Name

    NV_texture_env_combine4

Name Strings

    GL_NV_texture_env_combine4

Contact

    Michael Gold, NVIDIA Corporation (gold 'at' nvidia.com)

Notice

    Copyright NVIDIA Corporation, 1999, 2000, 2001.

IP Status

    NVIDIA Proprietary.

Version

    NVIDIA date: January 18, 2001
    Version:     14

Number

    195

Dependencies

    EXT_texture_env_combine is required and is modified by this extension
    ARB_multitexture affects the definition of this extension

Overview

    New texture environment function COMBINE4_NV allows programmable
    texture combiner operations, including

        ADD                     Arg0 * Arg1 + Arg2 * Arg3
        ADD_SIGNED_EXT          Arg0 * Arg1 + Arg2 * Arg3 - 0.5

    where Arg0, Arg1, Arg2 and Arg3 are derived from

        ZERO                    the value 0
        PRIMARY_COLOR_EXT       primary color of incoming fragment
        TEXTURE                 texture color of corresponding texture unit
        CONSTANT_EXT            texture environment constant color
        PREVIOUS_EXT            result of previous texture environment; on
                                texture unit 0, this maps to PRIMARY_COLOR_EXT
        TEXTURE<n>_ARB          texture color of the <n>th texture unit

    In addition, the result may be scaled by 1.0, 2.0 or 4.0.

Issues

    None

New Procedures and Functions

    None

New Tokens

    Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv, and
    TexEnviv when the <pname> parameter value is TEXTURE_ENV_MODE

        COMBINE4_NV                                     0x8503

    Accepted by the <pname> parameter of GetTexEnvfv, GetTexEnviv,
    TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the <target> parameter
    value is TEXTURE_ENV

        SOURCE3_RGB_NV                                  0x8583
        SOURCE3_ALPHA_NV                                0x858B
        OPERAND3_RGB_NV                                 0x8593
        OPERAND3_ALPHA_NV                               0x859B

    Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv, and
    TexEnviv when the <pname> parameter value is SOURCE0_RGB_EXT,
    SOURCE1_RGB_EXT, SOURCE2_RGB_EXT, SOURCE3_RGB_NV, SOURCE0_ALPHA_EXT,
    SOURCE1_ALPHA_EXT, SOURCE2_ALPHA_EXT, or SOURCE3_ALPHA_NV

        ZERO
        TEXTURE<n>_ARB

    where <n> is in the range 0 to NUMBER_OF_TEXTURE_UNITS_ARB-1.

    Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv, and
    TexEnviv when the <pname> parameter value is OPERAND0_RGB_EXT,
    OPERAND1_RGB_EXT, OPERAND2_RGB_EXT or OPERAND3_RGB_NV

        SRC_COLOR
        ONE_MINUS_SRC_COLOR
        SRC_ALPHA
        ONE_MINUS_SRC_ALPHA     

    Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv, and
    TexEnviv when the <pname> parameter value is OPERAND0_ALPHA_EXT,
    OPERAND1_ALPHA_EXT, OPERAND2_ALPHA_EXT, or OPERAND3_ALPHA_NV

        SRC_ALPHA
        ONE_MINUS_SRC_ALPHA     

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

    None

Additions to Chapter 3 of the OpenGL 1.2 Specification (Rasterization)

    Added to subsection 3.8.9, before the paragraph describing the state
    requirements:

    If the value of TEXTURE_ENV_MODE is COMBINE4_NV, the form of the
    texture function depends on the values of COMBINE_RGB_EXT and
    COMBINE_ALPHA_EXT, according to table 3.21.  The RGB and ALPHA results
    of the texture function are then multiplied by the values of
    RGB_SCALE_EXT and ALPHA_SCALE, respectively.  The results are clamped
    to [0,1].  If the value of COMBINE_RGB_EXT or COMBINE_ALPHA_EXT is not
    one of the listed values, the result is undefined.

        COMBINE_RGB_EXT or
        COMBINE_ALPHA_EXT       Texture Function
        ------------------      ----------------
        ADD                     Arg0 * Arg1 + Arg2 * Arg3
        ADD_SIGNED_EXT          Arg0 * Arg1 + Arg2 * Arg3 - 0.5

        Table 3.21: COMBINE4_NV texture functions

    The arguments Arg0, Arg1, Arg2 and Arg3 are determined by the values
    of SOURCE<n>_RGB_EXT, SOURCE<n>_ALPHA_EXT, OPERAND<n>_RGB_EXT and
    OPERAND<n>_ALPHA_EXT.  In the following two tables, Ct and At are the
    filtered texture RGB and alpha values; Cc and Ac are the texture
    environment RGB and alpha values; Cf and Af are the RGB and alpha of
    the primary color of the incoming fragment; and Cp and Ap are the RGB
    and alpha values resulting from the previous texture environment.  On
    texture environment 0, Cp and Ap are identical to Cf and Af,
    respectively.  Ct<n> and At<n> are the filtered texture RGB and alpha
    values from the texture bound to the <n>th texture unit.  If the <n>th
    texture unit is disabled, the value of each component is 1.  The
    relationship is described in tables 3.22 and 3.23.

