code>miter</code></dt>
 <dd>通过延伸相连部分的外边缘，使其相交于一点，形成一个额外的菱形区域。这个设置可以通过 {{domxref("CanvasRenderingContext2D.miterLimit", "miterLimit")}} 属性看到效果。</dd>
</dl>

<h2 id="示例">示例</h2>

<h3 id="Using_the_lineCap_property" name="Using_the_lineCap_property">使用 <code>lineJoin</code> 属性</h3>

<p>这是一段使用 <code>lineJoin</code> 属性的简单的代码片段。</p>

<h4 id="HTML">HTML</h4>

<pre class="brush: html">&lt;canvas id="canvas"&gt;&lt;/canvas&gt;
</pre>

<h4 id="JavaScript">JavaScript</h4>

<pre class="brush: js; highlight[5]">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.lineWidth = 10;
ctx.lineJoin = "round";
ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineTo(200, 100);
ctx.lineTo(300,0);
ctx.stroke();
</pre>

<p>修改下面的代码并在线查看 canvas 的变化：</p>

<div class="hidden">
<h6 id="Playable_code" name="Playable_code">Playable code</h6>

<pre class="brush: html">&lt;canvas id="canvas" width="400" height="200" class="playable-canvas"&gt;&lt;/canvas&gt;
&lt;div class="playable-buttons"&gt;
  &lt;input id="edit" type="button" value="Edit" /&gt;
  &lt;input id="reset" type="button" value="Reset" /&gt;
&lt;/div&gt;
&lt;textarea id="code" class="playable-code" style="height:120px;"&gt;
ctx.lineWidth = 10;
ctx.lineJoin = "round";
ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineTo(200, 100);
ctx.lineTo(300,0);
ctx.stroke();&lt;/textarea&gt;
</pre>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);
</pre>
</div>

<p>{{ EmbedLiveSample('Playable_code', 700, 380) }}</p>

<h3 id="A_lineJoin_example" name="A_lineJoin_example"><code>lineJoin</code> 例子</h3>

<p>下面的例子绘制了3条不同的路径，演示 <code>lineJoin</code> 属性3种不同的设置。</p>

<pre class="brush: js">var ctx = document.getElementById('canvas').getContext('2d');
var lineJoin = ['round','bevel','miter'];
ctx.lineWidth = 10;

for (var i = 0; i &lt; lineJoin.length; i++) {
  ctx.lineJoin = lineJoin[i];
  ctx.beginPath();
  ctx.moveTo(-5,5+i*40);
  ctx.lineTo(35,45+i*40);
  ctx.lineTo(75,5+i*40);
  ctx.lineTo(115,45+i*40);
  ctx.lineTo(155,5+i*40);
  ctx.stroke();
}
</pre>

<div class="hidden">
<pre class="brush: html">&lt;canvas id="canvas" width="150" height="150"&gt;&lt;/canvas&gt;</pre>
</div>

<p>{{EmbedLiveSample("A_lineJoin_example", "180", "180", "https://mdn.mozillademos.org/files/237/Canvas_linejoin.png")}}</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-linejoin", "CanvasRenderingContext2D.lineJoin")}}</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>{{CompatibilityTable}}</p>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<h3 id="WebKitBlink-specific_注解">WebKit/Blink-specific 注解</h3>

<ul>
 <li>基于WebKit- 和 Blink- 的浏览器中， 实现了一个不标准的并且不赞成使用的方法 <code>ctx.setLineJoin()</code> 。</li>
</ul>

<h2 id="参见">参见</h2>

<ul>
 <li>接口定义， {{domxref("CanvasRenderingContext2D")}}</li>
 <li>{{domxref("CanvasRenderingContext2D.lineCap")}}</li>
 <li>{{domxref("CanvasRenderingContext2D.lineWidth")}}</li>
</ul>