docs/MESA_pack_invert.spec

   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 defined 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