khronos_api 2.2.0

The Khronos XML API Registry, exposed as byte string constants.
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<?xml version="1.0"?>

<extension href="WEBGL_compressed_texture_atc/">
  <name>WEBGL_compressed_texture_atc</name>
  <contact>
    <a href="https://www.khronos.org/webgl/public-mailing-list/">WebGL working group</a> (public_webgl 'at' khronos.org)
  </contact>
  <contributors>
    <contributor>Members of the WebGL working group</contributor>
  </contributors>
  <number>12</number>
  <depends>
    <api version="1.0"/>
  </depends>
  <overview>
    <p>
      This extension exposes the compressed texture formats defined in the 
      <a href="http://www.khronos.org/registry/gles/extensions/AMD/AMD_compressed_ATC_texture.txt">
      AMD_compressed_ATC_texture</a> OpenGL extension to WebGL.
    </p>
    <features>
      <feature>
        Compression formats <code>COMPRESSED_RGB_ATC_WEBGL</code>,
        <code>COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL</code>, and
        <code>COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL</code> may be passed to
        the <code>compressedTexImage2D</code> and <code>compressedTexSubImage2D</code> entry points.

        These formats correspond to the 3 formats defined in the AMD_compressed_ATC_texture OpenGL
        extension. Although the enum names are changed, their numeric values are the same. The correspondence
        is given by this table:
        <table>
          <tr>
            <th>WebGL format enum</th>
            <th>OpenGL format enum</th>
            <th>Numeric value</th>
          </tr>
          <tr>
            <td>COMPRESSED_RGB_ATC_WEBGL</td>
            <td>ATC_RGB_AMD</td>
            <td>0x8C92</td>
          </tr>
          <tr>
            <td>COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL</td>
            <td>ATC_RGBA_EXPLICIT_ALPHA_AMD</td>
            <td>0x8C93</td>
          </tr>
          <tr>
            <td>COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL</td>
            <td>ATC_RGBA_INTERPOLATED_ALPHA_AMD</td>
            <td>0x87EE</td>
          </tr>
        </table>
      </feature>
      <feature>
        Calling <code>getParameter</code> with the argument <code>COMPRESSED_TEXTURE_FORMATS</code>
        will include the 3 formats from this specification.
      </feature>
      <feature>
        <p>The following format-specific restrictions must be enforced:</p>
        <dl>
          <dt>COMPRESSED_RGB_ATC_WEBGL</dt>
          <dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
          <code>compressedTexImage2D</code>, must be equal to the following number of bytes:</p>
          <blockquote><code>
            floor((width + 3) / 4) * floor((height + 3) / 4) * 8
          </code></blockquote>
          <p>If it is not, an <code>INVALID_VALUE</code> error is generated.</p>
          </dd>

          <dt>COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL</dt>
          <dt>COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL</dt>
          <dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
          <code>compressedTexImage2D</code>, must be equal to the following number of bytes:</p>
          <blockquote><code>
            floor((width + 3) / 4) * floor((height + 3) / 4) * 16
          </code></blockquote>
          <p>If it is not, an <code>INVALID_VALUE</code> error is generated.</p>
          </dd>
        </dl>
      </feature>
    </features>
  </overview>
  <idl xml:space="preserve">
[NoInterfaceObject]
interface WEBGL_compressed_texture_atc {
    /* Compressed Texture Formats */
    const GLenum COMPRESSED_RGB_ATC_WEBGL                     = 0x8C92;
    const GLenum COMPRESSED_RGBA_ATC_EXPLICIT_ALPHA_WEBGL     = 0x8C93;
    const GLenum COMPRESSED_RGBA_ATC_INTERPOLATED_ALPHA_WEBGL = 0x87EE;
};
  </idl>
  <history>
    <revision date="2012/09/11">
      <change>Initial revision.</change>
    </revision>
    <revision date="2013/07/03">
      <change>Clarified that length of ArrayBufferView is actually byteLength.</change>
    </revision>
    <revision date="2014/04/17">
      <change>Removed reference to compressedTexSubImage2D. This format can only be used with compressedTexImage2D.</change>
    </revision>
    <revision date="2014/06/27">
      <change>Moved to community approved after discussion on public_webgl list.</change>
    </revision>
    <revision date="2014/07/15">
      <change>Added NoInterfaceObject extended attribute.</change>
    </revision>
  </history>
</extension>