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<?xml version="1.0"?>
<draft href="EXT_texture_compression_rgtc/">
<name>EXT_texture_compression_rgtc</name>
<contact>
<a href="https://www.khronos.org/webgl/public-mailing-list/">WebGL working group</a> (public_webgl 'at' khronos.org)
</contact>
<contributors>
<contributor>Olli Etuaho, NVIDIA</contributor>
<contributor>Members of the WebGL working group</contributor>
</contributors>
<number>39</number>
<depends>
<api version="1.0"/>
</depends>
<overview>
<p>
This extension exposes the compressed texture format defined in the
<a href="https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_texture_compression_rgtc.txt">
EXT_texture_compression_rgtc</a> OpenGL extension to WebGL. Consult that extension
specification for behavioral definitions, including error behaviors.
</p>
<p>
Updates of partial tiles detailed in the "Implementation Note" section of the
EXT_texture_compression_rgtc specification must be supported in an implementation of this
WebGL extension.
</p>
<features>
<feature>
Compression formats <code>COMPRESSED_RED_RGTC1_EXT</code>,
<code>COMPRESSED_SIGNED_RED_RGTC1_EXT</code>,
<code>COMPRESSED_RED_GREEN_RGTC2_EXT</code>,
and <code>COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT</code> may be passed to
the <code>compressedTexImage2D</code> and <code>compressedTexSubImage2D</code> entry points.
</feature>
<feature>
Calling <code>getParameter</code> with the argument <code>COMPRESSED_TEXTURE_FORMATS</code>
will include the formats from this specification.
</feature>
<feature>
<p>The following format-specific restrictions must be enforced:</p>
<dl>
<dt>COMPRESSED_RED_RGTC1_EXT</dt>
<dt>COMPRESSED_SIGNED_RED_RGTC1_EXT</dt>
<dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
<code>compressedTexImage2D</code> or <code>compressedTexSubImage2D</code> must be equal to the following number of bytes:</p>
<blockquote><code>
ceil(width / 4) * ceil(height / 4) * 8
</code></blockquote>
<p>If it is not, an <code>INVALID_VALUE</code> error is generated.</p>
</dd>
<dt>COMPRESSED_RED_GREEN_RGTC2_EXT</dt>
<dt>COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT</dt>
<dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
<code>compressedTexImage2D</code> or <code>compressedTexSubImage2D</code> must be equal to the following number of bytes:</p>
<blockquote><code>
ceil(width / 4) * ceil(height / 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 EXT_texture_compression_rgtc {
const GLenum COMPRESSED_RED_RGTC1_EXT = 0x8DBB;
const GLenum COMPRESSED_SIGNED_RED_RGTC1_EXT = 0x8DBC;
const GLenum COMPRESSED_RED_GREEN_RGTC2_EXT = 0x8DBD;
const GLenum COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT = 0x8DBE;
};
</idl>
<newtok>
<function name="compressedTexImage2D">
<param name="internalformat" type="GLenum"/>
Accepted by the <code>internalformat</code> parameter:
<code>COMPRESSED_RED_RGTC1_EXT</code>,
<code>COMPRESSED_SIGNED_RED_RGTC1_EXT</code>,
<code>COMPRESSED_RED_GREEN_RGTC2_EXT</code>,
<code>COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT</code>
<br/>
</function>
<function name="compressedTexSubImage2D">
<param name="internalformat" type="GLenum"/>
Accepted by the <code>internalformat</code> parameter:
<code>COMPRESSED_RED_RGTC1_EXT</code>,
<code>COMPRESSED_SIGNED_RED_RGTC1_EXT</code>,
<code>COMPRESSED_RED_GREEN_RGTC2_EXT</code>,
<code>COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT</code>
<br/>
</function>
</newtok>
<errors>
<error enum="INVALID_VALUE">
The error <code>INVALID_VALUE</code> is generated by <code>compressedTexImage2D</code> and
<code>compressedTexSubImage2D</code> if the <code>internalformat</code> parameter is
<code>COMPRESSED_RED_RGTC1_EXT</code> or <code>COMPRESSED_SIGNED_RED_RGTC1_EXT</code>
and the byteLength of the ArrayBufferView is not:
<blockquote><code>
ceil(width / 4) * ceil(height / 4) * 8
</code></blockquote>
</error>
<error enum="INVALID_VALUE">
The error <code>INVALID_VALUE</code> is generated by <code>compressedTexImage2D</code> and
<code>compressedTexSubImage2D</code> if the <code>internalformat</code> parameter is
<code>COMPRESSED_RED_GREEN_RGTC2_EXT</code> or <code>COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT</code>
and the byteLength of the ArrayBufferView is not:
<blockquote><code>
ceil(width / 4) * ceil(height / 4) * 16
</code></blockquote>
</error>
</errors>
<history>
<revision date="2018/09/26">
<change>Initial revision.</change>
</revision>
<revision date="2018/09/26">
<change>Rename to EXT_texture_compression_rgtc from WEBGL_compressed_texture_rgtc</change>
</revision>
</history>
</draft>
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