xref: /third_party/openGLES/extensions/ATI/ATI_texture_mirror_once.txt

Name

    ATI_texture_mirror_once

Name Strings

    GL_ATI_texture_mirror_once

Contact

    Dan Ginsburg, AMD (dan.ginsburg 'at' amd.com)

Version

    Last Modified Date: 11/4/2006 Revision: 0.31

Number

    221

Dependencies

    EXT_texture3D

Overview

    ATI_texture_mirror_once extends the set of texture wrap modes to 
    include two modes (GL_MIRROR_CLAMP_ATI, GL_MIRROR_CLAMP_TO_EDGE_ATI) 
    that effectively use a texture map twice as large as the original image 
    in which the additional half of the new image is a mirror image of the 
    original image.

    This new mode relaxes the need to generate images whose opposite edges
    match by using the original image to generate a matching "mirror image".
    This mode allows the texture to be mirrored only once in the negative
    s, t, and r directions.

Issues

    None known

New Procedure and Functions

    None

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_EXT:

      MIRROR_CLAMP_ATI                     0x8742
      MIRROR_CLAMP_TO_EDGE_ATI             0x8743

Additions to Chapter 2 of the OpenGL 1.2.1 Specification (Operation)

    None

Additions to Chapter 3 if the OpenGL 1.2.1 Specification (Rasterization):

  - (3.8.3, p. 124) Change first three entries in table:

    "TEXTURE_WRAP_S     integer     CLAMP, CLAMP_TO_EDGE, REPEAT, 
                                    MIRROR_CLAMP_ATI, MIRROR_CLAMP_TO_EDGE_ATI
     TEXTURE_WRAP_T     integer     CLAMP, CLAMP_TO_EDGE, REPEAT, 
                                    MIRROR_CLAMP_ATI, MIRROR_CLAMP_TO_EDGE_ATI
     TEXTURE_WRAP_R     integer     CLAMP, CLAMP_TO_EDGE, REPEAT, 
                                    MIRROR_CLAMP_ATI, MIRROR_CLAMP_TO_EDGE_ATI"

  - (3.8.4, p. 125) Added after second paragraph:

    "If TEXTURE_WRAP_S, TEXTURE_WRAP_T, or TEXTURE_WRAP_R_EXT is set to
     MIRROR_CLAMP_ATI or MIRROR_CLAMP_TO_EDGE_ATI, the s (or t or r) 
     coordinate is clamped to [-1, 1] and then converted to:

         s      0  <= s <= 1
        -s     -1  <= s <  0

     Like the CLAMP wrap mode, with MIRROR_CLAMP_ATI the texels from 
     the border can be used by the texture filter.  MIRROR_CLAMP_TO_EDGE_ATI 
     clamps texture coordinates at all mipmap levels such that the texture 
     filter never samples a border texel."

  - (3.8.5, p.127) Change last paragraph to:

    "When TEXTURE_MIN_FILTER is LINEAR, a 2 x 2 x 2 cube of texels in the
     image array of level TEXTURE_BASE_LEVEL is selected.  This cube is 
     obtained by first clamping texture coordinates as described above 
     under Texture Wrap Modes (if the wrap mode for a coordinate is CLAMP,
     CLAMP_TO_EDGE, MIRROR_CLAMP_ATI, or MIRROR_CLAMP_TO_EDGE_ATI) and 
     computing..."


Additions to Chapter 4:

    None

Additions to Chapter 5:

    None

Additions to Chapter 6:

    None

Additions to the GLX Specification

    None

GLX Protocol

    None

Errors

    None

Dependencies on EXT_texture3D

    If EXT_texture3D is not implemented, then the references to clamping of 3D
    textures in this file are invalid, and references to TEXTURE_WRAP_R_EXT
    should be ignored.


New State

    Only the type information changes for these parameters:

    Get Value           Get Command             Type    Initial Value   Attrib
    ---------           -----------             ----    -------------   ------
    TEXTURE_WRAP_S      GetTexParameteriv       n x Z5  REPEAT          texture
    TEXTURE_WRAP_T      GetTexParameteriv       n x Z5  REPEAT          texture
    TEXTURE_WRAP_R_EXT  GetTexParameteriv       n x Z5  REPEAT          texture

New Implementation Dependent State

    None