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<?xml version="1.0"?>
<ratified href="WEBGL_compressed_texture_s3tc/">
<name>WEBGL_compressed_texture_s3tc</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>8</number>
<depends>
<api version="1.0"/>
</depends>
<overview>
<p>
This extension exposes the compressed texture formats defined in the
<a href="http://www.opengl.org/registry/specs/EXT/texture_compression_s3tc.txt">
EXT_texture_compression_s3tc</a> OpenGL extension to WebGL.
</p>
<features>
<feature>
Compression formats <code>COMPRESSED_RGB_S3TC_DXT1_EXT</code>,
<code>COMPRESSED_RGBA_S3TC_DXT1_EXT</code>, <code>COMPRESSED_RGBA_S3TC_DXT3_EXT</code>, and
<code>COMPRESSED_RGBA_S3TC_DXT5_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 4 formats from this specification.
</feature>
<feature>
<p>The following format specific restrictions must be enforced:</p>
<dl>
<dt>COMPRESSED_RGB_S3TC_DXT1_EXT</dt>
<dt>COMPRESSED_RGBA_S3TC_DXT1_EXT</dt>
<dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
either <code>compressedTexImage2D</code> or <code>compressedTexSubImage2D</code>
must match the following equation:</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>
<p>When <code>level</code> equals zero <code>width</code> and <code>height</code>
must be a multiple of 4. When <code>level</code> is greater than 0 <code>width</code>
and <code>height</code> must be 0, 1, 2 or a multiple of 4.</p>
<p>
If they are not an <code>INVALID_OPERATION</code> error is generated.
</p>
<p>
For <code>compressedTexSubImage2D</code> <code>xoffset</code> and
<code>yoffset</code> must be a multiple of 4 and
<code>width</code> must be a multiple of 4 or equal to the original
width of the <code>level</code>. <code>height</code> must be a multiple of 4 or
equal to the original height of the <code>level</code>.
If they are not an <code>INVALID_OPERATION</code> error is generated.
</p>
</dd>
<dt>COMPRESSED_RGBA_S3TC_DXT3_EXT</dt>
<dt>COMPRESSED_RGBA_S3TC_DXT5_EXT</dt>
<dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
either <code>compressedTexImage2D</code> or <code>compressedTexSubImage2D</code> must
match the following equation:</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>
<p>When <code>level</code> equals zero <code>width</code> and <code>height</code>
must be a multiple of 4. When <code>level</code> is greater than 0 <code>width</code>
and <code>height</code> must be 0, 1, 2 or a multiple of 4.</p>
<p>
If they are not an <code>INVALID_OPERATION</code> error is generated.
</p>
<p>
For <code>compressedTexSubImage2D</code> <code>xoffset</code> and
<code>yoffset</code> must be a multiple of 4 and
<code>width</code> must be a multiple of 4 or equal to the original
width of the <code>level</code>. <code>height</code> must be a multiple of 4 or
equal to the original height of the <code>level</code>.
If they are not an <code>INVALID_OPERATION</code> error is generated.
</p>
</dd>
</dl>
</feature>
</features>
</overview>
<idl xml:space="preserve">
[NoInterfaceObject]
interface WEBGL_compressed_texture_s3tc {
/* Compressed Texture Formats */
const GLenum COMPRESSED_RGB_S3TC_DXT1_EXT = 0x83F0;
const GLenum COMPRESSED_RGBA_S3TC_DXT1_EXT = 0x83F1;
const GLenum COMPRESSED_RGBA_S3TC_DXT3_EXT = 0x83F2;
const GLenum COMPRESSED_RGBA_S3TC_DXT5_EXT = 0x83F3;
};
</idl>
<history>
<revision date="2012/01/25">
<change>Initial revision.</change>
</revision>
<revision date="2013/01/26">
<change>Moved from draft to community approved status</change>
</revision>
<revision date="2013/05/15">
<change>Ratified by Khronos Board of Promoters.</change>
</revision>
<revision date="2013/07/03">
<change>Clarified that length of ArrayBufferView is actually byteLength.</change>
</revision>
<revision date="2014/07/15">
<change>Added NoInterfaceObject extended attribute.</change>
</revision>
</history>
</ratified>
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