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<?xml version="1.0"?>
<extension href="WEBGL_compressed_texture_etc1/">
<name>WEBGL_compressed_texture_etc1</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>24</number>
<depends>
<api version="1.0"/>
</depends>
<overview>
<p>
This extension exposes the compressed texture format defined in the
<a href="http://www.khronos.org/registry/gles/extensions/OES/OES_compressed_ETC1_RGB8_texture.txt">
OES_compressed_ETC1_RGB8_texture</a> OpenGL ES extension to WebGL.
</p>
<features>
<feature>
Compression format <code>COMPRESSED_RGB_ETC1_WEBGL</code> may be passed to
the <code>compressedTexImage2D</code> entry point.
This format correspond to the format defined in the OES_compressed_ETC1_RGB8_texture OpenGL ES
extension. Although the enum name is changed, the numeric value is 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_ETC1_WEBGL</td>
<td>ETC1_RGB8_OES</td>
<td>0x8D64</td>
</tr>
</table>
</feature>
<feature>
Calling <code>getParameter</code> with the argument <code>COMPRESSED_TEXTURE_FORMATS</code>
will include the format from this specification.
</feature>
<feature>
<p>The following format-specific restrictions must be enforced:</p>
<dl>
<dt>COMPRESSED_RGB_ETC1_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>
</dl>
</feature>
</features>
</overview>
<idl xml:space="preserve">
[NoInterfaceObject]
interface WEBGL_compressed_texture_etc1 {
/* Compressed Texture Format */
const GLenum COMPRESSED_RGB_ETC1_WEBGL = 0x8D64;
};
</idl>
<history>
<revision date="2012/02/23">
<change>Initial revision.</change>
</revision>
<revision date="2013/07/03">
<change>Clarified that length of ArrayBufferView is actually byteLength.</change>
</revision>
<revision date="2013/11/27">
<change>Moved to draft status.</change>
</revision>
<revision date="2013/12/03">
<change>Assigned extension number 24 to WEBGL_compressed_texture_etc1 extension.</change>
</revision>
<revision date="2014/03/07">
<change>Remove ability to use the format with compressedTexSubImage2D, as per the GLES extension spec.</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>
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