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GL_EXT_texture_edge_clamp
homeprevnext Name
  
    EXT_texture_edge_clamp  
  
homeprevnext Name Strings
  
    GL_EXT_texture_edge_clamp  
  
homeprevnext Version
  
    $Date: 1997/09/22 23:04:01 $ $Revision: 1.1 $  
  
homeprevnext Dependencies
  
    SGIS_texture_filter4 affects the definition of this extension  
  
homeprevnext Overview
  
    The base OpenGL provides clamping such that the texture coordinates are  
    limited to exactly the range [0,1].  When a texture coordinate is  
    clamped using this algorithm, the texture sampling filter straddles the  
    edge of the texture image, taking 1/2 its sample values from within the  
    texture image, and the other 1/2 from the texture border.  It is  
    sometimes desirable to clamp a texture without requiring a border, and  
    without using the constant border color.  
  
    This extension defines a new texture clamping algorithm.  
    CLAMP_TO_EDGE_EXT clamps texture coordinates at all mipmap levels such  
    that the texture filter never samples a border texel.  When used with a  
    NEAREST or a LINEAR filter, the color returned when clamping is derived  
    only from texels at the edge of the texture image.  When used with  
    FILTER4 filters, the filter operations of CLAMP_TO_EDGE_EXT are defined  
    but don't result in a nice clamp-to-edge color.  
  
    CLAMP_TO_EDGE_EXT is supported by 1, 2, and 3-dimensional textures  
    only.  
  
homeprevnext Issues
  
    *   Is the arithmetic for FILTER4 filters correct?  Is this the right  
        thing to do?  
  
homeprevnext New Procedures and Functions
  
    None  
  
homeprevnext New Tokens
  
    Accepted by the <param> parameter of TexParameteri and TexParameterf,  
    and by the <params> parameter of TexParameteriv and TexParameterfv, when  
    their <pname> parameter is TEXTURE_WRAP_S, TEXTURE_WRAP_T, or  
    TEXTURE_WRAP_R:  
  
        CLAMP_TO_EDGE_EXT               0x812F  
  
homeprevnext Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
  
    None  
  
homeprevnext Additions to Chapter 3 of the 1.0 Specification (Rasterization)
  
    GL Specification Table 3.7 is updated as follows:  
  
        Name                            Type        Legal Values  
        ----                            ----        ------------  
        TEXTURE_WRAP_S                  integer     CLAMP, REPEAT,  
                                                    CLAMP_TO_EDGE_EXT  
        TEXTURE_WRAP_T                  integer     CLAMP, REPEAT,  
                                                    CLAMP_TO_EDGE_EXT  
        TEXTURE_WRAP_R                  integer     CLAMP, REPEAT,  
                                                    CLAMP_TO_EDGE_EXT  
        TEXTURE_MIN_FILTER              integer     NEAREST, LINEAR,  
                                                    NEAREST_MIPMAP_NEAREST,  
                                                    NEAREST_MIPMAP_LINEAR,  
                                                    LINEAR_MIPMAP_NEAREST,  
                                                    LINEAR_MIPMAP_LINEAR,  
                                                    FILTER4_SGIS,  
                                                    LINEAR_CLIPMAP_LINEAR_SGIX  
        TEXTURE_MAG_FILTER              integer     NEAREST, LINEAR,  
                                                    FILTER4_SGIS,  
                                                    LINEAR_DETAIL_SGIS,  
                                                    LINEAR_DETAIL_ALPHA_SGIS,  
                                                    LINEAR_DETAIL_COLOR_SGIS,  
                                                    LINEAR_SHARPEN_SGIS,  
                                                    LINEAR_SHARPEN_ALPHA_SGIS,  
                                                    LINEAR_SHARPEN_COLOR_SGIS,  
                                                    LINEAR_LEQUAL_R_SGIS,  
                                                    LINEAR_GEQUAL_R_SGIS  
        TEXTURE_BORDER_COLOR            4 floats    any 4 values in [0,1]  
        DETAIL_TEXTURE_LEVEL_SGIS       integer     any non-negative integer  
        DETAIL_TEXTURE_MODE_SGIS        integer     ADD, MODULATE  
        TEXTURE_MIN_LOD                 float       any value  
        TEXTURE_MAX_LOD                 float       any value  
        TEXTURE_BASE_LEVEL              integer     any non-negative integer  
        TEXTURE_MAX_LEVEL               integer     any non-negative integer  
        GENERATE_MIPMAP_SGIS            boolean     TRUE or FALSE  
        TEXTURE_CLIPMAP_OFFSET_SGIX     2 floats    any 2 values  
  
        Table 3.7: Texture parameters and their values.  
  
    CLAMP_TO_EDGE_EXT texture clamping is specified by calling  
    TexParameteri with <target> set to TEXTURE_1D, TEXTURE_2D, or  
    TEXTURE_3D, <pname> set to TEXTURE_WRAP_S, TEXTURE_WRAP_T,  
    or TEXTURE_WRAP_R, and <param> set to CLAMP_TO_EDGE_EXT.  
  
    Let [min,max] be the range of a clamped texture coordinate, and let N  
    be the size of the 1D, 2D, or 3D texture image in the direction of  
    clamping.  Then in all cases  
  
        max = 1 - min  
  
    because the clamping is always symmetric about the [0,1] mapped range of  
    a texture coordinate.  When used with NEAREST or LINEAR filters,  
    CLAMP_TO_EDGE_EXT defines a minimum clamping value of  
  
        min = 1 / 2*N  
  
    When used with FILTER4 filters, CLAMP_TO_EDGE_EXT defines a minimum  
    clamping value of  
  
        min = 3 / 2*N,          N > 2  
  
        min = 1/2               N <= 2  
  
homeprevnext Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the Framebuffer)
  
    None  
  
homeprevnext Additions to Chapter 5 of the 1.0 Specification (Special Functions)
  
    None  
  
homeprevnext Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
  
    None  
  
homeprevnext Additions to the GLX Specification
  
    None  
  
homeprevnext Dependencies on SGIS_texture_filter4
  
    If SGIS_texture_filter4 is not implemented, then discussions about the  
    interaction of filter4 texture filters and the clamping function  
    described in this file are invalid, and should be ignored.  
  
homeprevnext Errors
  
    None  
  
homeprevnext New State
  
    Only the type information changes for these parameters:  
  
    Get Value           Get Command             Type    Initial Value   Attrib  
    ---------           -----------             ----    -------------   ------  
    TEXTURE_WRAP_S      GetTexParameteriv       n x Z3  REPEAT          texture  
    TEXTURE_WRAP_T      GetTexParameteriv       n x Z3  REPEAT          texture  
    TEXTURE_WRAP_R      GetTexParameteriv       n x Z3  REPEAT          texture  
  
homeprevnext New Implementation Dependent State
  
    None  
  
  
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