gltexenv - Man Page
glTexEnv(3G) OpenGL Reference 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 texture
environment parameter. Must be GL_TEXTURE_ENV_MODE.
param Specifies a single symbolic constant, one of GL_MODULATE,
GL_DECAL, GL_BLEND, GL_REPLACE_EXT, or GL_ADD.
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, GL_TEXTURE_ENV_COLOR, and
GL_TEXTURE_ENV_BIAS_SGIX.
params
Specifies a pointer to an array of parameters: 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
GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COLOR, or GL_TEXTURE_ENV_BIAS_SGIX.
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glTexEnv(3G) OpenGL Reference glTexEnv(3G)
If pname is GL_TEXTURE_ENV_MODE, then params is (or points to) the
symbolic name of a texture function. Five texture functions may be
defined: GL_MODULATE, GL_DECAL, GL_BLEND, GL_REPLACE_EXT, and GL_ADD.
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 tables show how
the RGBA color is produced for each of the texture functions. 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, the
subscript b to the texture environment bias 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 and glTexImage2D). In an image of GL_LUMINANCE format Lt
indicates the single component. In an image of GL_ALPHA format At
indicates the single component. In an image of GL_INTENSITY format It
indicates the 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. If a color triple is
shown to be equal to a single component format, this denotes that each
component of the color triple is set equal to the single component.
Similarly when 2 color triples are shown as being multiplied, this
denotes that each component of the first triple is multiplied by the
corresponding component of the second triple.
________________________________________________________________________
| number of || texture functions |
|___________________||__________________________________________________|
| GL_LUMINANCE || Cv=LtCf | | Cv=(1-Lt)Cf+LtCc |
| 1 || Av=Af | undefined | Av=Af |
|___________________||____________|__________________|__________________|
| GL_ALPHA || Cv=Cf | undefined | Cv=Cf |
|___________________||____________|__________________|__________________|
| GL_INTENSITY || Cv=ItCf | | Cv=(1-It)Cf+ItCc |
| || Av=ItAf | undefined | Av=(1-It)Af+ItAc |
|___________________||____________|__________________|__________________|
|GL_LUMINANCE_ALPHA || Cv=LtCf | undefined | Cv=(1-Lt)Cf+LtCc |
|___________________||____________|__________________|__________________|
| GL_RGB || Cv=CtCf | Cv=Ct | Cv=(1-Ct)Cf+CtCc |
| 3 || Av=Af | Av=Af | Av=Af |
|___________________||____________|__________________|__________________|
| GL_RGBA || Cv=CtCf | Cv=(1-At)Cf+AtCt | Cv=(1-Ct)Cf+CtCc |
|___________________||____________|__________________|__________________|
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glTexEnv(3G) OpenGL Reference glTexEnv(3G)
______________________________________________________
| number of || texture functions |
|___________________||_______________________________|
| GL_LUMINANCE || Cv=Lt | Cv=Cf+LtCc+Cb |
| 1 || Av=Af | Av=Af |
|___________________||_______________|_______________|
| GL_ALPHA || Cv=Cf | Cv=Cf |
|___________________||_______________|_______________|
| GL_INTENSITY || Cv=It | Cv=Cf+ItCc+Cb |
| || Av=It | Av=Af+ItAc+Ab |
|___________________||_______________|_______________|
|GL_LUMINANCE_ALPHA || Cv=Lt | Cv=Cf+LtCc+Cb |
|___________________||_______________|_______________|
| GL_RGB || Cv=Ct | Cv=Cf+CtCc+Cb |
| 3 || Av=Af | Av=Af |
|___________________||_______________|_______________|
| GL_RGBA || Cv=Ct | Cv=Cf+CtCc+Cb |
|___________________||_______________|_______________|
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.
If pname is GL_TEXTURE_ENV_BIAS_SGIX, 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. Cb takes these four
values.
GL_TEXTURE_ENV_MODE defaults to GL_MODULATE, GL_TEXTURE_ENV_COLOR
defaults to (0,0,0,0), and GL_TEXTURE_ENV_BIAS_SGIX defaults to
(0,0,0,0).
NOTES
GL_REPLACE_EXT is part of the EXT_texture extension. GL_ADD and
GL_TEXTURE_ENV_BIAS_SGIX are part of the SGIX_texture_add_env extension.
See glIntro for more information concerning extensions.
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.
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glTexEnv(3G) OpenGL Reference glTexEnv(3G)
ASSOCIATED GETS
glGetTexEnv
MACHINE DEPENDENCIES
RealityEngine, RealityEngine2, and VTX and High Impact and Maximum Impact
systems do not support GL_REPLACE_EXT.
The SGIX_texture_add_env extension is supported only on InfiniteReality
systems. There is a significant restriction on the texture environment
bias color, however. Only two values are allowed for the bias: zero, or
exactly -0.5 times the texture environment color. (This makes the
expression CtCc+Cb equivalent to CtCc or (Ct-0.5)Cc, respectively.)
SEE ALSO
glTexImage1D, glTexImage2D, glTexParameter
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