---
title: WebGLRenderingContext.isEnabled()
slug: Web/API/WebGLRenderingContext/isEnabled
translation_of: Web/API/WebGLRenderingContext/isEnabled
---
<div>{{APIRef("WebGL")}}</div>

<p><strong><code>WebGLRenderingContext.isEnabled()</code></strong> 是 <a href="/en-US/docs/Web/API/WebGL_API">WebGL API</a> 方法之一，用来检测给定的 WebGL 功能项在当前上下文是否可用。</p>

<p>默认的，除了 <code>gl.DITHER</code>，所有的功能项都是未启用的。</p>

<h2 id="句法">句法</h2>

<pre class="syntaxbox">void <var>gl</var>.isEnabled(<var>cap</var>);
</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt><code>cap</code></dt>
 <dd>{{domxref("GLenum")}} 指定待检测的 WebGL 功能项。可能的值有：</dd>
 <dd>
 <table class="standard-table">
  <thead>
   <tr>
    <th scope="col">Constant</th>
    <th scope="col">Description</th>
   </tr>
  </thead>
  <tbody>
   <tr>
    <td><code>gl.BLEND</code></td>
    <td>Blending of the computed fragment color values. See {{domxref("WebGLRenderingContext.blendFunc()")}}.</td>
   </tr>
   <tr>
    <td><code>gl.CULL_FACE</code></td>
    <td>Culling of polygons. See {{domxref("WebGLRenderingContext.cullFace()")}}.</td>
   </tr>
   <tr>
    <td><code>gl.DEPTH_TEST</code></td>
    <td>Depth comparisons and updates to the depth buffer. See {{domxref("WebGLRenderingContext.depthFunc()")}}.</td>
   </tr>
   <tr>
    <td><code>gl.DITHER</code></td>
    <td>Dithering of color components before they get written to the color buffer.</td>
   </tr>
   <tr>
    <td><code>gl.POLYGON_OFFSET_FILL</code></td>
    <td>Adding an offset to depth values of polygon's fragments. See {{domxref("WebGLRenderingContext.polygonOffset()")}}.</td>
   </tr>
   <tr>
    <td><code>gl.SAMPLE_ALPHA_TO_COVERAGE</code></td>
    <td>Computation of a temporary coverage value determined by the alpha value.</td>
   </tr>
   <tr>
    <td><code>gl.SAMPLE_COVERAGE</code></td>
    <td>ANDing the fragment's coverage with the temporary coverage value. See {{domxref("WebGLRenderingContext.sampleCoverage()")}}.</td>
   </tr>
   <tr>
    <td><code>gl.SCISSOR_TEST</code></td>
    <td>Scissor test that discards fragments that are outside of the scissor rectangle. See {{domxref("WebGLRenderingContext.scissor()")}}.</td>
   </tr>
   <tr>
    <td><code>gl.STENCIL_TEST</code></td>
    <td>Stencil testing and updates to the stencil buffer. See {{domxref("WebGLRenderingContext.stencilFunc()")}}.</td>
   </tr>
  </tbody>
 </table>
 当使用 {{domxref("WebGL2RenderingContext", "WebGL 2 context", "", 1)}} 的时候，下列附加的值也是可选用的。

 <table class="standard-table">
  <thead>
   <tr>
    <th scope="col">Constant</th>
    <th scope="col">Description</th>
   </tr>
  </thead>
  <tbody>
   <tr>
    <td><code>gl.RASTERIZER_DISCARD</code></td>
    <td>Primitives are discarded immediately before the rasterization stage, but after the optional transform feedback stage. <code>gl.clear()</code> commands are ignored.</td>
   </tr>
  </tbody>
 </table>
 </dd>
</dl>

<h3 id="返回值">返回值</h3>

<p>{{domxref("GLboolean")}} 指示能力项 <em>cap </em>可用 (<code>true</code>)，不可用 (<code>false</code>)。</p>

<h2 id="示例">示例</h2>

<pre class="brush: js">gl.isEnabled(gl.STENCIL_TEST);
// false
</pre>

<p>启用或停用给定的能力项，使用 {{domxref("WebGLRenderingContext.enable()")}} 方法和 {{domxref("WebGLRenderingContext.disable()")}} 方法：</p>

<pre class="brush: js">gl.enable(gl.STENCIL_TEST);
gl.disable(gl.STENCIL_TEST);
</pre>

<h2 id="规范">规范</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('WebGL', "#5.14.3", "isEnabled")}}</td>
   <td>{{Spec2('WebGL')}}</td>
   <td>Initial definition for WebGL.</td>
  </tr>
  <tr>
   <td>{{SpecName('OpenGL ES 2.0', "glIsEnabled.xml", "glIsEnabled")}}</td>
   <td>{{Spec2('OpenGL ES 2.0')}}</td>
   <td>Man page of the (similar) OpenGL ES 2.0 API.</td>
  </tr>
  <tr>
   <td>{{SpecName('WebGL2', "#3.7.2", "isEnabled")}}</td>
   <td>{{Spec2('WebGL2')}}</td>
   <td>Updated definition for WebGL 2.</td>
  </tr>
  <tr>
   <td>{{SpecName('OpenGL ES 3.0', "glIsEnabled.xhtml", "glIsEnabled")}}</td>
   <td>{{Spec2('OpenGL ES 3.0')}}</td>
   <td>Man page of the (similar) OpenGL ES 3.0 API.</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<div>{{CompatibilityTable}}</div>

<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>{{CompatChrome("9")}}</td>
   <td>{{CompatGeckoDesktop("2.0")}}</td>
   <td>{{CompatIE("11")}}</td>
   <td>{{CompatOpera("12")}}</td>
   <td>{{CompatSafari("5.1")}}</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>{{CompatUnknown}}</td>
   <td>25</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>12</td>
   <td>8.1</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="另见">另见</h2>

<ul>
 <li>{{domxref("WebGLRenderingContext.enable()")}}</li>
 <li>{{domxref("WebGLRenderingContext.disable()")}}</li>
</ul>