APPLE_texture_format_BGRA8888

GL_APPLE_texture_format_BGRA8888

Benj Lipchak, Apple (lipchak 'at' apple.com)

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Complete.

Last Modified Date: June 26, 2013
Revision: 3

OpenGL ES Extension #79

Written based on the wording of the OpenGL ES 1.1 specification.
There are interactions with OpenGL ES 3.0 or EXT_texture_storage.

This extension introduces BGRA_EXT as an acceptable external format.  
This avoids byte swizzling when loading RGBA internal format
textures, which may be stored in BGRA order internally.

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Accepted by the <format> parameters of TexImage2D and TexSubImage2D:

    GL_BGRA_EXT                                 0x80E1

Accepted by the <internalformat> parameters of TexStorage2D and 
TexStorage3D:

    GL_BGRA8_EXT                                0x93A1

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Section 3.6.2, add the following row to Table 3.3:

    Format Name    Element Meaning and Order    Target Buffer
    -----------    -------------------------    -------------
    BGRA_EXT       B, G, R, A                   Color

Section 3.6.2, add the following row to Table 3.4:

    Format      Type             Bytes per Pixel
    --------    -------------    ---------------
    BGRA_EXT    UNSIGNED_BYTE    4

Section 3.7.1, change the 4th paragraph to loosen the requirement that
<internalformat> must match <format> for the case of BGRA_EXT format, which
must have an RGBA internal format.  In this case we do not generate the
error INVALID_OPERATION.

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When the GL is OpenGL ES 3.0, the following table entry is added to
Table 3.2:

    Format    Type           External Bytes per Pixel  Internal Format
    --------  -------------  ------------------------  ---------------
    BGRA_EXT  UNSIGNED_BYTE  4                         BGRA8_EXT

When the GL is OpenGL ES 3.0, BGRA8_EXT is also added to the Texture-only 
color formats list in the Required Texture Formats subsection of section 
3.8.3.

If the GL is not OpenGL ES 3.0 and the EXT_texture_storage extension is not
present, omit references to BGRA8_EXT and TexStorage*.

Note that despite TexStorage* being defined in terms of TexImage*, 
BGRA8_EXT is not accepted as an <internalformat> parameter to TexImage* 
when the GL is OpenGL ES 3.0.

Details of how this extension interacts with EXT_texture_storage when the 
GL is a version of OpenGL earlier than 3.0 can be found in the 
EXT_texture_storage spec.

INVALID_ENUM is generated by TexImage2D if <internalformat> is BGRA_EXT.

INVALID_OPERATION is generated by TexImage2D if <format> is BGRA_EXT and
<internalformat> is not RGBA.

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#3  06/26/2013    Benj Lipchak     Add ES3 interactions
#2  10/27/2009    Benj Lipchak     Add EXT suffix to BGRA token
#1  05/14/2009    Benj Lipchak     First draft