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

<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.quadraticCurveTo()</code></strong> 是 Canvas 2D API 新增二次贝塞尔曲线路径的方法。它需要2个点。 第一个点是控制点，第二个点是终点。 起始点是当前路径最新的点，当创建二次贝赛尔曲线之前，可以使用 <code>moveTo()</code> 方法进行改变。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">void <var><em>ctx</em>.quadraticCurveTo(cpx, cpy, x, y);</var>
</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt><code>cpx</code></dt>
 <dd>控制点的 x 轴坐标。</dd>
 <dt><code>cpy</code></dt>
 <dd>控制点的 y 轴坐标。</dd>
 <dt><code>x</code></dt>
 <dd>终点的 x 轴坐标。</dd>
 <dt><code>y</code></dt>
 <dd>终点的 y 轴坐标。</dd>
</dl>

<h2 id="示例">示例</h2>

<h3 id="quadraticCurveTo_如何工作"><code>quadraticCurveTo</code> 如何工作</h3>

<p>这是一段绘制二次贝赛尔曲线的简单的代码片段。 <span style="color: red;">控制点是红色</span>，<span style="color: blue;">起点和终点是蓝色。</span></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');

// Quadratic Bézier curve
ctx.beginPath();
ctx.moveTo(50, 20);
ctx.quadraticCurveTo(230, 30, 50, 100);
ctx.stroke();

// Start and end points
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.arc(50, 20, 5, 0, 2 * Math.PI);   // Start point
ctx.arc(50, 100, 5, 0, 2 * Math.PI);  // End point
ctx.fill();

// Control point
ctx.fillStyle = 'red';
ctx.beginPath();
ctx.arc(230, 30, 5, 0, 2 * Math.PI);
ctx.fill();</pre>

<div class="hidden">
<h2 id="Using_the_quadraticCurveTo_method">Using_the_quadraticCurveTo_method</h2>

<h3 id="HTML_2">HTML</h3>

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

<h3 id="JavaScript_2">JavaScript</h3>

<pre class="brush: js">const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

// Quadratic Bézier curve
ctx.beginPath();
ctx.moveTo(50, 20);
ctx.quadraticCurveTo(230, 30, 50, 100);
ctx.stroke();

// Start and end points
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.arc(50, 20, 5, 0, 2 * Math.PI);   // Start point
ctx.arc(50, 100, 5, 0, 2 * Math.PI);  // End point
ctx.fill();

// Control point
ctx.fillStyle = 'red';
ctx.beginPath();
ctx.arc(230, 30, 5, 0, 2 * Math.PI);
ctx.fill();</pre>
</div>

<p>{{ EmbedLiveSample('Using_the_quadraticCurveTo_method', 315, 165) }}</p>

<h3 id="简单的二次曲线">简单的二次曲线</h3>

<p>此示例使用<code>quadraticCurveTo()</code>绘制了简单的二次Bézier曲线。</p>

<h4 id="HTML_3">HTML</h4>

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

<h4 id="JavaScript_3">JavaScript</h4>

<p>曲线从<code>moveTo()</code>指定的点开始: (20, 110)。 控制点位于(230, 150)。 曲线在(250, 20)处结束。</p>

<pre class="brush: js">const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

ctx.beginPath();
ctx.moveTo(20, 110);
ctx.quadraticCurveTo(230, 150, 250, 20);
ctx.stroke();
</pre>

<h4 id="结果">结果</h4>

<div class="hidden">
<h2 id="Trying_the_quadraticCurveTo_parameters">Trying_the_quadraticCurveTo_parameters</h2>

<h3 id="HTML_4">HTML</h3>

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

<h3 id="JavaScript_4">JavaScript</h3>

<pre class="brush: js">const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

ctx.beginPath();
ctx.moveTo(20, 110);
ctx.quadraticCurveTo(230, 150, 250, 20);
ctx.stroke();
</pre>
</div>

<div class="hidden">
<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.beginPath();
ctx.moveTo(50,20);
ctx.quadraticCurveTo(230, 30, 50, 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('Trying_the_quadraticCurveTo_parameters', 700, 360) }}</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-quadraticcurveto", "CanvasRenderingContext2D.quadraticCurveTo")}}</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.quadraticCurveTo")}}</p>

<ul>
 <li>接口定义，{{domxref("CanvasRenderingContext2D")}}</li>
 <li><a href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve">WikiPedia article on Bézier curves</a>.</li>
</ul>