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<?xml version="1.0"?>
<extension href="WEBGL_compressed_texture_etc/">
<name>WEBGL_compressed_texture_etc</name>
<contact>
<a href="https://www.khronos.org/webgl/public-mailing-list/">WebGL working group</a> (public_webgl 'at' khronos.org)
</contact>
<contributors>
<contributor>Jeff Gilbert, Mozilla</contributor>
<contributor>Members of the WebGL working group</contributor>
</contributors>
<number>29</number>
<depends>
<api version="1.0"/>
</depends>
<overview>
<p>
This extension exposes the compressed texture formats defined as core in the
<a href="http://www.khronos.org/registry/gles/specs/3.0/es_spec_3.0.4.pdf">
OpenGL ES 3.0</a> spec to WebGL. These include the ETC2 and EAC formats, where
ETC2 is a superset of ETC1. ETC1 textures can be loaded using the ETC2 token
value. All of these formats are in the ETC family.
</p>
<p>
Browsers should not advertise this extension when the WebGL implementation, or
graphics driver, supports these formats by decompressing them.
</p>
<features>
<feature>
Compression formats <code>COMPRESSED_R11_EAC</code>,
<code>COMPRESSED_SIGNED_R11_EAC</code>,
<code>COMPRESSED_RG11_EAC</code>,
<code>COMPRESSED_SIGNED_RG11_EAC</code>,
<code>COMPRESSED_RGB8_ETC2</code>,
<code>COMPRESSED_SRGB8_ETC2</code>,
<code>COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2</code>,
<code>COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2</code>,
<code>COMPRESSED_RGBA8_ETC2_EAC</code>,
and <code>COMPRESSED_SRGB8_ALPHA8_ETC2_EAC</code> may be passed to the
<code>compressedTexImage2D</code> and <code>compressedTexSubImage2D</code> entry points. In
WebGL 2.0, they may also be passed to the <code>compressedTexImage3D</code> and
<code>compressedTexSubImage3D</code> entry points with the <code>TEXTURE_2D_ARRAY</code>
target.
</feature>
<feature>
Calling <code>getParameter</code> with the argument <code>COMPRESSED_TEXTURE_FORMATS</code>
will include the formats from this specification.
</feature>
<feature>
For all of the formats, <code>validatedSize</code> (defined for each specific format
below) is validated in the following ways:
<ul>
<li>
<b>WebGL 1.0 and 2.0</b>: if the variant of <code>compressedTexImage*D</code> or
<code>compressedTexSubImage*D</code> taking <code>ArrayBufferView pixels</code> is
called, then the <code>byteLength</code> of the view must be equal to
<code>validatedSize</code>, or an INVALID_VALUE error is generated.
</li>
<li>
<b>WebGL 2.0</b>: if the variant of <code>compressedTexImage*D</code> or
<code>compressedTexSubImage*D</code> taking <code>GLintptr offset</code> is called,
and <code>offset + validatedSize</code> is greater than the size of the bound
<code>PIXEL_UNPACK_BUFFER</code>, an <code>INVALID_OPERATION</code> error is
generated.
