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4358 Serge 1 
Name
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    MESA_pack_invert
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Name Strings
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    GL_MESA_pack_invert
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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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Overview
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    This extension adds a new pixel storage parameter to indicate that
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    images are to be packed in top-to-bottom order instead of OpenGL's
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    conventional bottom-to-top order.  Only pixel packing can be
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    inverted (i.e. for glReadPixels, glGetTexImage, glGetConvolutionFilter,
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    etc).
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    Almost all known image file formats store images in top-to-bottom
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    order.  As it is, OpenGL reads images from the frame buffer in
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    bottom-to-top order.  Thus, images usually have to be inverted before
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    writing them to a file with image I/O libraries.  This extension
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    allows images to be read such that inverting isn't needed.
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IP Status
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    None
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Issues
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    1. Should we also define UNPACK_INVERT_MESA for glDrawPixels, etc?
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    Resolved:  No, we're only concerned with pixel packing.  There are other
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    solutions for inverting images when using glDrawPixels (negative Y pixel
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    zoom) or glTexImage (invert the vertex T coordinates).  It would be easy
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    enough to define a complementary extension for pixel packing in the
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    future if needed.
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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  parameter of PixelStorei and PixelStoref
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    and the  parameter of GetIntegerv, GetFloatv, GetDoublev
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    and GetBooleanv:
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        PACK_INVERT_MESA                   0x8758
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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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    None
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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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    Add the following entry to table 4.4 (PixelStore parameters) on page 182:
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    Parameter Name       Type    Initial Value    Valid Range
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    ---------------------------------------------------------
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    PACK_INVERT_MESA     boolean     FALSE        TRUE/FALSE
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    In the section labeled "Placement in Client Memory" on page 184
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    insert the following text into the paragraph before the sentence
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    that starts with "If the format is RED, GREEN, BLUE...":
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    "The parameter PACK_INVERT_MESA controls whether the image is packed
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     in bottom-to-top order (the default) or top-to-bottom order.  Equation
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     3.8 is modified as follows:
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     ... the first element of the Nth row is indicated by
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         p + Nk,                if PACK_INVERT_MESA is false
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         p + k * (H - 1) - Nk,  if PACK_INVERT_MESA is true, where H is the
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                                image height
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    "
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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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    None
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New State
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    Add the following entry to table 6.20 (Pixels) on page 235:
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    Get Value         Type     Get Cmd    Initial Value  Description                Sec    Attribute
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    --------------------------------------------------------------------------------------------------
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    PACK_INVERT_MESA  boolean  GetBoolean  FALSE         Value of PACK_INVERT_MESA  4.3.2  pixel-store
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Revision History
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    21 September 2002 - Initial draft