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---
title: CanvasRenderingContext2D.beginPath()
slug: Web/API/CanvasRenderingContext2D/beginPath
translation_of: Web/API/CanvasRenderingContext2D/beginPath
---
<div>{{APIRef}}</div>
<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.beginPath()</code></strong> 是 Canvas 2D API 通过清空子路径列表开始一个新路径的方法。 当你想创建一个新的路径时，调用此方法。</p>
<h2 id="语法">语法</h2>
<pre class="syntaxbox">void <var><em>ctx</em>.beginPath();</var>
</pre>
<h2 id="示例">示例</h2>
<h3 id="使用_beginPath_方法">使用 <code>beginPath</code> 方法</h3>
<p>这是一段受用 <code>beginPath</code> 方法的简单的代码片段。</p>
<h4 id="HTML">HTML</h4>
<pre class="brush: html"><canvas id="canvas"></canvas>
</pre>
<h4 id="JavaScript">JavaScript</h4>
<pre class="brush: js; highlight:[5,12]">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
// First path
ctx.beginPath();
ctx.strokeStyle = 'blue';
ctx.moveTo(20,20);
ctx.lineTo(200,20);
ctx.stroke();
// Second path
ctx.beginPath();
ctx.strokeStyle = 'green';
ctx.moveTo(20,20);
ctx.lineTo(120,120);
ctx.stroke();
</pre>
<p>修改下面的代码并在线查看 canvas 的变化：</p>
<div style="display: none;">
<h6 id="Playable_code">Playable code</h6>
<pre class="brush: html"><canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
<input id="edit" type="button" value="Edit" />
<input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code" style="height:200px">
// First path
ctx.beginPath();
ctx.strokeStyle = 'blue';
ctx.moveTo(20,20);
ctx.lineTo(200,20);
ctx.stroke();
// Second path
ctx.beginPath();
ctx.strokeStyle = 'green';
ctx.moveTo(20,20);
ctx.lineTo(120, 120);
ctx.stroke();</textarea>
</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, 460) }}</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-beginpath", "CanvasRenderingContext2D.beginPath")}}</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>
<h2 id="参见">参见</h2>
<ul>
<li>接口定义， {{domxref("CanvasRenderingContext2D")}}</li>
<li>{{domxref("CanvasRenderingContext2D.closePath()")}}</li>
</ul>
|
