---
title: CanvasRenderingContext2D.setLineDash()
slug: Web/API/CanvasRenderingContext2D/setLineDash
tags:
  - API
  - Canvas
  - CanvasRenderingContext2D
  - Dashes
  - LInes
  - Method
  - setLineDash
translation_of: Web/API/CanvasRenderingContext2D/setLineDash
---
<div>{{APIRef}}</div>

<p>Canvas 2D API的{{domxref("CanvasRenderingContext2D")}}接口的<strong><code>setLineDash()</code></strong>方法在填充线时使用虚线模式。 它使用一组值来指定描述模式的线和间隙的交替长度。</p>

<div class="blockIndicator note">
<p><strong>提示：</strong>如果要切换回至实线模式，将 dash list 设置为一个空数组即可。</p>
</div>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">void <var><em>ctx</em>.setLineDash(segments);</var>
</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt><code>segments</code></dt>
 <dd>一个{{jsxref("Array")}}数组。一组描述交替绘制线段和间距（坐标空间单位）长度的数字。 如果数组元素的数量是奇数， 数组的元素会被复制并重复。例如， <code>[5, 15, 25]</code> 会变成 <code>[5, 15, 25, 5, 15, 25]。</code></dd>
 <dt>
 <h3 id="返回值">返回值</h3>
 </dt>
 <dd>{{jsxref("undefined")}}</dd>
</dl>

<h2 id="示例">示例</h2>

<h3 id="基本示例">基本示例</h3>

<p>这是一段简单的代码片段，使用 <code>setLineDash</code> 方法绘制一条线段。</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">const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

// Dashed line
ctx.beginPath();
ctx.setLineDash([5, 15]);
ctx.moveTo(0, 50);
ctx.lineTo(300, 50);
ctx.stroke();

// Solid line
ctx.beginPath();
ctx.setLineDash([]);
ctx.moveTo(0, 100);
ctx.lineTo(300, 100);
ctx.stroke();
</pre>

<h4 id="结果">结果</h4>

<div class="hidden">
<h6 id="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"&gt;
ctx.setLineDash([5, 15]);
ctx.beginPath();
ctx.moveTo(0,100);
ctx.lineTo(400, 100);
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('基本示例', 700, 360) }}</p>

<h3 id="一些常见的模式">一些常见的模式</h3>

<p>此示例说明了各种常见的线划线模式。</p>

<h4 id="HTML_2">HTML</h4>

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

<h4 id="JavaScript_2">JavaScript</h4>

<p>下面创建的<code>drawDashedLine()</code> 函数使得多个虚线的绘制变得简单。它接收模式数组作为其唯一参数。</p>

<pre class="brush: js">function drawDashedLine(pattern) {
  ctx.beginPath();
  ctx.setLineDash(pattern);
  ctx.moveTo(0, y);
  ctx.lineTo(300, y);
  ctx.stroke();
  y += 20;
}

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
let y = 15;

drawDashedLine([]);
drawDashedLine([1, 1]);
drawDashedLine([10, 10]);
drawDashedLine([20, 5]);
drawDashedLine([15, 3, 3, 3]);
drawDashedLine([20, 3, 3, 3, 3, 3, 3, 3]);
drawDashedLine([12, 3, 3]);  // Equals [12, 3, 3, 12, 3, 3]</pre>

<h4 id="Result">Result</h4>

<p>{{ EmbedLiveSample('一些常见的模式', 700, 180) }}</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-setlinedash", "CanvasRenderingContext2D.setLineDash")}}</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.setLineDash")}}</p>

<h2 id="参见">参见</h2>

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