glTexEnv, glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv -
set texture environment parameters
void glTexEnvf(
GLenum target,
GLenum pname,
GLfloat param ); void glTexEnvi(
GLenum target,
GLenum pname,
GLint param );
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.
void glTexEnvfv(
GLenum target,
GLenum pname,
const GLfloat *params ); void glTexEnviv(
GLenum target,
GLenum pname,
const GLint *params );
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.
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 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
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 single component.
A two-component image uses L[t] and A[t]. A three-component
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 values.
GL_TEXTURE_ENV_MODE defaults to GL_MODULATE andGL_TEXTURE_ENV_COLOR
defaults to (0, 0, 0, 0).
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 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().
glGetTexEnv()
glActiveTextureARB(3), glCopyPixels(3), glCopyTexImage1D(3), glCopyTexImage2D(3), glCopyTexSubImage1D(3),
glCopyTexSubImage2D(3), glCopyTexSubImage3D(3), glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glTexParameter(3), glTexSubImage1D(3), glTexSubImage2D(3), glTexSubImage3D(3)
glTexEnv(3G)
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