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---
title: CanvasRenderingContext2D.rotate()
slug: Web/API/CanvasRenderingContext2D/rotate
tags:
- API
- Canvas
- CanvasRenderingContext2D
- 引用
- 方法
translation_of: Web/API/CanvasRenderingContext2D/rotate
---
<div>{{APIRef}}</div>
<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.rotate()</code></strong> 是 Canvas 2D API 在变换矩阵中增加旋转的方法。角度变量表示一个顺时针旋转角度并且用弧度表示。</p>
<h2 id="语法">语法</h2>
<pre class="syntaxbox">void <var><em>ctx</em>.rotate(angle);</var>
</pre>
<p><img alt="" class="internal" src="https://mdn.mozillademos.org/files/233/Canvas_grid_rotate.png" style="float: right;"></p>
<h3 id="参数">参数</h3>
<dl>
<dt><code>angle</code></dt>
<dd>顺时针旋转的弧度。如果你想通过角度值计算，可以使用公式： <code><em>degree</em> * Math.PI / 180</code> 。</dd>
</dl>
<p>旋转中心点一直是 canvas 的起始点。 如果想改变中心点，我们可以通过 {{domxref("CanvasRenderingContext2D.translate", "translate()")}} 方法移动 canvas 。</p>
<h2 id="示例">示例</h2>
<h3 id="使用_rotate_方法">使用 <code>rotate</code> 方法</h3>
<p>这是一段使用 <code>rotate</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:[4]">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.rotate(45 * Math.PI / 180);
ctx.fillRect(70,0,100,30);
// reset current transformation matrix to the identity matrix
ctx.setTransform(1, 0, 0, 1, 0, 0);
</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">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">
ctx.rotate(45 * Math.PI / 180);
ctx.fillRect(70,0,100,30);
ctx.setTransform(1, 0, 0, 1, 0, 0);</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, 360) }}</p>
<h2 id="规范描述">规范描述</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">规范</th>
<th scope="col">状态</th>
<th scope="col">注释</th>
</tr>
<tr>
<td>{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-rotate", "CanvasRenderingContext2D.rotate")}}</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>
{{Compat("api.CanvasRenderingContext2D.rotate")}}
<h2 id="参见">参见</h2>
<ul>
<li>接口定义， {{domxref("CanvasRenderingContext2D")}}</li>
</ul>
|
