205 lines
6.5 KiB
Python
205 lines
6.5 KiB
Python
Name
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MESA_ycbcr_texture
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Name Strings
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GL_MESA_ycbcr_texture
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Contact
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Brian Paul, Tungsten Graphics, Inc. (brian.paul 'at' tungstengraphics.com)
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Keith Whitwell, Tungsten Graphics, Inc. (keith 'at' tungstengraphics.com)
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Status
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Shipping (Mesa 4.0.4 and later)
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Version
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1.0
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Number
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TBD
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Dependencies
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OpenGL 1.0 or later is required
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This extensions is written against the OpenGL 1.4 Specification.
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NV_texture_rectangle effects the definition of this extension.
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Overview
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This extension supports texture images stored in the YCbCr format.
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There is no support for converting YCbCr images to RGB or vice versa
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during pixel transfer. The texture's YCbCr colors are converted to
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RGB during texture sampling, after-which, all the usual per-fragment
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operations take place. Only 2D texture images are supported (not
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glDrawPixels, glReadPixels, etc).
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A YCbCr pixel (texel) is a 16-bit unsigned short with two components.
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The first component is luminance (Y). For pixels in even-numbered
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image columns, the second component is Cb. For pixels in odd-numbered
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image columns, the second component is Cr. If one were to convert the
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data to RGB one would need to examine two pixels from columns N and N+1
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(where N is even) to deduce the RGB color.
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IP Status
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None
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Issues
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None
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New Procedures and Functions
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None
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New Tokens
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Accepted by the <internalFormat> and <format> parameters of
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TexImage2D and TexSubImage2D:
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YCBCR_MESA 0x8757
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Accepted by the <type> parameter of TexImage2D and TexSubImage2D:
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UNSIGNED_SHORT_8_8_MESA 0x85BA /* same as Apple's */
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UNSIGNED_SHORT_8_8_REV_MESA 0x85BB /* same as Apple's */
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Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
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None
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Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
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In section 3.6.4, Rasterization of Pixel Rectangles, on page 101,
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add the following to Table 3.8 (Packed pixel formats):
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type Parameter GL Data Number of Matching
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Token Name Type Components Pixel Formats
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-------------- ------- ---------- -------------
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UNSIGNED_SHORT_8_8_MESA ushort 2 YCBCR_MESA
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UNSIGNED_SHORT_8_8_REV_MESA ushort 2 YCBCR_MESA
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In section 3.6.4, Rasterization of Pixel Rectangles, on page 102,
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add the following to Table 3.10 (UNSIGNED_SHORT formats):
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UNSIGNED_SHORT_8_8_MESA:
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15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
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+-------------------------------+-------------------------------+
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| 1st | 2nd |
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+-------------------------------+-------------------------------+
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UNSIGNED_SHORT_8_8_REV_MESA:
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15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
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+-------------------------------+-------------------------------+
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| 2nd | 1st |
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+-------------------------------+-------------------------------+
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In section 3.6.4, Rasterization of Pixel Rectangles, on page 104,
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add the following to Table 3.12 (Packed pixel fiedl assignments):
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First Second Third Fourth
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Format Element Element Element Element
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------ ------- ------- ------- -------
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YCBCR_MESA luminance chroma
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In section 3.8.1, Texture Image Specification, on page 125, add
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another item to the list of TexImage2D and TexImage3D equivalence
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exceptions:
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* The value of internalformat and format may be YCBCR_MESA to
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indicate that the image data is in YCbCr format. type must
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be either UNSIGNED_SHORT_8_8_MESA or UNSIGNED_SHORT_8_8_REV_MESA
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as seen in tables 3.8 and 3.10. Table 3.12 describes the mapping
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between Y and Cb/Cr to the components.
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If NV_texture_rectangle is supported target may also be
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TEXTURE_RECTANGLE_NV or PROXY_TEXTURE_RECTANGLE_NV.
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All pixel transfer operations are bypassed. The texture is stored as
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YCbCr, not RGB. Queries of the texture's red, green and blue component
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sizes will return zero. The YCbCr colors are converted to RGB during
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texture sampling using an implementation dependent conversion.
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In section 3.8.1, Texture Image Specification, on page 126, add
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another item to the list of TexImage1D and TexImage2D equivalence
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exceptions:
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* The value of internalformat and format can not be YCBCR_MESA.
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In section 3.8.2, Alternate Texture Image Specification Commands, on
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page 129, insert this paragraph after the first full paragraph on the
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page:
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"If the internal storage format of the image being updated by
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TexSubImage2D is YCBCR_MESA then format must be YCBCR_MESA.
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The error INVALID_OPERATION will be generated otherwise."
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Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
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Operations and the Frame Buffer)
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None
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Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
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None
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Additions to Chapter 6 of the OpenGL 1.4 Specification (State and
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State Requests)
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None
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Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
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None
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Additions to the AGL/GLX/WGL Specifications
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None
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GLX Protocol
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None
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Errors
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INVALID_ENUM is generated by TexImage2D if <internalFormat> is
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MESA_YCBCR but <format> is not MESA_YCBCR.
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INVALID_ENUM is generated by TexImage2D if <format> is MESA_YCBCR but
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<internalFormat> is not MESA_YCBCR.
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INVALID_VALUE is generated by TexImage2D if <format> is MESA_YCBCR and
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<internalFormat> is MESA_YCBCR and <border> is not zero.
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INVALID_OPERATION is generated by TexSubImage2D if the internal image
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format is YCBCR_MESA and <format> is not YCBCR_MESA.
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INVALID_OPERATION is generated by CopyTexSubImage2D if the internal
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image is YCBCR_MESA.
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New State
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Edit table 6.16 on page 231: change the type of TEXTURE_INTERNAL_FORMAT
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from n x Z42 to n x Z43 to indicate that internal format may also be
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YCBCR_MESA.
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Revision History
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20 September 2002 - Initial draft
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29 April 2003 - minor updates
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3 September 2003 - further clarify when YCbCr->RGB conversion takes place
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19 September 2003 - a few more updates prior to submitting to extension
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registry.
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3 April 2004 - fix assorted inaccuracies
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