GLTEXENV() MachTen Programmer’s Manual GLTEXENV()

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 environ-
ment parameter. Accepted values are
GL_TEXTURE_ENV_MODE and GL_TEXTURE_ENV_COLOR.

params Specifies a pointer to a parameter array that con-
tains 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 environ-
ment 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, 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 $A sub t$.

center box tab(:) ; ci || ci s s s ci || c c c c c || c |
c | c | c. Base internal:Texture functions for-
mat: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:$C sub v = ( 1 - L sub t ) C sub f$:$C
sub v = L sub t$ 1: : :$+ L sub t C sub c$: : : : : : $A
sub v = A sub f$:: $A sub v = A sub f$:$A sub v = A sub f$
_ 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$
_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:$C sub v = ( 1 - I sub t ) C sub f$ :$C sub v
= I sub t$ : : :$+ I sub t C sub c$ : : : : :$A sub v = A
sub f I sub t$::$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$ 3: : : $+ C sub t C
sub c$ : : : : :$A sub v = A sub f$:$A sub v = A sub f$:$A
sub v = A sub f$:$A sub v = A sub f$ _ 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$ 4: :$+
A sub t C sub t$: $+ C sub t C sub c$ : : : : :$A sub v =
A sub t A sub f$:$A sub v = A sub f$:$A sub v = A sub t A
sub f$:$A sub v = A sub t$

If pname is GL_TEXTURE_ENV_COLOR, params is a pointer to
an array that holds an RGBA color consisting of four val-
ues. 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.

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.

ASSOCIATED GETS
glGetTexEnv

SEE ALSO
glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopy-
TexSubImage1D, glCopyTexSubImage2D, glTexImage1D, glTexIm-
age2D, glTexParameter, glTexSubImage1D, glTexSubImage2D

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