glTexEnv — 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.
May be GL_TEXTURE_ENV
, GL_TEXTURE_FILTER_CONTROL
or GL_POINT_SPRITE
.
pname
Specifies the symbolic name of a single-valued texture environment parameter.
May be either GL_TEXTURE_ENV_MODE
, GL_TEXTURE_LOD_BIAS
,
GL_COMBINE_RGB
,
GL_COMBINE_ALPHA
,
GL_SRC0_RGB
,
GL_SRC1_RGB
,
GL_SRC2_RGB
,
GL_SRC0_ALPHA
,
GL_SRC1_ALPHA
,
GL_SRC2_ALPHA
,
GL_OPERAND0_RGB
,
GL_OPERAND1_RGB
,
GL_OPERAND2_RGB
,
GL_OPERAND0_ALPHA
,
GL_OPERAND1_ALPHA
,
GL_OPERAND2_ALPHA
,
GL_RGB_SCALE
,
GL_ALPHA_SCALE
, or
GL_COORD_REPLACE
.
param
Specifies a single symbolic constant, one of GL_ADD
,
GL_ADD_SIGNED
, GL_INTERPOLATE
, GL_MODULATE
, GL_DECAL
,
GL_BLEND
, GL_REPLACE
, GL_SUBTRACT
, GL_COMBINE
,
GL_TEXTURE
, GL_CONSTANT
, GL_PRIMARY_COLOR
, GL_PREVIOUS
,
GL_SRC_COLOR
, GL_ONE_MINUS_SRC_COLOR
, GL_SRC_ALPHA
,
GL_ONE_MINUS_SRC_ALPHA
,
a single boolean value for the point sprite texture coordinate replacement,
a single floating-point value for the texture level-of-detail bias,
or 1.0, 2.0, or 4.0 when specifying the GL_RGB_SCALE
or GL_ALPHA_SCALE
.
void glTexEnvfv( | GLenum target, |
GLenum pname, | |
const GLfloat * params) ; |
void glTexEnviv( | GLenum target, |
GLenum pname, | |
const GLint * params) ; |
target
Specifies a texture environment.
May be either GL_TEXTURE_ENV
, or GL_TEXTURE_FILTER_CONTROL
.
pname
Specifies the symbolic name of a texture environment parameter.
Accepted values are GL_TEXTURE_ENV_MODE
, GL_TEXTURE_ENV_COLOR
, or
GL_TEXTURE_LOD_BIAS
.
params
Specifies a pointer to a parameter array that contains either a single symbolic constant, single floating-point number, or an RGBA color.
A texture environment specifies how texture values are interpreted when a
fragment is textured. When target
is GL_TEXTURE_FILTER_CONTROL
,
pname
must be GL_TEXTURE_LOD_BIAS
. When target
is
GL_TEXTURE_ENV
, pname
can be GL_TEXTURE_ENV_MODE
,
GL_TEXTURE_ENV_COLOR
, GL_COMBINE_RGB
, GL_COMBINE_ALPHA
,
GL_RGB_SCALE
, GL_ALPHA_SCALE
,
GL_SRC0_RGB
, GL_SRC1_RGB
, GL_SRC2_RGB
,
GL_SRC0_ALPHA
, GL_SRC1_ALPHA
, or GL_SRC2_ALPHA
.
If pname
is GL_TEXTURE_ENV_MODE
,
then params
is (or points to) the symbolic name of a texture function.
Six texture functions may be specified:
GL_ADD
,
GL_MODULATE
,
GL_DECAL
,
GL_BLEND
,
GL_REPLACE
, or
GL_COMBINE
.
The following table shows the correspondence of filtered texture
values
Texture Base Internal Format |
|
|
---|---|---|
GL_ALPHA
| (0, 0, 0) |
|
GL_LUMINANCE
|
(
| 1 |
GL_LUMINANCE_ALPHA
|
(
|
|
GL_INTENSITY
|
(
|
|
GL_RGB
|
(
| 1 |
GL_RGBA
|
(
|
|
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 first five texture functions that can be chosen.
Texture Base Internal Format |
Value
|
GL_REPLACE Function
|
GL_MODULATE Function
|
GL_DECAL Function
|
GL_BLEND Function
|
GL_ADD Function
|
---|---|---|---|---|---|---|
GL_ALPHA
|
|
|
| undefined |
|
|
|
|
|
|
| ||
GL_LUMINANCE
|
|
|
| undefined |
|
|
(or 1) |
|
|
|
|
| |
GL_LUMINANCE_ALPHA
|
|
|
| undefined |
|
|
(or 2) |
|
|
|
|
| |
GL_INTENSITY
|
|
|
| undefined |
|
|
|
|
|
|
| ||
GL_RGB
|
|
|
|
|
|
|
(or 3) |
|
|
|
|
|
|
GL_RGBA
|
|
|
|
|
|
|
(or 4) |
|
|
|
|
|
|
If pname
is GL_TEXTURE_ENV_MODE
, and params
is GL_COMBINE
, the
form of the texture function depends on the values of GL_COMBINE_RGB
and GL_COMBINE_ALPHA
.
