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docs/_extra/specs/MESA_pack_invert.spec

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+Name
+
+    MESA_pack_invert
+
+Name Strings
+
+    GL_MESA_pack_invert
+
+Contact
+
+    Brian Paul, Tungsten Graphics, Inc. (brian.paul 'at' tungstengraphics.com)
+    Keith Whitwell, Tungsten Graphics, Inc.  (keith 'at' tungstengraphics.com)
+
+Status
+
+    Shipping (Mesa 4.0.4 and later)
+
+Version
+
+    1.0
+
+Number
+
+    TBD
+
+Dependencies
+
+    OpenGL 1.0 or later is required
+    This extensions is written against the OpenGL 1.4 Specification.
+
+Overview
+
+    This extension adds a new pixel storage parameter to indicate that
+    images are to be packed in top-to-bottom order instead of OpenGL's
+    conventional bottom-to-top order.  Only pixel packing can be
+    inverted (i.e. for glReadPixels, glGetTexImage, glGetConvolutionFilter,
+    etc).
+
+    Almost all known image file formats store images in top-to-bottom
+    order.  As it is, OpenGL reads images from the frame buffer in
+    bottom-to-top order.  Thus, images usually have to be inverted before
+    writing them to a file with image I/O libraries.  This extension
+    allows images to be read such that inverting isn't needed.
+
+IP Status
+
+    None
+
+Issues
+
+    1. Should we also define UNPACK_INVERT_MESA for glDrawPixels, etc?
+
+    Resolved:  No, we're only concerned with pixel packing.  There are other
+    solutions for inverting images when using glDrawPixels (negative Y pixel
+    zoom) or glTexImage (invert the vertex T coordinates).  It would be easy
+    enough to define a complementary extension for pixel packing in the
+    future if needed.
+
+New Procedures and Functions
+
+    None
+
+New Tokens
+
+    Accepted by the <pname> parameter of PixelStorei and PixelStoref
+    and the <pname> parameter of GetIntegerv, GetFloatv, GetDoublev
+    and GetBooleanv:
+
+        PACK_INVERT_MESA                   0x8758
+
+Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
+
+    None
+
+Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
+
+    None
+
+Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
+Operations and the Frame Buffer)
+
+    Add the following entry to table 4.4 (PixelStore parameters) on page 182:
+
+    Parameter Name       Type    Initial Value    Valid Range
+    ---------------------------------------------------------
+    PACK_INVERT_MESA     boolean     FALSE        TRUE/FALSE
+
+    In the section labeled "Placement in Client Memory" on page 184
+    insert the following text into the paragraph before the sentence
+    that starts with "If the format is RED, GREEN, BLUE...":
+
+    "The parameter PACK_INVERT_MESA controls whether the image is packed
+     in bottom-to-top order (the default) or top-to-bottom order.  Equation
+     3.8 is modified as follows:
+
+     ... the first element of the Nth row is indicated by
+
+         p + Nk,                if PACK_INVERT_MESA is false
+         p + k * (H - 1) - Nk,  if PACK_INVERT_MESA is true, where H is the
+                                image height
+    "
+
+Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
+
+    None
+
+Additions to Chapter 6 of the OpenGL 1.4 Specification (State and
+State Requests)
+
+    None
+
+Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
+
+    None
+
+Additions to the AGL/GLX/WGL Specifications
+
+    None
+
+GLX Protocol
+
+    None
+
+Errors
+
+    None
+
+New State
+
+    Add the following entry to table 6.20 (Pixels) on page 235:
+
+    Get Value         Type     Get Cmd    Initial Value  Description                Sec    Attribute
+    --------------------------------------------------------------------------------------------------
+    PACK_INVERT_MESA  boolean  GetBoolean  FALSE         Value of PACK_INVERT_MESA  4.3.2  pixel-store
+
+Revision History
+
+    21 September 2002 - Initial draft