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     Copyright NVIDIA Corporation, 2000, 2001, 2004.  
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    NVIDIA Proprietary.  
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homeprevnext Version
    NVIDIA Date: February 11, 2004  
    Version 1.2  
    $Date$ $Revision$  
    $Id: //sw/main/docs/OpenGL/specs/GL_NV_register_combiners2.txt#5 $  
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homeprevnext Dependencies
    Written based on the wording of the OpenGL 1.2.1 specification.  
    Assumes support for the NV_register_combiners extension (version 1.4).  
homeprevnext Overview
    The NV_register_combiners extension provides a powerful fragment  
    coloring mechanism.  This specification extends the register combiners  
    functionality to support more color constant values that are unique  
    for each general combiner stage.  
    The base register combiners functionality supports only two color  
    constants.  These two constants are available in every general  
    combiner stage and in the final combiner.  
    When many general combiner stages are supported, more than two  
    unique color constants is often required.  The obvious way to extend  
    the register combiners is to add several more color constant  
    registers.  But adding new unique color constant registers is  
    expensive for hardware implementation because every color constant  
    register must be available as an input to any stage.  
    In practice however, it is the total set of general combiner stages  
    that requires more color constants, not each and every individual  
    general combiner stage.  Each individual general combiner stage  
    typically requires only one or two color constants.  
    By keeping two color constant registers but making these two registers  
    contain two unique color constant values for each general combiner  
    stage, the hardware expense of supporting multiple color constants  
    is minimized.  Additionally, this scheme scales appropriately as  
    more general combiner stages are added.  
homeprevnext Issues
    How do is compatibility maintained with the original register  
      RESOLUTION:  Initially, per general combiner stage constants are  
      disabled and the register combiners operate as described in the  
      original NV_register_combiners specification.  A distinct "per  
      stage constants" enable exposes this extension's new functionality.  
    Where do the final combiner color constant values come from?  
      RESOLUTION:  When "per stage constants" is enabled, the final  
      combiner color constants continue to use the constant colors set  
      with glCombinerParameterfvNV.  
    Is the alpha component of the SECONDARY_COLOR_NV register now  
    initialized with the expected interpolated secondary color's alpha  
       RESOLUTION:  Yes, see Revision History for details.  
homeprevnext New Procedures and Functions
    void CombinerStageParameterfvNV(GLenum stage,  
                                    GLenum pname,  
                                    const GLfloat *params);  
    void GetCombinerStageParameterfvNV(GLenum stage,  
                                       GLenum pname,  
                                       GLfloat *params);  
homeprevnext New Tokens
    Accepted by the <cap> parameter of Disable, Enable, and IsEnabled,  
    and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv,  
    and GetDoublev:  
        PER_STAGE_CONSTANTS_NV                         0x8535  
    Accepted by the <pname> parameter of CombinerStageParameterfvNV  
    and GetCombinerStageParameterfvNV:  
        CONSTANT_COLOR0_NV                             (see NV_register_combiners)  
        CONSTANT_COLOR1_NV                             (see NV_register_combiners)  
    Accepted by the <stage> parameter of CombinerStageParameterfvNV and  
        COMBINER0_NV                                   (see NV_register_combiners)  
        COMBINER1_NV                                   (see NV_register_combiners)  
        COMBINER2_NV                                   (see NV_register_combiners)  
        COMBINER3_NV                                   (see NV_register_combiners)  
        COMBINER4_NV                                   (see NV_register_combiners)  
        COMBINER5_NV                                   (see NV_register_combiners)  
        COMBINER6_NV                                   (see NV_register_combiners)  
        COMBINER7_NV                                   (see NV_register_combiners)  
homeprevnext Additions to Chapter 2 of the 1.2 Specification (OpenGL Operation)
homeprevnext Additions to Chapter 3 of the 1.2 Specification (Rasterization)
 --  Section 3.8.12 "Register Combiners Application"  
    Because the alpha component of the SECONDARY_COLOR_NV register is  
    well-defined now (see Revision History) to be the alpha value of csec,  
    STRIKE this sentence:  
    "The initial value of the alpha portion of register SECONDARY_COLOR_NV  
    is undefined."  
    Add a paragraph immediately before section  
    "The ccc0 and ccc1 values map to particular constant color values.  
    The ccc0 and ccc1 mappings depend on whether per-stage constants  
    are enabled or not.  Per-stage constants are enabled and disabled  
    with the Enable and Disable commands using the symbolic constant  
    When per-stage constants are disabled, ccc0 and ccc1 are mapped to  
    the register combiners' global color constant values, gccc0 and  
    When per-stage constants are enabled, ccc0 and ccc1 depend  
    on the combiner stage that inputs the COLOR_CONSTANT0_NV and  
    COLOR_CONSTANT1_NV registers.  Each general combiner stage # maps  
    ccc0 and ccc1 to the per-stage values s#ccc0 and s#ccc1 respectively.  
    The final combiner maps ccc0 and ccc1 to the values gccc0 and gccc1  
    (the same as if per-stage constants are disabled).  
    gccc0, gccc1, s#ccc0, and s#ccc1 are further described in the  
    following section."  
 --  Section "Combiner Parameters"  
    Change Table NV_register_combiners.3 to read "gccc0" instead of  
    "ccc0" and "gccc1" instead of "ccc1".  
