MirOS Manual: glTexEnv(3), glTexEnvf(3), glTexEnvfv(3), glTexEnvi(3), glTexEnviv(3)


GLTEXENV(3G)        UNIX Programmer's Manual         GLTEXENV(3G)

NAME

     glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv - set texture
     environment parameters

C SPECIFICATION

     void glTexEnvf( GLenum target,
                     GLenum pname,
                     GLfloat param )
     void glTexEnvi( GLenum target,
                     GLenum pname,
                     GLint param )

PARAMETERS

     target  Specifies a texture environment. Must be
             GL_TEXTURE_ENV.

     pname   Specifies the symbolic name of a single-valued tex-
             ture environment parameter. Must be
             GL_TEXTURE_ENV_MODE.

     param   Specifies a single symbolic constant, one of
             GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE.

C SPECIFICATION

     void glTexEnvfv( GLenum target,
                      GLenum pname,
                      const GLfloat *params )
     void glTexEnviv( GLenum target,
                      GLenum pname,
                      const GLint *params )

PARAMETERS

     target
          Specifies a texture environment. Must be
          GL_TEXTURE_ENV.

     pname
          Specifies the symbolic name of a texture environment
          parameter. Accepted values are GL_TEXTURE_ENV_MODE and
          GL_TEXTURE_ENV_COLOR.

     params
          Specifies a pointer to a parameter array that contains
          either a single symbolic constant or an RGBA color.

DESCRIPTION

     A texture environment specifies how texture values are
     interpreted when a fragment is textured. target must be
     GL_TEXTURE_ENV. pname can be either GL_TEXTURE_ENV_MODE or

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     GL_TEXTURE_ENV_COLOR.

     If pname is GL_TEXTURE_ENV_MODE, then params is (or points
     to) the symbolic name of a texture function. Four texture
     functions may be specified: GL_MODULATE, GL_DECAL, GL_BLEND,
     and GL_REPLACE.

     A texture function acts on the fragment to be textured using
     the texture image value that applies to the fragment (see
     glTexParameter) and produces an RGBA color for that frag-
     ment. The following table shows how the RGBA color is pro-
     duced for each of the three texture functions that can be
     chosen. C is a triple of color values (RGB) and A is the
     associated alpha value. RGBA values extracted from a texture
     image are in the range [0,1]. The subscript f refers to the
     incoming fragment, the subscript t to the texture image, the
     subscript c to the texture environment color, and subscript
     v indicates a value produced by the texture function.

     A texture image can have up to four components per texture
     element (see glTexImage1D, glTexImage2D, glTexImage3D,
     glCopyTexImage1D, and glCopyTexImage2D). In a one-component
     image, Lt indicates that single component. A two-component
     image uses Lt and At. A three-component image has only a
     color value, Ct. A four-component image has both a color
     value Ct and an alpha value At.

_______________________________________________________________________

    Base internal                   Texture functions
                         GL_MODULATE   GL_DECAL   GL_BLEND   GL_REPLACE

_______________________________________________________________________

GL_ALPHA:Cv = Cf:undefined:Cv = Cf:Cv = Cf
:Av = AfAt::Av = Af:Av = At

_______________________________________________________________________

GL_LUMINANCE:Cv = LtCf:undefined:Cv = (1-Lt)Cf:Cv = Lt
     : : :+LtCc:
1: Av = Af:: Av = Af:Av = Af

_______________________________________________________________________

GL_LUMINANCE:Cv = LtCf:undefined:Cv = (1-Lt)Cf:Cv = Lt

_ALPHA: : : +LtCc

2:Av = AtAf::Av = AtAf:Av = At

_______________________________________________________________________

GL_INTENSITY:Cv = CfIt:undefined:Cv = (1-It)Cf :Cv = It
      : : :+ItCc
c :Av = AfIt::Av = (1-It)Af:Av = It
     : : :+ItAc:

_______________________________________________________________________

GL_RGB:Cv = CtCf:Cv = Ct:Cv = (1-Ct)Cf:Cv = Ct
     : : : +CtCc
3:Av = Af:Av = Af:Av = Af:Av = Af

_______________________________________________________________________

GL_RGBA:Cv = CtCf:Cv = (1-At)Cf:Cv = (1-Ct)Cf:Cv = Ct

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   : :+AtCt: +CtCc
4:Av = AtAf:Av = Af:Av = AtAf:Av = At

_______________________________________________________________________


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     If pname is GL_TEXTURE_ENV_COLOR, params is a pointer to an
     array that holds an RGBA color consisting of four values.
     Integer color components are interpreted linearly such that
     the most positive integer maps to 1.0, and the most negative
     integer maps to -1.0. The values are clamped to the range
     [0,1] when they are specified. Cc takes these four values.

     GL_TEXTURE_ENV_MODE defaults to GL_MODULATE and
     GL_TEXTURE_ENV_COLOR defaults to (0, 0, 0, 0).

NOTES

     GL_REPLACE may only be used if the GL version is 1.1 or
     greater.

     Internal formats other than 1, 2, 3, or 4 may only be used
     if the GL version is 1.1 or greater.

     When the GL_ARB_multitexture extension is supported,
     glTexEnv controls the texture environment for the current
     active texture unit, selected by glActiveTextureARB.
     GL_INVALID_ENUM is generated when target or pname is not one
     of the accepted defined values, or when params should have a
     defined constant value (based on the value of pname) and
     does not.

     GL_INVALID_OPERATION is generated if glTexEnv is executed
     between the execution of glBegin and the corresponding exe-
     cution of glEnd.

ASSOCIATED GETS

     glGetTexEnv

SEE ALSO

     glActiveTextureARB(3G), glCopyPixels(3G),
     glCopyTexImage1D(3G), glCopyTexImage2D(3G),
     glCopyTexSubImage1D(3G), glCopyTexSubImage2D(3G),
     glCopyTexSubImage3D(3G), glTexImage1D(3G), glTexImage2D(3G),
     glTexImage3D(3G), glTexParameter(3G), glTexSubImage1D(3G),
     glTexSubImage2D(3G), glTexSubImage3D(3G)

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