The following describes how the texture sources, as specified by
GL_SRC0_RGB
, GL_SRC1_RGB
, GL_SRC2_RGB
,
GL_SRC0_ALPHA
, GL_SRC1_ALPHA
, and GL_SRC2_ALPHA
,
are combined to produce a final texture color. In the following tables,
GL_SRC0_c
is represented by
GL_SRC1_c
is
represented by
GL_SRC2_c
is represented by
GL_COMBINE_RGB
accepts any of GL_REPLACE
, GL_MODULATE
,
GL_ADD
, GL_ADD_SIGNED
, GL_INTERPOLATE
, GL_SUBTRACT
,
GL_DOT3_RGB
, or GL_DOT3_RGBA
.
GL_COMBINE_RGB
| Texture Function |
---|---|
GL_REPLACE
|
|
GL_MODULATE
|
|
GL_ADD
|
|
GL_ADD_SIGNED
|
|
GL_INTERPOLATE
|
|
GL_SUBTRACT
|
|
GL_DOT3_RGB
or
GL_DOT3_RGBA
|
|
The scalar results for GL_DOT3_RGB
and GL_DOT3_RGBA
are placed
into each of the 3 (RGB) or 4 (RGBA) components on output.
Likewise, GL_COMBINE_ALPHA
accepts any of GL_REPLACE
,
GL_MODULATE
, GL_ADD
, GL_ADD_SIGNED
, GL_INTERPOLATE
, or
GL_SUBTRACT
. The following table describes how alpha values are
combined:
GL_COMBINE_ALPHA
| Texture Function |
---|---|
GL_REPLACE
|
|
GL_MODULATE
|
|
GL_ADD
|
|
GL_ADD_SIGNED
|
|
GL_INTERPOLATE
|
|
GL_SUBTRACT
|
|
In the following tables, the value
The following table describes the values assigned to
GL_SRCn_RGB
|
GL_OPERANDn_RGB
| Argument Value |
---|---|---|
GL_TEXTURE
|
GL_SRC_COLOR
|
|
GL_ONE_MINUS_SRC_COLOR
|
| |
GL_SRC_ALPHA
|
| |
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_TEXTUREn
|
GL_SRC_COLOR
|
|
GL_ONE_MINUS_SRC_COLOR
|
| |
GL_SRC_ALPHA
|
| |
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_CONSTANT
|
GL_SRC_COLOR
|
|
GL_ONE_MINUS_SRC_COLOR
|
| |
GL_SRC_ALPHA
|
| |
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_PRIMARY_COLOR
|
GL_SRC_COLOR
|
|
GL_ONE_MINUS_SRC_COLOR
|
| |
GL_SRC_ALPHA
|
| |
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_PREVIOUS
|
GL_SRC_COLOR
|
|
GL_ONE_MINUS_SRC_COLOR
|
| |
GL_SRC_ALPHA
|
| |
GL_ONE_MINUS_SRC_ALPHA
|
|
For GL_TEXTUREn
sources,
The follow table describes the values assigned to
GL_SRCn_ALPHA
|
GL_OPERANDn_ALPHA
| Argument Value |
---|---|---|
GL_TEXTURE
|
GL_SRC_ALPHA
|
|
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_TEXTUREn
|
GL_SRC_ALPHA
|
|
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_CONSTANT
|
GL_SRC_ALPHA
|
|
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_PRIMARY_COLOR
|
GL_SRC_ALPHA
|
|
GL_ONE_MINUS_SRC_ALPHA
|
| |
GL_PREVIOUS
|
GL_SRC_ALPHA
|
|
GL_ONE_MINUS_SRC_ALPHA
|
|
The RGB and alpha results of the texture function are multipled by the
values of GL_RGB_SCALE
and GL_ALPHA_SCALE
, respectively, and
clamped to the range
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.
If pname
is GL_TEXTURE_LOD_BIAS
, the value specified is added to the
texture level-of-detail parameter, that selects which mipmap, or mipmaps
depending upon the selected GL_TEXTURE_MIN_FILTER
, will be sampled.
GL_TEXTURE_ENV_MODE
defaults to GL_MODULATE
and
GL_TEXTURE_ENV_COLOR
defaults to (0, 0, 0, 0).
If target
is GL_POINT_SPRITE
and pname
is GL_COORD_REPLACE
, the boolean value specified
is used to either enable or disable point sprite texture coordinate replacement. The default value is GL_FALSE
.
GL_REPLACE
may only be used if the GL version is 1.1 or greater.
GL_TEXTURE_FILTER_CONTROL
and GL_TEXTURE_LOD_BIAS
may only be
used if the GL version is 1.4 or greater.
GL_COMBINE
mode and its associated constants may only be used if the
GL version is 1.3 or greater.
GL_TEXTUREn
may only be used if the GL version is 1.4 or greater.
Internal formats other than 1, 2, 3, or 4 may only be used if the GL version is 1.1 or greater.
For OpenGL versions 1.3 and greater, or when the ARB_multitexture
extension is supported, glTexEnv
controls
the texture environment for the current active texture unit, selected by
glActiveTexture.
GL_POINT_SPRITE
and GL_COORD_REPLACE
are available
only if the GL version is 2.0 or greater.
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_VALUE
is generated if the params
value for
GL_RGB_SCALE
or GL_ALPHA_SCALE
are not one of 1.0, 2.0,
or 4.0.
GL_INVALID_OPERATION
is generated if glTexEnv
is executed between the execution of glBegin
and the corresponding execution of glEnd.
glActiveTexture, glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D, glTexImage1D, glTexImage2D, glTexImage3D, glTexParameter, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.