extensions/SGIX/SGIX_fog_texture.txt

Name

    SGIX_fog_texture

Name Strings

    GL_SGIX_fog_texture

Version

    $Date: 1999/03/30 23:13:53 $ $Revision: 1.5 $

Number

    XXX

Dependencies

    OpenGL 1.1 is required.
    EXT_light_texture is required.
    SGIS_multitexture affects the definition of this extension.
    SGIX_color_range affects the definition of this extension.

Overview

    This extension defines a general mechanism for substituting the
    fragment color computed during texture environment processing in
    place of fog fragment attributes such as fog color, fog density
    fog patchy factor. The application of texture to fog color assumes
    no internal format constraint of the image. Fog density and patchy
    multiplicative factor are scalar values and are substituted
    by the red texture component.

IP Status

    Silicon Graphics has filed for patent protection for some of the
    techniques described in this extension document.

Issues:

    * This extension is incomplete with respect to the dependency
    of the fog_patchy extension

    * The fog patchy factor is expected to be a constant of 1.
    unless is applied by a texture. Is that the most intuitive
    api. Should we support a any constant for the factor and have
    it be set as a fog parameter (in glFog).

New Procedures and Functions

    void TextureFogSGIX(enum pname);

New Tokens

    Accepted by the <mode> parameter of ApplyTextureEXT:

    FRAGMENT_FOG_SGIX                           0xXXXX

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

    TEXTURE_FOG_SGIX                            0xXXXX

    Accepted by the <pname> parameter of TextureFogSGIX:

    FOG_PATCHY_FACTOR_SGIX                      0xXXXX

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

    None

Additions to Chapter 3 of the 1.1 Specification (Rasterization)

    Add at the end of Section 3.X.1 Texture Application

    If <mode> is FRAGMENT_FOG_SGIX then the post-texture-environment
    color substitutes one of fragment fog parameters during the fog
    computation of the fragment. The fragment fog parameters
    substituted are specified by the command TextureFogSGIX
    described in section 3.X.5.

    Add section 3.X.4 and replace 3.X.4 with 3.X.5 for
    Interactions with multiple textures

    3.X.4 Texture Applied to Fog Parameters

    TextureFogSGIX(enum pname) determines which fog fragment parameters
    is substituted with the post-texture-environment color, when the
    texture application mode is FRAGMENT_FOG_SGIX. <pname>  is one of
    FOG_COLOR, FOG_DENSITY or FOG_PATCHY_FACTOR_SGIX. FOG_COLOR can be
    applied with a texture image of any number of components. FOG_DENSITY
    and FOG_PATCHY_FACTOR_SGIX are scalar entities derived from the
    texture red component.

Additions to Chapter 4 of the 1.1 Specification (Per-Fragment Operations
and the Framebuffer)

Additions to Chapter 5 of the 1.1 Specification (Special Functions)

Additions to Chapter 6 of the 1.1 Specification (State and State Requests)

Additions to the GLX Specification

    None

GLX Protocol

    TBD

Dependencies on SGIX_light_texture
    EXT_light_texture is required since this extension adds
    an enumerant parameter to the ApplyTextureEXT command.

Dependencies on EXT_multitexture
    If EXT_multitexture is not supported only the single
    post-texture-environment color is available for substitution and the
    discussion of multiple textures in section 3.X.5 is void.

Errors
    INVALID_ENUM is generated if TextureFogSGIX parameter
    is not FOG_COLOR, FOG_DENSITY, or FOG_PATCHY_FACTOR_SGIX.

New State

    Get Value        Get Command     Type    Initial Value    Attribute
    ---------        -----------     ----    -------------    ---------

    TEXTURE_FOG_SGIX GetIntegerv     Z10     FOG_COLOR        texture

New Implementation Dependent State

    None