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---
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"><canvas id="canvas"></canvas>
</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"><canvas id="canvas"></canvas>
</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"><canvas id="canvas"></canvas>
</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"><canvas id="canvas"></canvas>
</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 style="display: none;">
<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">
ctx.beginPath();
ctx.moveTo(50,20);
ctx.quadraticCurveTo(230, 30, 50, 100);
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('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>
<div class="hidden">
<p>此页面上的兼容性表是根据结构化数据生成的。 如果您想提供数据，请查看<a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a>并向我们发送请求请求。</p>
</div>
<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>
|
