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 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
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,
$L sub t$ 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
|
| 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 | $C sub v ~=~ ( 1 - L sub t ) C sub f$ | $C sub v ~=~ L sub t$
|
| | | $+ L sub t C sub c$ |
|
| 1 | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub f$ |
|
| 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 | $C sub v ~=~ ( 1 - I sub t ) C sub f$ | $C sub v ~=~ I sub t$
|
| | | $+ I sub t C sub c$ |
|
| 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 $ | $C sub v ~=~ C sub t$
|
| | | $+ C sub t C sub c$ |
|
| 3 | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub f$
|
|
| 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 $ | $C sub v ~=~ C sub t$
|
| | $+ A sub t C sub t$ | $+ C sub t C sub c$ |
|
| 4 | $A sub v ~=~ A sub t A sub f$ | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub t A sub f$ | $A sub v ~=~ A sub t$
|
|
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 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.
$C sub c$ 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.
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 execution 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)
Index
- NAME
-
- C SPECIFICATION
-
- PARAMETERS
-
- C SPECIFICATION
-
- PARAMETERS
-
- DESCRIPTION
-
- NOTES
-
- ASSOCIATED GETS
-
- SEE ALSO
-
