glTexEnv(3G)glTexEnv(3G)NAME
glTexEnv, glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv - set texture
environment parameters
SYNOPSIS
void glTexEnvf(
GLenum target,
GLenum pname,
GLfloat param ); void glTexEnvi(
GLenum target,
GLenum pname,
GLint param );
PARAMETERS
Specifies a texture environment. Must be GL_TEXTURE_ENV. Specifies the
symbolic name of a single-valued texture environment parameter. Must be
GL_TEXTURE_ENV_MODE. Specifies a single symbolic constant, one of
GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE.
SYNOPSIS
void glTexEnvfv(
GLenum target,
GLenum pname,
const GLfloat *params ); void glTexEnviv(
GLenum target,
GLenum pname,
const GLint *params );
PARAMETERS
Specifies a texture environment. Must be GL_TEXTURE_ENV. Specifies the
symbolic name of a texture environment parameter. Accepted values are
GL_TEXTURE_ENV_MODE and GL_TEXTURE_ENV_COLOR. 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 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, L[t] indicates that sin‐
gle component. A two-component image uses L[t] and A[t]. A three-compo‐
nent image has only a color value, C[t]. A four-component image has
both a color value C[t] and an alpha value A[t].
────────────────────────────────────────────────────────────────────────────
Base inter‐ Texture Functions
nal
format GL_MODULATE GL_DECAL GL_BLEND GL_REPLACE
────────────────────────────────────────────────────────────────────────────
GL_ALPHA C[v] = undefined C[v] = C[v] =
C[f]A[v] = C[f]A[v] = A[f] C[f]A[v] =
A[f] A[t] A[t]
GL_LUMI‐ C[v] = L[t] undefined C[v] = ( 1 - C[v] = L[t]
NANCE (or C[f] A[v] = L[t] ) C[f] + A[v] = A[f]
1) A[f] L[t] C[c]
A[v] = A[f]
GL_LUMI‐ C[v] = L[t] undefined C[v] = ( 1 - C[v] = L[t]
NANCE_ALPHA C[f] A[v] = L[t] ) C[f] A[v] = A[t]
(or 2) A[t] A[f] + L[t] C[c]
A[v] = A[t]
A[f]
GL_INTEN‐ C[v] = C[f] undefined C[v] = ( 1 - C[v] = I[t]
SITY I[t] A[v] = I[t] ) C[f] + A[v] = I[t]
A[f] I[t] I[t] C[c] A[v]
= ( 1 - I[t] )
A[f] + I[t]
A[c]
GL_RGB (or C[v] = C[t] C[v] = C[t] C[v] = (1 - C[v] = C[t]
3) C[f] A[v] = A[v] = A[f] C[t]) C[f] + A[v] = A[f]
A[f] C[t] C[c] A[v]
= A[f]
GL_RGBA (or C[v] = C[t] C[v] = ( 1 C[v] = (1 - C[v] = C[t]
4) C[f] A[v] = - A[t]) C[t]) C[f] A[v] = A[t]
A[t] A[f] C[f] + A[t] + C[t] C[c]
C[t] A[v] = A[v] = A[t]
A[f] A[f]
────────────────────────────────────────────────────────────────────────────
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. C[c] takes these four val‐
ues.
GL_TEXTURE_ENV_MODE defaults to GL_MODULATE andGL_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() con‐
trols the texture environment for the current active texture unit,
selected byglActiveTextureARB(). 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 GETSglGetTexEnv()SEE ALSOglActiveTextureARB(3), glCopyPixels(3), glCopyTexImage1D(3), glCopyTex‐
Image2D(3), glCopyTexSubImage1D(3), glCopyTexSubImage2D(3), glCopyTex‐
SubImage3D(3), glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glT‐
exParameter(3), glTexSubImage1D(3), glTexSubImage2D(3), glTexSubIm‐
age3D(3)glTexEnv(3G)