Revision 1017866 of WEBGL_compressed_texture_s3tc

<div>{{APIRef("WebGL")}}</div>

<p>The <code><strong>WEBGL_compressed_texture_s3tc</strong></code> extension is part of the <a href="/en-US/docs/Web/API/WebGL_API">WebGL API</a> and exposes four <a href="https://en.wikipedia.org/wiki/S3_Texture_Compression">S3TC compressed texture formats</a>.</p>

<p>Compressed textures reduce the amount of memory needed to store a texture on the GPU, allowing for higher resolution textures or more of the same resolution textures.</p>

<p>WebGL extensions are available using the {{domxref("WebGLRenderingContext.getExtension()")}} method. For more information, see also <a href="/en-US/docs/Web/API/WebGL_API/Using_Extensions">Using Extensions</a> in the <a href="/en-US/docs/Web/API/WebGL_API/Tutorial">WebGL tutorial</a>.</p>

<div class="note">
<p><strong>Availability:</strong> This extension is available to both, {{domxref("WebGLRenderingContext", "WebGL1", "", 1)}} and {{domxref("WebGL2RenderingContext", "WebGL2", "", 1)}} contexts.</p>
</div>

<h2 id="Constants">Constants</h2>

<p>The compressed texture formats are exposed by four constants and can be used in two functions: {{domxref("WebGLRenderingContext.compressedTexImage2D", "compressedTexImage2D()")}} and {{domxref("WebGLRenderingContext.compressedTexSubImage2D", "compressedTexSubImage2D()")}}.</p>

<dl>
 <dt><code>ext.COMPRESSED_RGB_S3TC_DXT1_EXT</code></dt>
 <dd>A DXT1-compressed image in an RGB image format.</dd>
 <dt><code>ext.COMPRESSED_RGBA_S3TC_DXT1_EXT</code></dt>
 <dd>A DXT1-compressed image in an RGB image format with a simple on/off alpha value.</dd>
 <dt><code>ext.COMPRESSED_RGBA_S3TC_DXT3_EXT</code></dt>
 <dd>A DXT3-compressed image in an RGBA image format. Compared to a 32-bit RGBA texture, it offers 4:1 compression.</dd>
 <dt><code>ext.COMPRESSED_RGBA_S3TC_DXT5_EXT</code></dt>
 <dd>A DXT5-compressed image in an RGBA image format. It also provides a 4:1 compression, but differs to the DXT3 compression in how the alpha compression is done.</dd>
</dl>

<h2 id="Examples">Examples</h2>

<pre class="brush:js">
var ext = (
  gl.getExtension("WEBGL_compressed_texture_s3tc") ||
  gl.getExtension("MOZ_WEBGL_compressed_texture_s3tc") ||
  gl.getExtension("WEBKIT_WEBGL_compressed_texture_s3tc")
);

var texture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, texture);

gl.compressedTexImage2D(gl.TEXTURE_2D, 0, ext.COMPRESSED_RGBA_S3TC_DXT5_EXT, 512, 512, 0, textureData); 

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);</pre>

<h2 id="Specifications">Specifications</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_compressed_texture_s3tc', "", "WEBGL_compressed_texture_s3tc")}}</td>
   <td>{{Spec2('WEBGL_compressed_texture_s3tc')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</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>{{CompatUnknown}}</td>
   <td>{{CompatGeckoDesktop("22.0")}} [2]</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</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>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1] This extension was prefixed with <code>MOZ_</code> from version 15 to version 21.</p>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="https://www.opengl.org/wiki/S3_Texture_Compression">S3 Texture Compression – OpenGL wiki</a></li>
 <li>{{domxref("WebGLRenderingContext.getExtension()")}}</li>
 <li>{{domxref("WebGLRenderingContext.compressedTexImage2D()")}}</li>
 <li>{{domxref("WebGLRenderingContext.compressedTexSubImage2D()")}}</li>
 <li>{{domxref("WebGLRenderingContext.getParameter()")}}</li>
</ul>