    Change the first sentence of the last paragraph to read:  
    "The values gccc0 and gccc1 named by CONSTANT_COLOR0_NV and  
    CONSTANT_COLOR1_NV are global constant colors available for inputs to  
    the final combiner stage and, when per-stage constants is disabled,  
    to the general combiner stages."  
    Add the following after the last paragraph in the section:  
    "Per-stage combiner parameters are specified by  
        void CombinerStageParameterfvNV(GLenum stage,  
                                        GLenum pname,  
                                        const GLfloat *params);  
    The <stage> parameter is a symbolic constant of the form  
    COMBINER<#>_NV, indicating the general combiner stage <#> whose  
    parameter named by <pname> is to be updated.  <pname> must be either  
    CONSTANT_COLOR0_NV or CONSTANT_COLOR1_NV.  <params> is a pointer  
    to a group of four values to which to set the indicated parameter.  
    The parameter names CONSTANT_COLOR0_NV and CONSTANT_COLOR1_NV  
    update the per-stage color constants s#ccc0 and s#ccc1 respectively  
    where # is the number of the specified general combiner stage.  
    The floating-point color values are clamped to the range [0,1]  
    when specified."  
homeprevnext Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations and the Frame Buffer)
homeprevnext Additions to Chapter 5 of the 1.2 Specification (Special Functions)
homeprevnext Additions to Chapter 6 of the 1.2 Specification (State and State Requests)
 --  Section 6.1.3 "Enumerated Queries"  
    Add to the bottom of the list of function prototypes (page 183):  
        void GetCombinerStageParameterfvNV(GLenum stage,  
                                           GLenum pname,  
                                           GLfloat *params);  
    Change the first sentence describing the register combiner queries  
    to mention GetCombinerStageParameterfvNV so the sentence reads:  
    "The GetCombinerInputParameterfvNV, GetCombinerInputParameterivNV,  
    GetCombinerOutputParameterfvNV, GetCombinerOutputParameterivNV,  
    and GetCombinerStageParameterfvNV parameter <stage> may be one of  
    COMBINER0_NV, COMBINER1_NV, and so on, indicating which general  
    combiner stage to query."  
homeprevnext Additions to the GLX Specification
homeprevnext GLX Protocol
    Two new GL commands are added.  
    The following rendering command is sent to the sever as part of a  
    glXRender request:  
            2           8+4*n           rendering command length  
            2           ????            rendering command opcode  
            4           ENUM            pname  
                        0x852A   n=4    GL_CONSANT_COLOR0_NV  
                        0x852B   n=4    GL_CONSANT_COLOR1_NV  
                        else     n=0  
            4*n         LISTofFLOAT32   params  
    The remaining command is a non-rendering command.  This commands  
    is sent separately (i.e., not as part of a glXRender or glXRenderLarge  
    request), using the glXVendorPrivateWithReply request:  
            1           CARD8           opcode (X assigned)  
            1           17              GLX opcode (glXVendorPrivateWithReply)  
            2           5               request length  
            4           ????            vendor specific opcode  
            4           GLX_CONTEXT_TAG context tag  
            4           ENUM            stage  
            4           ENUM            pname  
            1           1               reply  
            1                           unused  
            2           CARD16          sequence number  
            4           m               reply length, m = (n==1 ? 0 : n)  
            4                           unused  
            4           CARD32          unused  
            if (n=1) this follows:  
            4           FLOAT32         params  
            12                          unused  
            otherwise this follows:  
            16                          unused  
            n*4         LISTofFLOAT32   params  
homeprevnext Errors
homeprevnext New State
Get Value               Type  Get Command                    Initial Value  Description         Sec       Attribute  
----------------------  ----  -----------------------------  -------------  ------------------  --------  --------------  
PER_STAGE_CONSTANTS_NV  B     IsEnabled                      False          enable for          3.8.12    texture/enable  
CONSTANT_COLOR0_NV      Cx#   GetCombinerStageParameterfvNV  0,0,0,0        per-stage constant  texture  
                                                                            color zero  
CONSTANT_COLOR1_NV      Cx#   GetCombinerStageParameterfvNV  0,0,0,0        per-stage constant  texture  
                                                                             color one  
[ where # is the value of MAX_GENERAL_COMBINERS_NV ]  
New Implementation State  
homeprevnext Revision History
     Version 1.2 (February 11, 2004) - When describing the  
     per-fragment register initialization within the combiners, the  
     NV_register_combiners specification says "The initial value of the  
     alpha portion of register SECONDARY_COLOR_NV is undefined." While  
     this is true of NV1x GPUs, NV2x and beyond GPUs can properly  
     initialize the alpha component of the SECONDARY_COLOR_NV  
     register with the expected interpolated secondary color alpha.  
     Unfortunately, due to a driver bug, the alpha components was always  
     initialized to 1.0 in driver versions 56.90 (circa February 2004)  
     and before.  Drivers subsequent to 56.90 have this problem fixed.  
     This specification is updated to indicate that SECONDARY_COLOR_NV  
     initialization is well-defined and what you would expect now.  
     Version 1.1 (April 28, 2003) - The original specification failed  
     to specify what should happen if a color component parameter for  
     CombinerStageParameter*NV is outside the [0,1] range.  Such values  
     should be clamped to the [0,1] range.  
     NVIDIA drivers prior to May 2003 incorrectly failed to clamp color  
     component values specified with CombinerStageParameter*NV to [0,1].  
     Instead, approximately "x-floor(x)" where x is a component value  
     is used for rendering.  
     is used for rendering.  
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