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---
title: CanvasRenderingContext2D.shadowBlur
slug: Web/API/CanvasRenderingContext2D/shadowBlur
translation_of: Web/API/CanvasRenderingContext2D/shadowBlur
---
<div>{{APIRef}}</div>
<p><code><strong>CanvasRenderingContext2D</strong></code><strong><code>.shadowBlur</code></strong> 是 Canvas 2D API 描述模糊效果程度的属性； 它既不对应像素值也不受当前转换矩阵的影响。 默认值是 0。</p>
<h2 id="语法">语法</h2>
<pre class="syntaxbox"><var><em>ctx</em>.shadowBlur = level;</var>
</pre>
<dl>
<dt><code>level</code></dt>
<dd>描述模糊效果程度的，float 类型的值。默认值是 0。 负数、 {{jsxref("Infinity")}} 或者 {{jsxref("NaN")}} 都会被忽略。</dd>
</dl>
<h2 id="示例">示例</h2>
<h3 id="Using_the_shadowBlur_property" name="Using_the_shadowBlur_property">使用 <code>shadowBlur</code> 属性</h3>
<p>这是一段简单的代码片段，使用 <code>shadowblur 属性设置模糊阴影。</code> 注意：只有设置shadowColor属性值为不透明，阴影才会被绘制。</p>
<h4 id="HTML">HTML</h4>
<pre class="brush: html"><canvas id="canvas"></canvas>
</pre>
<h4 id="JavaScript">JavaScript</h4>
<pre class="brush: js">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.shadowColor = "black";
ctx.shadowBlur = 10;
ctx.fillStyle = "white";
ctx.fillRect(10, 10, 100, 100);
</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" name="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.shadowColor = "black";
ctx.shadowBlur = 10;
ctx.fillStyle = "white";
ctx.fillRect(10, 10, 100, 100);</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">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-shadowblur", "CanvasRenderingContext2D.shadowBlur")}}</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.shadowBlur")}}
<h2 id="参见">参见</h2>
<ul>
<li>接口定义， {{domxref("CanvasRenderingContext2D")}}.</li>
</ul>
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