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homeprevnext Name
homeprevnext Name Strings
homeprevnext Contact
    Pat Brown, NVIDIA Corporation (pbrown 'at'  
homeprevnext Notice
    Copyright NVIDIA Corporation, 2002.  
homeprevnext IP Status
    NVIDIA Proprietary.  
homeprevnext Status
    Implemented, November 2002  
    Shipping in Release 40 NVIDIA driver for CineFX hardware, January 2003.  
homeprevnext Version
    Last Modified:      $Date: 2005/06/16 $  
    NVIDIA Revision:    4  
homeprevnext Number
homeprevnext Support
    NVIDIA plans to discontinue this extension for future GPU  
    architectures.  Support for NV3x (GeForce FX), NV4x (GeForce 6  
    Series), and G7x (GeForce 7x00) architectures will continue.  
    As an alternative to the EXT_texture_expand_normal functionality,  
    developers can either use the signed fixed-point texture formats  
    provided by NV_texture_shader (such as GL_SIGNED_RGBA8_NV) or perform  
    the "expand normal" operation with shader instructions (typically  
    just a MAD)..  
homeprevnext Dependencies
    OpenGL 1.1 is required.  
homeprevnext Overview
    This extension provides a remapping mode where unsigned texture  
    components (in the range [0,1]) can be treated as though they  
    contained signed data (in the range [-1,+1]).  This allows  
    applications to easily encode signed data into unsigned texture  
    The functionality of this extension is nearly identical to the  
    EXPAND_NORMAL_NV remapping mode provided in the NV_register_combiners  
    extension, although it applies even if register combiners are used.  
homeprevnext Issues
    (1) When is the remapping applied?  
      RESOLVED:  It would be possible to remap after loading each texel,  
      remap after all filtering is done, or something in between.  
      Ignoring implementation-dependent rounding errors, it really  
      doesn't matter.  
      The spec language says that the remapping is applied after filtering  
      texel values within each level.  For LINEAR_MIPMAP_LINEAR, this  
      means that the remapping is "done" twice.  This approach was chosen  
      solely to simplify the spec language, and does not necessarily  
      reflect NVIDIA's implementation.  
    (2) Should the remapping mode apply to textures with signed  
      RESOLVED:  No -- the EXPAND_NORMAL_NV mapping is ignored for  
      such textures.  
    (3) NV_texture_shader provides several internal formats with a mix  
    of signed and unsigned components.  For example, the base formats  
    DSDT_MAG_NV, and DSDT_MAG_INTENSITY_NV have this property, and  
    there is a variant of RGBA where the RGB components are signed,  
    but the A component is unsigned.  What should happen in this case?  
      RESOLVED:  The unsigned components are remapped; the signed  
      components are unmodified.  
    (4) What should be said about signed fixed-point precision and range  
    of actual implementations?  
      RESOLVED:  The fundamental problem is that it is not possible  
      to derive a linear mapping taking unsigned values that exactly  
      represents -1.0, 0.0, and +1.0.  
      The mapping chosen for current NVIDIA implementations does not  
      exactly represent +1.0.  For an n-bit fixed-point component,  
      0 maps to -1.0, 2^(n-1) maps to 0.0, and 2^n-1 (maximum value)  
      maps to 1.0 - 1/(2^(n-1)).  This same conversion is applied to  
      stored textures using the signed texture types in NV_texture_shader.  
      This specification is written using the conventional OpenGL mapping  
      where -1.0 and +1.0 can be represented exactly, but 0.0 can not.  
      The specification is simpler and avoids precision-dependent language  
      describing the mapping.  We expect some leeway in how the remapping  
      is applied.  
      This issue is discussed in more detail in the issues section  
      of the NV_texture_shader specification (the question is phrased  
    (5) Are texture border color components remapped?  
      RESOLVED:  Yes -- if the border values are used for filtering,  
      border color components are remapped identically to normal texel  
homeprevnext New Procedures and Functions
homeprevnext New Tokens
    Accepted by the <pname> parameters of TexParameteri,  
    TexParameteriv, TexParameterf, TexParameterfv, GetTexParameteri,  
    and GetTexParameteriv:  
        TEXTURE_UNSIGNED_REMAP_MODE_NV               0x888F  
homeprevnext Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
homeprevnext Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
    Modify Section 3.8.4, Texture Parameters, p.135  
    (modify Table 3.19, p. 137)  
        Name                Type   Legal Values  
        -----------------   ----   ----------------------  
    Modify Section 3.8.8,  Texture Minification, p.140  
    (add after the last paragraph before the "Mipmapping" subsection,  
    p. 144)  
    After the texture filter is applied, the filtered texture values are  
    optionally rescaled, converting unsigned texture components encoded  
    in the range [0,1] to signed values in the range [-1,+1].  If the  
    the filtered values for each unsigned component of the texture is  
    transformed by  
        tau = 2 * tau - 1.  
    For components  
homeprevnext Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment Operations and the Frame Buffer)
homeprevnext Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
homeprevnext Additions to Chapter 6 of the OpenGL 1.4 Specification (State and State Requests)
homeprevnext Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
homeprevnext Additions to the AGL/GLX/WGL Specifications
homeprevnext GLX Protocol
homeprevnext Errors
homeprevnext New State
(add to table 6.15, p. 230)  
Get Value                       Type  Get Command        Value   Description         Sec.   Attribute  
------------------------------  ----  -----------------  ------- ------------------  -----  ---------  
TEXTURE_UNSIGNED_REMAP_MODE_NV  nxZ2  GetTexParameteriv  NONE    unsigned component  3.8.8  texture  
homeprevnext Revision History
Rev.    Date    Author   Changes  
----  -------- --------  --------------------------------------------  
 4    06/14/05  mjk      Add to-be-discontinued "Status" message and  
                         discussion of alternatives.  
 3    10/07/02  pbrown   Minor wording changes on precision issues -- this  
                         remapping should produce roughly the same results  
                         as storing the texture in signed form.  
 2    10/07/02  pbrown   Added issue about where the remapping is applied,  
                         and what happens to border colors.  
 1    10/07/02  pbrown   Initial revision.  
 1    10/07/02  pbrown   Initial revision.  
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