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<?xml version="1.0"?>
<rejected href="rejected/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>
<revision date="2018/04/25">
<change>Moved to rejected status at Khronos Montreal face-to-face meeting.</change>
</revision>
</history>
</rejected>
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