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<?xml version="1.0"?>
<extension href="WEBGL_compressed_texture_pvrtc/">
<name>WEBGL_compressed_texture_pvrtc</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>13</number>
<depends>
<api version="1.0"/>
</depends>
<overview>
<p>
This extension exposes the compressed texture formats defined in the
IMG_texture_compression_pvrtc</a> OpenGL extension to WebGL.
</p>
<features>
<feature>
Compression formats <code>COMPRESSED_RGB_PVRTC_4BPPV1_IMG</code>,
<code>COMPRESSED_RGB_PVRTC_2BPPV1_IMG</code>, <code>COMPRESSED_RGBA_PVRTC_4BPPV1_IMG</code>, and
<code>COMPRESSED_RGBA_PVRTC_2BPPV1_IMG</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 apply to all of the formats described
by this extension:
</p>
<p>In <code>compressedTexImage2D</code>, the <code>width</code> and <code>height</code>
parameters must be powers of two. Otherwise, an INVALID_VALUE error is generated.
</p>
<p>
In <code>compressedTexSubImage2D</code>, the <code>width</code> and <code>height</code>
parameters must be equal to the current values of the existing texture image, and the
<code>xoffset</code> and <code>yoffset</code> parameters must be zero.
Otherwise, an INVALID_VALUE error is generated.
</p>
</feature>
<feature>
<p>The following format-specific restrictions must also be enforced:</p>
<dl>
<dt>COMPRESSED_RGB_PVRTC_4BPPV1_IMG</dt>
<dt>COMPRESSED_RGBA_PVRTC_4BPPV1_IMG</dt>
<dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
either <code>compressedTexImage2D</code> or <code>compressedTexSubImage2D</code> must be
equal to the following number of bytes:</p>
<blockquote><code>
max(width, 8) * max(height, 8) / 2
</code></blockquote>
<p>If it is not, an <code>INVALID_VALUE</code> error is generated.</p>
</dd>
<dt>COMPRESSED_RGB_PVRTC_2BPPV1_IMG</dt>
<dt>COMPRESSED_RGBA_PVRTC_2BPPV1_IMG</dt>
<dd><p>The <code>byteLength</code> of the ArrayBufferView, <code>pixels</code>, passed to
either <code>compressedTexImage2D</code> or <code>compressedTexSubImage2D</code> must be
equal to the following number of bytes:</p>
<blockquote><code>
max(width, 16) * max(height, 8) / 4
</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_pvrtc {
/* Compressed Texture Formats */
const GLenum COMPRESSED_RGB_PVRTC_4BPPV1_IMG = 0x8C00;
const GLenum COMPRESSED_RGB_PVRTC_2BPPV1_IMG = 0x8C01;
const GLenum COMPRESSED_RGBA_PVRTC_4BPPV1_IMG = 0x8C02;
const GLenum COMPRESSED_RGBA_PVRTC_2BPPV1_IMG = 0x8C03;
};
</idl>
<history>
<revision date="2012/08/07">
<change>Initial revision.</change>
</revision>
<revision date="2013/07/03">
<change>Clarified that length of ArrayBufferView is actually byteLength.</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>