docs/MESA_ycbcr_texture.spec

   1 Name
   2
   3     MESA_ycbcr_texture
   4
   5 Name Strings
   6
   7     GL_MESA_ycbcr_texture
   8
   9 Contact
  10
  11     Brian Paul, Tungsten Graphics, Inc. (brian.paul 'at' tungstengraphics.com)
  12     Keith Whitwell, Tungsten Graphics, Inc.  (keith 'at' tungstengraphics.com)
  13
  14 Status
  15
  16     Shipping (Mesa 4.0.4 and later)
  17
  18 Version
  19
  20     1.0
  21
  22 Number
  23
  24     TBD
  25
  26 Dependencies
  27
  28     OpenGL 1.0 or later is required
  29     This extensions is written against the OpenGL 1.4 Specification.
  30     NV_texture_rectangle effects the definition of this extension.
  31
  32 Overview
  33
  34     This extension supports texture images stored in the YCbCr format.
  35     There is no support for converting YCbCr images to RGB or vice versa
  36     during pixel transfer.  The texture's YCbCr colors are converted to
  37     RGB during texture sampling, after-which, all the usual per-fragment
  38     operations take place.  Only 2D texture images are supported (not
  39     glDrawPixels, glReadPixels, etc).
  40
  41     A YCbCr pixel (texel) is a 16-bit unsigned short with two components.
  42     The first component is luminance (Y).  For pixels in even-numbered
  43     image columns, the second component is Cb.  For pixels in odd-numbered
  44     image columns, the second component is Cr.  If one were to convert the
  45     data to RGB one would need to examine two pixels from columns N and N+1
  46     (where N is even) to deduce the RGB color.
  47
  48 IP Status
  49
  50     None
  51
  52 Issues
  53
  54     None
  55
  56 New Procedures and Functions
  57
  58     None
  59
  60 New Tokens
  61
  62     Accepted by the <internalFormat> and <format> parameters of
  63     TexImage2D and TexSubImage2D:
  64
  65         YCBCR_MESA                   0x8757
  66
  67     Accepted by the <type> parameter of TexImage2D and TexSubImage2D:
  68
  69         UNSIGNED_SHORT_8_8_MESA      0x85BA /* same as Apple's */
  70         UNSIGNED_SHORT_8_8_REV_MESA  0x85BB /* same as Apple's */
  71
  72 Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
  73
  74     None
  75
  76 Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
  77
  78     In section 3.6.4, Rasterization of Pixel Rectangles, on page 101,
  79     add the following to Table 3.8 (Packed pixel formats):
  80
  81     type Parameter                GL Data   Number of        Matching
  82      Token Name                    Type     Components     Pixel Formats
  83     --------------                -------   ----------     -------------
  84     UNSIGNED_SHORT_8_8_MESA       ushort         2         YCBCR_MESA
  85     UNSIGNED_SHORT_8_8_REV_MESA   ushort         2         YCBCR_MESA
  86
  87
  88     In section 3.6.4, Rasterization of Pixel Rectangles, on page 102,
  89     add the following to Table 3.10 (UNSIGNED_SHORT formats):
  90
  91     UNSIGNED_SHORT_8_8_MESA:
  92
  93       15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
  94     +-------------------------------+-------------------------------+
  95     |              1st              |              2nd              |
  96     +-------------------------------+-------------------------------+
  97
  98     UNSIGNED_SHORT_8_8_REV_MESA:
  99
 100       15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
 101     +-------------------------------+-------------------------------+
 102     |              2nd              |              1st              |
 103     +-------------------------------+-------------------------------+
 104
 105
 106     In section 3.6.4, Rasterization of Pixel Rectangles, on page 104,
 107     add the following to Table 3.12 (Packed pixel fiedl assignments):
 108
 109                        First       Second     Third      Fourth
 110     Format             Element     Element    Element    Element
 111     ------             -------     -------    -------    -------
 112     YCBCR_MESA         luminance   chroma
 113
 114
 115     In section 3.8.1, Texture Image Specification, on page 125, add
 116     another item to the list of TexImage2D and TexImage3D equivalence
 117     exceptions:
 118
 119     * The value of internalformat and format may be YCBCR_MESA to
 120       indicate that the image data is in YCbCr format.  type must
 121       be either UNSIGNED_SHORT_8_8_MESA or UNSIGNED_SHORT_8_8_REV_MESA
 122       as seen in tables 3.8 and 3.10.  Table 3.12 describes the mapping
 123       between Y and Cb/Cr to the components.
 124       If NV_texture_rectangle is supported target may also be
 125       TEXTURE_RECTANGLE_NV or PROXY_TEXTURE_RECTANGLE_NV.
 126       All pixel transfer operations are bypassed.  The texture is stored as
 127       YCbCr, not RGB.  Queries of the texture's red, green and blue component
 128       sizes will return zero.  The YCbCr colors are converted to RGB during
 129       texture sampling using an implementation dependent conversion.
 130
 131
 132     In section 3.8.1, Texture Image Specification, on page 126, add
 133     another item to the list of TexImage1D and TexImage2D equivalence
 134     exceptions:
 135
 136     * The value of internalformat and format can not be YCBCR_MESA.
 137
 138
 139     In section 3.8.2, Alternate Texture Image Specification Commands, on
 140     page 129, insert this paragraph after the first full paragraph on the
 141     page:
 142
 143          "If the internal storage format of the image being updated by
 144     TexSubImage2D is YCBCR_MESA then format must be YCBCR_MESA.
 145     The error INVALID_OPERATION will be generated otherwise."
 146
 147
 148 Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
 149 Operations and the Frame Buffer)
 150
 151     None
 152
 153 Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
 154
 155     None
 156
 157 Additions to Chapter 6 of the OpenGL 1.4 Specification (State and
 158 State Requests)
 159
 160     None
 161
 162 Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
 163
 164     None
 165
 166 Additions to the AGL/GLX/WGL Specifications
 167
 168     None
 169
 170 GLX Protocol
 171
 172     None
 173
 174 Errors
 175
 176     INVALID_ENUM is generated by TexImage2D if <internalFormat> is
 177     MESA_YCBCR but <format> is not MESA_YCBCR.
 178
 179     INVALID_ENUM is generated by TexImage2D if <format> is MESA_YCBCR but
 180     <internalFormat> is not MESA_YCBCR.
 181
 182     INVALID_VALUE is generated by TexImage2D if <format> is MESA_YCBCR and
 183     <internalFormat> is MESA_YCBCR and <border> is not zero.
 184
 185     INVALID_OPERATION is generated by TexSubImage2D if the internal image
 186     format is YCBCR_MESA and <format> is not YCBCR_MESA.
 187
 188     INVALID_OPERATION is generated by CopyTexSubImage2D if the internal
 189     image is YCBCR_MESA.
 190
 191 New State
 192
 193     Edit table 6.16 on page 231: change the type of TEXTURE_INTERNAL_FORMAT
 194     from n x Z42 to n x Z43 to indicate that internal format may also be
 195     YCBCR_MESA.
 196
 197 Revision History
 198
 199     20 September 2002 - Initial draft
 200     29 April 2003 - minor updates
 201      3 September 2003 - further clarify when YCbCr->RGB conversion takes place
 202     19 September 2003 - a few more updates prior to submitting to extension
 203                         registry.
 204      3 April 2004 - fix assorted inaccuracies