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      1 Name
      2 
      3     MESA_pack_invert
      4 
      5 Name Strings
      6 
      7     GL_MESA_pack_invert
      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 
     31 Overview
     32 
     33     This extension adds a new pixel storage parameter to indicate that
     34     images are to be packed in top-to-bottom order instead of OpenGL's
     35     conventional bottom-to-top order.  Only pixel packing can be
     36     inverted (i.e. for glReadPixels, glGetTexImage, glGetConvolutionFilter,
     37     etc).
     38 
     39     Almost all known image file formats store images in top-to-bottom
     40     order.  As it is, OpenGL reads images from the frame buffer in
     41     bottom-to-top order.  Thus, images usually have to be inverted before
     42     writing them to a file with image I/O libraries.  This extension
     43     allows images to be read such that inverting isn't needed.
     44 
     45 IP Status
     46 
     47     None
     48 
     49 Issues
     50 
     51     1. Should we also define UNPACK_INVERT_MESA for glDrawPixels, etc?
     52 
     53     Resolved:  No, we're only concerned with pixel packing.  There are other
     54     solutions for inverting images when using glDrawPixels (negative Y pixel
     55     zoom) or glTexImage (invert the vertex T coordinates).  It would be easy
     56     enough to define a complementary extension for pixel packing in the
     57     future if needed.
     58 
     59 New Procedures and Functions
     60 
     61     None
     62 
     63 New Tokens
     64 
     65     Accepted by the <pname> parameter of PixelStorei and PixelStoref
     66     and the <pname> parameter of GetIntegerv, GetFloatv, GetDoublev
     67     and GetBooleanv:
     68 
     69         PACK_INVERT_MESA                   0x8758
     70 
     71 Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
     72 
     73     None
     74 
     75 Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
     76 
     77     None
     78 
     79 Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
     80 Operations and the Frame Buffer)
     81 
     82     Add the following entry to table 4.4 (PixelStore parameters) on page 182:
     83 
     84     Parameter Name       Type    Initial Value    Valid Range
     85     ---------------------------------------------------------
     86     PACK_INVERT_MESA     boolean     FALSE        TRUE/FALSE
     87 
     88     In the section labeled "Placement in Client Memory" on page 184
     89     insert the following text into the paragraph before the sentence
     90     that starts with "If the format is RED, GREEN, BLUE...":
     91 
     92     "The parameter PACK_INVERT_MESA controls whether the image is packed
     93      in bottom-to-top order (the default) or top-to-bottom order.  Equation
     94      3.8 is modified as follows:
     95 
     96      ... the first element of the Nth row is indicated by
     97 
     98          p + Nk,                if PACK_INVERT_MESA is false
     99          p + k * (H - 1) - Nk,  if PACK_INVERT_MESA is true, where H is the
    100                                 image height
    101     "
    102 
    103 Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
    104 
    105     None
    106 
    107 Additions to Chapter 6 of the OpenGL 1.4 Specification (State and
    108 State Requests)
    109 
    110     None
    111 
    112 Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
    113 
    114     None
    115 
    116 Additions to the AGL/GLX/WGL Specifications
    117 
    118     None
    119 
    120 GLX Protocol
    121 
    122     None
    123 
    124 Errors
    125 
    126     None
    127 
    128 New State
    129 
    130     Add the following entry to table 6.20 (Pixels) on page 235:
    131 
    132     Get Value         Type     Get Cmd    Initial Value  Description                Sec    Attribute
    133     --------------------------------------------------------------------------------------------------
    134     PACK_INVERT_MESA  boolean  GetBoolean  FALSE         Value of PACK_INVERT_MESA  4.3.2  pixel-store
    135 
    136 Revision History
    137 
    138     21 September 2002 - Initial draft
    139