GL_NV_texgen_reflection

Name

    NV_texgen_reflection

Name Strings

    GL_NV_texgen_reflection

Contact

    Mark J. Kilgard, NVIDIA Corporation (mjk 'at' nvidia.com)

Notice

    Copyright NVIDIA Corporation, 1999.

Status

    Shipping (version 1.0)
    NVIDIA, Mesa 3.1, and ATI support this.

    This extension's texture coordinate generation functionality is
    incoporated into the ARB_texture_cube_map extension.  The same
    enumerant values are used.

    The ARB_texture_cube_map functionality, including this texgen
    reflection functionality, is part of OpenGL 1.3 and subsequent
    revisions of the core OpenGL standard.

Version

    June 17, 2003
    $Date: 2003/06/17 $ $Revision: #10 $

Number

    179

Dependencies

    Written based on the wording of the OpenGL 1.2 specification but
    not dependent on it.

Overview

    This extension provides two new texture coordinate generation modes
    that are useful texture-based lighting and environment mapping.
    The reflection map mode generates texture coordinates (s,t,r)
    matching the vertex's eye-space reflection vector.  The reflection
    map mode is useful for environment mapping without the singularity
    inherent in sphere mapping.  The normal map mode generates texture
    coordinates (s,t,r) matching the vertex's transformed eye-space
    normal.  The normal map mode is useful for sophisticated cube map
    texturing-based diffuse lighting models.

Issues

    Should we place the normal/reflection vector in the (s,t,r) texture
    coordinates or (s,t,q) coordinates?

      RESOLUTION:  (s,t,r).  Even if the proposed hardware uses "q" for
      the third component, the API should claim to support generation of
      (s,t,r) and let the texture matrix (through a concatenation with
      the user-supplied texture matrix) move "r" into "q".

    Should you be able to have some texture coordinates computing
    REFLECTION_MAP_NV and others not?  Same question with NORMAL_MAP_NV.

      RESOLUTION:  YES. This is the way that SPHERE_MAP works.  It is
      not clear that this would ever be useful though.

    Should something special be said about the handling of the q
    texture coordinate for this spec?

      RESOLUTION:  NO.  But the following paragraph is useful for
      implementors concerned about the handling of q.

      The REFLECTION_MAP_NV and NORMAL_MAP_NV modes are intended to supply
      reflection and normal vectors for cube map texturing hardware.
      When these modes are used for cube map texturing, the generated
      texture coordinates can be thought of as a reflection vector.
      The value of the q texture coordinate then simply scales the
      vector but does not change its direction.  Because only the vector
      direction (not the vector magnitude) matters for cube map texturing,
      implementations are free to leave q undefined when any of the s,
      t, or r texture coordinates are generated using REFLECTION_MAP_NV
      or NORMAL_MAP_NV.

New Procedures and Functions

    None

New Tokens

    Accepted by the <param> parameters of TexGend, TexGenf, and TexGeni
    when <pname> parameter is TEXTURE_GEN_MODE:

        NORMAL_MAP_NV                      0x8511
        REFLECTION_MAP_NV                  0x8512

    When the <pname> parameter of TexGendv, TexGenfv, and TexGeniv is
    TEXTURE_GEN_MODE, then the array <params> may also contain
    NORMAL_MAP_NV or REFLECTION_MAP_NV.

Additions to Chapter 2 of the 1.2 Specification (OpenGL Operation)

 --  Section 2.10.4 "Generating Texture Coordinates"

      Change the last sentence in the 1st paragraph to:

      "If <pname> is TEXTURE_GEN_MODE, then either <params> points to
      or <param> is an integer that is one of the symbolic constants
      OBJECT_LINEAR, EYE_LINEAR, SPHERE_MAP, REFLECTION_MAP_NV, or
      NORMAL_MAP_NV."

      Add these paragraphs after the 4th paragraph:

      "If TEXTURE_GEN_MODE indicates REFLECTION_MAP_NV, compute the
      reflection vector r as described for the SPHERE_MAP mode.  Then the
      value assigned to an s coordinate (the first TexGen argument value
      is S) is s = rx; the value assigned to a t coordinate is t = ry;
      and the value assigned to a r coordinate is r = rz.  Calling TexGen
      with a <coord> of Q when <pname> indicates REFLECTION_MAP_NV
      generates the error INVALID_ENUM.

      If TEXTURE_GEN_MODE indicates NORMAL_MAP_NV, compute the normal
      vector n' as described in section 2.10.3.  Then the value assigned
      to an s coordinate (the first TexGen argument value is S) is s =
      nfx; the value assigned to a t coordinate is t = nfy; and the
      value assigned to a r coordinate is r = nfz.  (The values nfx, nfy,
      and nfz are the components of nf.)  Calling TexGen with a <coord>
      of Q when <pname> indicates REFLECTION_MAP_NV generates the error
      INVALID_ENUM.

      The last paragraph's first sentence should be changed to:

      "The state required for texture coordinate generation comprises a
      five-valued integer for each coordinate indicating coordinate
      generation mode, ..."

Additions to Chapter 3 of the 1.2 Specification (Rasterization)

     None

Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations and the Frame Buffer)

     None

Additions to Chapter 5 of the 1.2 Specification (Special Functions)

     None

Additions to Chapter 6 of the 1.2 Specification (State and State Requests)

     None

Additions to the GLX Specification

     None

Errors

     INVALID_ENUM is generated when TexGen is called with a <coord> of Q
     when <pname> indicates REFLECTION_MAP_NV or NORMAL_MAP_NV.

New State

(table 6.14, p204) change the entry for TEXTURE_GEN_MODE to:

    Get Value            Type    Get Command     Initial Value   Description        Sec    Attribute
    ---------            ----    -----------     -------------   -----------        ------ ---------
    TEXTURE_GEN_MODE     4xZ5    GetTexGeniv    EYE_LINEAR      Function used for  2.10.4 texture
                                                                 texgen (for s,t,r,
                                                                 and q)

(the type changes from 4xZ3 to 4xZ5)

New Implementation State

    None

Revision History

    None

Implementation Support

   List of OpenGL implementations supporting the GL_NV_texgen_reflection extension

Original File

   Original text file for the GL_NV_texgen_reflection extension