GL_SGIX_pixel_texture

Name

    SGIX_pixel_texture

Name Strings

    GL_SGIX_pixel_texture

Version

    Last Modified Date: December 10, 1999
    Author Revision: $Header: //depot/main/doc/registry/extensions/SGI/sgix_pixel_texture.spec#2 $

Number

    15a
    (SGIS_pixel_texture is extension #15)

Dependencies

    None

Overview

    This extension allows the color components of pixel groups to be used as
    texture coordinates, effectively converting a color image into a texture
    coordinate image.  Because texture mapping is essentially a
    multidimensional table lookup, this conversion supports multidimensional
    color lookups for images.  Such multidimensional lookups can be used to
    implement very accurate color space conversions.

Issues

    *	Should LOD be supported?

New Procedures and Functions

    void PixelTexGenSGIX(enum mode);

New Tokens

    Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, and
    by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and
    GetDoublev:

        PIXEL_TEX_GEN_SGIX                      = 0x8139

    Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv,
    and GetDoublev:

        PIXEL_TEX_GEN_MODE_SGIX                 = 0x832B
	

Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)

    None

Additions to Chapter 3 of the 1.0 Specification (Rasterization)

    This extension modifies the "Conversion to Fragments" subsection of
    section 3.6.3 (Rasterization of Pixel Rectangles) of the GL
    Specification.  The paragraph beginning with "A fragment arising from a
    group consisting of color data ..." is replaced by the following:

    A fragment arising from a group consisting of color index data takes on
    the color index of the group; the depth and texture coordinates are
    taken from the current raster positions associated data.  Likewise, a
    fragment arising from a depth component takes the component's depth
    value; the color and texture coordinates are given by those associated
    with the current raster position.  Groups arising from DrawPixels with a
    <format> of STENCIL_INDEX are treated specially and are described in
    section 4.3.1.

    The treatment of fragments arising from groups consisting of RGBA color
    data is affected by pixel texgen, which is enabled and disabled by
    calling Enable and Disable with PIXEL_TEX_GEN_SGIX passed as the <cap>
    parameter.

    When pixel texgen enabled, a fragment arising from a group consisting of
    RGBA color data takes its depth component from the current raster position
    depth, and the texture coordinates are assigned as follows:

      Pixel group's red becomes the fragment S texture coordinate
      Pixel group's green becomes the fragment T texture coordinate
      Pixel group's blue becomes the fragment R texture coordinate
      Pixel group's alpha becomes the fragment Q texture coordinate

    The assignment of the fragment color components is determined by value of
    PIXEL_TEX_GEN_MODE_SGIX as defined as defined by the following table:

      PIXEL_TEX_GEN_MODE_SGIX    Fragment's color component value 
      value		            R          G         B          A
      -----------------------    -------    -------   -------    -------
      NONE         	         PG's R     PG's G    PG's B     PG's A
      ALPHA      	         PG's R     PG's G    PG's B     CRP's A
      RGB			 CRP's R    CRP's G   CRP's B    PG's A
      RGBA       	         CRP's R    CRP's G   CRP's B    CRP's A

      Assignment of pixel group and current raster position color data to a
      fragment arising from an RGBA color pixel group when pixel texgen is
      enabled.  The value of PIXEL_TEX_GEN_MODE_SGIX in the first column
      controls the assignment of fragment color components in second thru the
      fifth columns.  PG, CRP, R, G, B, A are abbreviations of "current raster
      position", "pixel group", "red", "green", "blue", and "alpha"
      respectively.  

    The <mode> parameter of PixelTexGenSGIX is used to set the value of
    PIXEL_TEX_GEN_MODE_SGIX.  (It is NONE by default.)

Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the Frame Buffer)

    The operation of pixel texgen during pixel copy operations is
    identical to the operation during pixel drawing.  Because PixelTexGenSGIX
    defines the rasterization of pixel groups, it has no effect on texture
    definitions or on pixel query (ReadPixels) operations.

Additions to Chapter 5 of the 1.0 Specification (Special Functions)

    None

Additions to Chapter 6 of the 1.0 Specification (State and State Requests)

    None

Additions to the GLX Specification

    None

Errors

    INVALID_ENUM is generated if PixelTexGenSGIX parameter <mode> is not NONE,
    ALPHA, RGB, or RGBA. 

    INVALID_OPERATION is generated if PixelTexGenSGIX is called between
    execution of Begin and the execution of the corresponding End.

New State

    Get Value			Get Command	Type	Initial Value	Attrib
    ---------			-----------	----	-------------	------
    PIXEL_TEX_GEN_SGIX		IsEnabled	B	FALSE		pixel
    PIXEL_TEX_GEN_MODE_SGIX	GetIntegerv	Z4	NONE		pixel

New Implementation Dependent State

    None

Implementation Support

   List of OpenGL implementations supporting the GL_SGIX_pixel_texture extension

Original File

   Original text file for the GL_SGIX_pixel_texture extension