</li>
</ul>
<dl>
<dt>COMPRESSED_R11_EAC</dt>
<dt>COMPRESSED_SIGNED_R11_EAC</dt>
<dt>COMPRESSED_RGB8_ETC2</dt>
<dt>COMPRESSED_SRGB8_ETC2</dt>
<dt>COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2</dt>
<dt>COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2</dt>
<dd><p><code>validatedSize</code> is computed in the following way:</p>
<blockquote><code>
floor((width + 3) / 4) * floor((height + 3) / 4) * 8
</code></blockquote>
</dd>
</dl>
<dl>
<dt>COMPRESSED_RG11_EAC</dt>
<dt>COMPRESSED_SIGNED_RG11_EAC</dt>
<dt>COMPRESSED_RGBA8_ETC2_EAC</dt>
<dt>COMPRESSED_SRGB8_ALPHA8_ETC2_EAC</dt>
<dd><p><code>validatedSize</code> is computed in the following way:</p>
<blockquote><code>
floor((width + 3) / 4) * floor((height + 3) / 4) * 16
</code></blockquote>
</dd>
</dl>
</feature>
</features>
</overview>
<idl xml:space="preserve">
[NoInterfaceObject]
interface WEBGL_compressed_texture_etc {
/* Compressed Texture Formats */
const GLenum COMPRESSED_R11_EAC = 0x9270;
const GLenum COMPRESSED_SIGNED_R11_EAC = 0x9271;
const GLenum COMPRESSED_RG11_EAC = 0x9272;
const GLenum COMPRESSED_SIGNED_RG11_EAC = 0x9273;
const GLenum COMPRESSED_RGB8_ETC2 = 0x9274;
const GLenum COMPRESSED_SRGB8_ETC2 = 0x9275;
const GLenum COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2 = 0x9276;
const GLenum COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2 = 0x9277;
const GLenum COMPRESSED_RGBA8_ETC2_EAC = 0x9278;
const GLenum COMPRESSED_SRGB8_ALPHA8_ETC2_EAC = 0x9279;
};
</idl>
<newtok>
<function name="compressedTexImage2D">
<param name="internalformat" type="GLenum"/>
Accepted by the <code>internalformat</code> parameter:
<code>COMPRESSED_R11_EAC</code>,
<code>COMPRESSED_SIGNED_R11_EAC</code>,
<code>COMPRESSED_RG11_EAC</code>,
<code>COMPRESSED_SIGNED_RG11_EAC</code>,
<code>COMPRESSED_RGB8_ETC2</code>,
<code>COMPRESSED_SRGB8_ETC2</code>,
<code>COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2</code>,
<code>COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2</code>,
<code>COMPRESSED_RGBA8_ETC2_EAC</code> or
<code>COMPRESSED_SRGB8_ALPHA8_ETC2_EAC</code>
<br/>
</function>
<function name="compressedTexSubImage2D">
<param name="internalformat" type="GLenum"/>
Accepted by the <code>internalformat</code> parameter:
<code>COMPRESSED_R11_EAC</code>,
<code>COMPRESSED_SIGNED_R11_EAC</code>,
<code>COMPRESSED_RG11_EAC</code>,
<code>COMPRESSED_SIGNED_RG11_EAC</code>,
<code>COMPRESSED_RGB8_ETC2</code>,
<code>COMPRESSED_SRGB8_ETC2</code>,
<code>COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2</code>,
<code>COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2</code>,
<code>COMPRESSED_RGBA8_ETC2_EAC</code> or
<code>COMPRESSED_SRGB8_ALPHA8_ETC2_EAC</code>
<br/>
</function>
</newtok>
<errors>
<error enum="INVALID_VALUE">
The error <code>INVALID_VALUE</code> is generated by <code>compressedTexImage2D</code>,
<code>compressedTexSubImage2D</code>, <code>compressedTexImage3D</code>, and
<code>compressedTexSubImage3D</code> if the variant taking <code>ArrayBufferView pixels</code>
is called and the size restrictions above are not met.
</error>
<error enum="INVALID_OPERATION">
The error <code>INVALID_OPERATION</code> is generated by <code>compressedTexImage2D</code>,
<code>compressedTexSubImage2D</code>, <code>compressedTexImage3D</code>, and
<code>compressedTexSubImage3D</code> if the variant taking <code>GLintptr offset</code> is
called and the size restrictions above are not met.
</error>
</errors>
<history>
<revision date="2013/12/9">
<change>Initial revision.</change>
</revision>
<revision date="2014/07/15">
<change>Added NoInterfaceObject extended attribute.</change>
</revision>
<revision date="2014/12/12">
<change>COMPRESSED_RGB_ETC2 should be COMPRESSED_RGB8_ETC2.</change>
<change>Remove unnecessary language.</change>
</revision>
<revision date="2015/01/31">
<change>Moved to draft.</change>
<change>Added issue questions.</change>
<change>Formalized the newtok and error codes.</change>
</revision>
<revision date="2016/09/16">
<change>Renamed to WEBGL_compressed_texture_es3_0.</change>
</revision>
<revision date="2016/09/21">
<change>Clarifications to the supported formats on suggestion from Mark Callow.</change>
</revision>
<revision date="2016/09/30">
<change>Addressed issues regarding 3D entry points, description of interation with WebGL 2.0,
and generation of INVALID_OPERATION and INVALID_VALUE errors. Added note that browsers should
not advertise this extension if these compressed texture formats are decompressed. Renamed to
WEBGL_compressed_texture_etc after further discussion. Promoted to community
approved.</change>
</revision>
</history>
</extension>
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