GLTEXENV()GLTEXENV()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 )
delim $$
PARAMETERS
target Specifies a texture environment. Must be GL_TEXTURE_ENV.
pname Specifies the symbolic name of a single-valued texture environ‐
ment 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_TEX‐
TURE_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 GL_TEXTURE_ENV_COLOR.
If pname is GL_TEXTURE_ENV_MODE, then params is (or points to) the sym‐
bolic name of a texture function. Four texture functions may be speci‐
fied: GL_MODULATE, GL_DECAL, GL_BLEND, and GL_REPLACE.
A texture function acts on the fragment to be textured using the tex‐
ture image value that applies to the fragment (see glTexParameter) and
produces an RGBA color for that fragment. The following table shows
how the RGBA color is produced 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 frag‐
ment, 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, glCopyTexImage1D, and glCopyTexImage2D).
In a one-component image, $L sub t$ indicates that single component. A
two-component image uses $L sub t$ and $A sub t$. A three-component
image has only a color value, $C sub t$. A four-component image has
both a color value $C sub t$ and an alpha value $A sub t$.
┌──────────────┬┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│Base internal ││ Texture functions │
│ format ││ GL_MODULATE GL_DECAL GL_BLEND GL_REPLACE │
├──────────────┼┼────────────────────────────┬──────────────────────────────────────┬──────────────────────────────────────┬─────────────────────┤
│ GL_ALPHA ││ $C sub v = C sub f$ │ undefined │ $C sub v = C sub f$ │ $C sub v = C sub f$ │
│ ││$A sub v = A sub f A sub t$ │ │ $A sub v = A sub f$ │ $A sub v = A sub t$ │
├──────────────┼┼────────────────────────────┼──────────────────────────────────────┼──────────────────────────────────────┼─────────────────────┤
│GL_LUMINANCE ││$C sub v = L sub t C sub f$ │ undefined │ $C sub v = ( 1 - L sub t ) C sub f$ │ $C sub v = L sub t$ │
│ 1 ││ │ │ $+ L sub t C sub c$ │ │
│ ││ │ │ │ │
│ ││ $A sub v = A sub f$ │ │ $A sub v = A sub f$ │ $A sub v = A sub f$ │
├──────────────┼┼────────────────────────────┼──────────────────────────────────────┼──────────────────────────────────────┼─────────────────────┤
│GL_LUMINANCE ││$C sub v = L sub t C sub f$ │ undefined │ $C sub v = ( 1 - L sub t ) C sub f $ │ $C sub v = L sub t$ │
│ \f3_ALPHA ││ │ │ $+ L sub t C sub c$ │ │
│ 2 ││ │ │ │ │
│ ││$A sub v = A sub t A sub f$ │ │ $A sub v = A sub t A sub f$ │ $A sub v = A sub t$ │
├──────────────┼┼────────────────────────────┼──────────────────────────────────────┼──────────────────────────────────────┼─────────────────────┤
│GL_INTENSITY ││$C sub v = C sub f I sub t$ │ undefined │ $C sub v = ( 1 - I sub t ) C sub f$ │ $C sub v = I sub t$ │
│ ││ │ │ $+ I sub t C sub c$ │ │
│ ││ │ │ │ │
│ ││$A sub v = A sub f I sub t$ │ │ $A sub v = ( 1 - I sub t ) A sub f $ │ $A sub v = I sub t$ │
│ ││ │ │ $+ I sub t A sub c$ │ │
├──────────────┼┼────────────────────────────┼──────────────────────────────────────┼──────────────────────────────────────┼─────────────────────┤
│ GL_RGB ││$C sub v = C sub t C sub f$ │ $C sub v = C sub t$ │ $C sub v = (1 - C sub t) C sub f $ │ $C sub v = C sub t$ │
│ 3 ││ │ │ $+ C sub t C sub c$ │ │
│ ││ │ │ │ │
│ ││ $A sub v = A sub f$ │ $A sub v = A sub f$ │ $A sub v = A sub f$ │ $A sub v = A sub f$ │
├──────────────┼┼────────────────────────────┼──────────────────────────────────────┼──────────────────────────────────────┼─────────────────────┤
│ GL_RGBA ││$C sub v = C sub t C sub f$ │ $C sub v = ( 1 - A sub t ) C sub f $ │ $C sub v = (1 - C sub t) C sub f $ │ $C sub v = C sub t$ │
│ 4 ││ │ $+ A sub t C sub t$ │ $+ C sub t C sub c$ │ │
│ ││ │ │ │ │
│ ││$A sub v = A sub t A sub f$ │ $A sub v = A sub f$ │ $A sub v = A sub t A sub f$ │ $A sub v = A sub t$ │
└──────────────┴┴────────────────────────────┴──────────────────────────────────────┴──────────────────────────────────────┴─────────────────────┘
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 compo‐
nents 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. $C sub c$ 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.
ERRORS
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 execution of glEnd.
ASSOCIATED GETS
glGetTexEnv
SEE ALSO
glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D,
glCopyTexSubImage2D, glTexImage1D, glTexImage2D, glTexParameter, glTex‐
SubImage1D, glTexSubImage2D
GLTEXENV()
