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Name
MESA_ycbcr_texture
Name Strings
GL_MESA_ycbcr_texture
Contact
Brian Paul, Tungsten Graphics, Inc. (brian.paul 'at' tungstengraphics.com)
Keith Whitwell, Tungsten Graphics, Inc. (keith 'at' tungstengraphics.com)
Status
Shipping (Mesa 4.0.4 and later)
Version
1.0
Number
TBD
Dependencies
OpenGL 1.0 or later is required
This extensions is written against the OpenGL 1.4 Specification.
NV_texture_rectangle effects the definition of this extension.
Overview
This extension supports texture images stored in the YCbCr format.
There is no support for converting YCbCr images to RGB or vice versa
during pixel transfer. The texture's YCbCr colors are converted to
RGB during texture sampling, after-which, all the usual per-fragment
operations take place. Only 2D texture images are supported (not
glDrawPixels, glReadPixels, etc).
A YCbCr pixel (texel) is a 16-bit unsigned short with two components.
The first component is luminance (Y). For pixels in even-numbered
image columns, the second component is Cb. For pixels in odd-numbered
image columns, the second component is Cr. If one were to convert the
data to RGB one would need to examine two pixels from columns N and N+1
(where N is even) to deduce the RGB color.
IP Status
None
Issues
None
New Procedures and Functions
None
New Tokens
Accepted by the <internalFormat> and <format> parameters of
TexImage2D and TexSubImage2D:
YCBCR_MESA 0x8757
Accepted by the <type> parameter of TexImage2D and TexSubImage2D:
UNSIGNED_SHORT_8_8_MESA 0x85BA /* same as Apple's */
UNSIGNED_SHORT_8_8_REV_MESA 0x85BB /* same as Apple's */
Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
None
Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
In section 3.6.4, Rasterization of Pixel Rectangles, on page 101,
add the following to Table 3.8 (Packed pixel formats):
type Parameter GL Data Number of Matching
Token Name Type Components Pixel Formats
-------------- ------- ---------- -------------
UNSIGNED_SHORT_8_8_MESA ushort 2 YCBCR_MESA
UNSIGNED_SHORT_8_8_REV_MESA ushort 2 YCBCR_MESA
In section 3.6.4, Rasterization of Pixel Rectangles, on page 102,
add the following to Table 3.10 (UNSIGNED_SHORT formats):
UNSIGNED_SHORT_8_8_MESA:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
+-------------------------------+-------------------------------+
| 1st | 2nd |
+-------------------------------+-------------------------------+
UNSIGNED_SHORT_8_8_REV_MESA:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
+-------------------------------+-------------------------------+
| 2nd | 1st |
+-------------------------------+-------------------------------+
In section 3.6.4, Rasterization of Pixel Rectangles, on page 104,
add the following to Table 3.12 (Packed pixel fiedl assignments):
First Second Third Fourth
Format Element Element Element Element
------ ------- ------- ------- -------
YCBCR_MESA luminance chroma
In section 3.8.1, Texture Image Specification, on page 125, add
another item to the list of TexImage2D and TexImage3D equivalence
exceptions:
* The value of internalformat and format may be YCBCR_MESA to
indicate that the image data is in YCbCr format. type must
be either UNSIGNED_SHORT_8_8_MESA or UNSIGNED_SHORT_8_8_REV_MESA
as seen in tables 3.8 and 3.10. Table 3.12 describes the mapping
between Y and Cb/Cr to the components.
If NV_texture_rectangle is supported target may also be
TEXTURE_RECTANGLE_NV or PROXY_TEXTURE_RECTANGLE_NV.
All pixel transfer operations are bypassed. The texture is stored as
YCbCr, not RGB. Queries of the texture's red, green and blue component
sizes will return zero. The YCbCr colors are converted to RGB during
texture sampling using an implementation dependent conversion.
In section 3.8.1, Texture Image Specification, on page 126, add
another item to the list of TexImage1D and TexImage2D equivalence
exceptions:
* The value of internalformat and format can not be YCBCR_MESA.
In section 3.8.2, Alternate Texture Image Specification Commands, on
page 129, insert this paragraph after the first full paragraph on the
page:
"If the internal storage format of the image being updated by
TexSubImage2D is YCBCR_MESA then format must be YCBCR_MESA.
The error INVALID_OPERATION will be generated otherwise."
Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
Operations and the Frame Buffer)
None
Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
None
Additions to Chapter 6 of the OpenGL 1.4 Specification (State and
State Requests)
None
Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
None
Additions to the AGL/GLX/WGL Specifications
None
GLX Protocol
None
Errors
INVALID_ENUM is generated by TexImage2D if <internalFormat> is
MESA_YCBCR but <format> is not MESA_YCBCR.
INVALID_ENUM is generated by TexImage2D if <format> is MESA_YCBCR but
<internalFormat> is not MESA_YCBCR.
INVALID_VALUE is generated by TexImage2D if <format> is MESA_YCBCR and
<internalFormat> is MESA_YCBCR and <border> is not zero.
INVALID_OPERATION is generated by TexSubImage2D if the internal image
format is YCBCR_MESA and <format> is not YCBCR_MESA.
INVALID_OPERATION is generated by CopyTexSubImage2D if the internal
image is YCBCR_MESA.
New State
Edit table 6.16 on page 231: change the type of TEXTURE_INTERNAL_FORMAT
from n x Z42 to n x Z43 to indicate that internal format may also be
YCBCR_MESA.
Revision History
20 September 2002 - Initial draft
29 April 2003 - minor updates
3 September 2003 - further clarify when YCbCr->RGB conversion takes place
19 September 2003 - a few more updates prior to submitting to extension
registry.
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