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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