        SOURCE<n>_RGB_EXT       OPERAND<n>_RGB_EXT      Argument
        -----------------       --------------          --------
        ZERO                    SRC_COLOR               0
                                ONE_MINUS_SRC_COLOR     1
                                SRC_ALPHA               0
                                ONE_MINUS_SRC_ALPHA     1
        TEXTURE                 SRC_COLOR               Ct
                                ONE_MINUS_SRC_COLOR     (1-Ct)
                                SRC_ALPHA               At
                                ONE_MINUS_SRC_ALPHA     (1-At)
        CONSTANT_EXT            SRC_COLOR               Cc
                                ONE_MINUS_SRC_COLOR     (1-Cc)
                                SRC_ALPHA               Ac
                                ONE_MINUS_SRC_ALPHA     (1-Ac)
        PRIMARY_COLOR_EXT       SRC_COLOR               Cf
                                ONE_MINUS_SRC_COLOR     (1-Cf)
                                SRC_ALPHA               Af
                                ONE_MINUS_SRC_ALPHA     (1-Af)
        PREVIOUS_EXT            SRC_COLOR               Cp
                                ONE_MINUS_SRC_COLOR     (1-Cp)
                                SRC_ALPHA               Ap
                                ONE_MINUS_SRC_ALPHA     (1-Ap)
        TEXTURE<n>_ARB          SRC_COLOR               Ct<n>
                                ONE_MINUS_SRC_COLOR     (1-Ct<n>)
                                SRC_ALPHA               At<n>
                                ONE_MINUS_SRC_ALPHA     (1-At<n>)

        Table 3.22: Arguments for COMBINE_RGB_EXT functions

        SOURCE<n>_ALPHA_EXT     OPERAND<n>_ALPHA_EXT    Argument
        -----------------       --------------          --------
        ZERO                    SRC_ALPHA               0
                                ONE_MINUS_SRC_ALPHA     1
        TEXTURE                 SRC_ALPHA               At
                                ONE_MINUS_SRC_ALPHA     (1-At)
        CONSTANT_EXT            SRC_ALPHA               Ac
                                ONE_MINUS_SRC_ALPHA     (1-Ac)
        PRIMARY_COLOR_EXT       SRC_ALPHA               Af
                                ONE_MINUS_SRC_ALPHA     (1-Af)
        PREVIOUS_EXT            SRC_ALPHA               Ap
                                ONE_MINUS_SRC_ALPHA     (1-Ap)
        TEXTURE<n>_ARB          SRC_ALPHA               At<n>
                                ONE_MINUS_SRC_ALPHA     (1-At<n>)

        Table 3.23: Arguments for COMBINE_ALPHA_EXT functions

Additions to Chapter 4 of the OpenGL 1.2 Specification (Per-Fragment Operations
and the Framebuffer)

    None

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

    None

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

    None

Additions to the AGL/GLX/WGL Specifications

    None

GLX Protocol

    None

Errors

    INVALID_ENUM is generated if <params> value for SOURCE0_RGB_EXT,
    SOURCE1_RGB_EXT, SOURCE2_RGB_EXT, SOURCE3_RGB_NV, SOURCE0_ALPHA_EXT,
    SOURCE1_ALPHA_EXT, SOURCE2_ALPHA_EXT or SOURCE3_ALPHA_NV is not one of
    ZERO, TEXTURE, CONSTANT_EXT, PRIMARY_COLOR_EXT, PREVIOUS_EXT or
    TEXTURE<n>_ARB, where <n> is in the range 0 to
    NUMBER_OF_TEXTURE_UNITS_ARB-1.

    INVALID_ENUM is generated if <params> value for OPERAND0_RGB_EXT,
    OPERAND1_RGB_EXT, OPERAND2_RGB_EXT or OPERAND3_RGB_NV is not one of
    SRC_COLOR, ONE_MINUS_SRC_COLOR, SRC_ALPHA or ONE_MINUS_SRC_ALPHA.

    INVALID_ENUM is generated if <params> value for OPERAND0_ALPHA_EXT
    OPERAND1_ALPHA_EXT, OPERAND2_ALPHA_EXT, or OPERAND3_ALPHA_NV is not
    one of SRC_ALPHA or ONE_MINUS_SRC_ALPHA.

Modifications to EXT_texture_env_combine

    This extension relaxes the restrictions on SOURCE<n>_RGB_EXT,
    SOURCE<n>_ALPHA_EXT, OPERAND<n>_RGB_EXT and OPERAND<n>_ALPHA_EXT for
    use with EXT_texture_env_combine.  All params specified by Table 3.22
    and Table 3.23 are valid.

Dependencies on ARB_multitexture

    If ARB_multitexture is not implemented, all references to
    TEXTURE<n>_ARB and NUMBER_OF_TEXTURE_UNITS_ARB are deleted.

New State

 Get Value           Get Command    Type      Initial Value        Attribute
 ---------           -----------    ----      -------------        ---------
 SOURCE3_RGB_NV      GetTexEnviv    n x Z5+n  ZERO                 texture
 SOURCE3_ALPHA_NV    GetTexEnviv    n x Z5+n  ZERO                 texture
 OPERAND3_RGB_NV     GetTexEnviv    n x Z2    ONE_MINUS_SRC_COLOR  texture
 OPERAND3_ALPHA_NV   GetTexEnviv    n x Z2    ONE_MINUS_SRC_ALPHA  texture

New Implementation Dependent State

    None

NVIDIA Implementation Details

    Because of a hardware limitation, TNT, TNT2, GeForce, and Quadro
    treat "scale by 4.0" with the COMBINE_RGB_EXT or COMBINE_ALPHA_EXT
    mode of ADD_SIGNED_EXT as "scale by 2.0".

Revision History

    2/22/00 mjk - added NVIDIA Implementation Details