glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv - set texture environment parameters
void glTexEnvf( GLenum target, GLenum pname, GLfloat param ) void glTexEnvi( GLenum target, GLenum pname, GLint param )
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, or GL_BLEND.
void glTexEnvfv( GLenum target, GLenum pname, const GLfloat *params ) void glTexEnviv( GLenum target, GLenum pname, const GLint *params )
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 an array of parameters: 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. Three texture functions are defined:
GL_MODULATE, GL_DECAL, and GL_BLEND
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 and glTexImage2D). In a one-component image, L indicates
t
that single component. A two-component image uses L and A . A three-
t t
component image has only a color value, C . A four-component image has
t
both a color value C and an alpha value A .
t t
----------------------------------------------------------------
| number of || texture functions |
|components || GL_MODULATE GL_DECAL GL_BLEND |
----------------------------------------------------------------
| || C =L C | | C =(1-L )C +L C |
| 1 || v t f | undefined | v t f t c |
| || A =A | | A =A |
| || v f | | v f |
|-----------||------------|------------------|------------------|
| || C =L C | | C =(1-L )C +L C |
| 2 || v t f | undefined | v t f t c |
| || A =A A | | A =A A |
| || v t f | | v t f |
|-----------||------------|------------------|------------------|
| || C =C C | C =C | |
| 3 || v t f | v t | undefined |
| || A =A | A =A | |
| || v f | v f | |
|-----------||------------|------------------|------------------|
| || C =C C | C =(1-A )C +A C | |
| 4 || v t f | v t f t t | undefined |
| || A =A A | A =A | |
| || v t f | v 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 takes these four values.
c
GL_TEXTURE_ENV_MODE defaults to GL_MODULATE and GL_TEXTURE_ENV_COLOR
defaults to (0,0,0,0).
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
glTexImage1D, glTexImage2D, glTexParameter
Introduction | Alphabetic | Specification
Last Edited: Tue, May 23, 1995