GLTEXPARAMETER(3G) UNIX Programmer's Manual GLTEXPARAMETER(3G)
NAME
glTexParameterf, glTexParameteri, glTexParameterfv, glTex-
Parameteriv - set texture parameters
C SPECIFICATION
void glTexParameterf( GLenum target,
GLenum pname,
GLfloat param )
void glTexParameteri( GLenum target,
GLenum pname,
GLint param )
PARAMETERS
target Specifies the target texture, which must be either
GL_TEXTURE_1D, GL_TEXTURE_2D, or GL_TEXTURE_3D.
pname Specifies the symbolic name of a single-valued tex-
ture parameter. pname can be one of the following:
GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER,
GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD,
GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL,
GL_TEXTURE_WRAP_S, GL_TEXTURE_WRAP_T,
GL_TEXTURE_WRAP_R, or GL_TEXTURE_PRIORITY.
param Specifies the value of pname.
C SPECIFICATION
void glTexParameterfv( GLenum target,
GLenum pname,
const GLfloat *params )
void glTexParameteriv( GLenum target,
GLenum pname,
const GLint *params )
PARAMETERS
target
Specifies the target texture, which must be either
GL_TEXTURE_1D, GL_TEXTURE_2D or GL_TEXTURE_3D.
pname
Specifies the symbolic name of a texture parameter.
pname can be one of the following:
GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER,
GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD,
GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL,
GL_TEXTURE_WRAP_S, GL_TEXTURE_WRAP_T,
GL_TEXTURE_WRAP_R, GL_TEXTURE_BORDER_COLOR, or
GL_TEXTURE_PRIORITY.
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params
Specifies a pointer to an array where the value or
values of pname are stored.
DESCRIPTION
Texture mapping is a technique that applies an image onto an
object's surface as if the image were a decal or cellophane
shrink-wrap. The image is created in texture space, with an
(s, t) coordinate system. A texture is a one- or two-
dimensional image and a set of parameters that determine how
samples are derived from the image.
glTexParameter assigns the value or values in params to the
texture parameter specified as pname. target defines the
target texture, either GL_TEXTURE_1D, GL_TEXTURE_2D, or
GL_TEXTURE_3D. The following symbols are accepted in pname:
GL_TEXTURE_MIN_FILTER
The texture minifying function is used whenever
the pixel being textured maps to an area greater
than one texture element. There are six defined
minifying functions. Two of them use the nearest
one or nearest four texture elements to compute
the texture value. The other four use mipmaps.
A mipmap is an ordered set of arrays representing
the same image at progressively lower resolutions.
If the texture has dimensions 2n x 2m, there are
max(n,m)+1 mipmaps. The first mipmap is the origi-
nal texture, with dimensions 2n x 2m. Each subse-
quent mipmap has dimensions 2k-1 x 2l-1, where
2k x 2l are the dimensions of the previous mipmap,
until either k = 0 or l = 0. At that point, subse-
quent mipmaps have dimension 1 x 2l-1 or 2k-1 x 1
until the final mipmap, which has dimension 1 x 1.
To define the mipmaps, call glTexImage1D,
glTexImage2D, glTexImage3D, glCopyTexImage1D, or
glCopyTexImage2D with the level argument indicat-
ing the order of the mipmaps. Level 0 is the ori-
ginal texture; level max(n,m) is the final 1 x 1
mipmap.
params supplies a function for minifying the tex-
ture as one of the following:
GL_NEAREST
Returns the value of the texture element
that is nearest (in Manhattan distance)
to the center of the pixel being tex-
tured.
GL_LINEAR Returns the weighted average of the four
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texture elements that are closest to the
center of the pixel being textured.
These can include border texture ele-
ments, depending on the values of
GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T,
and on the exact mapping.
GL_NEAREST_MIPMAP_NEAREST
Chooses the mipmap that most closely
matches the size of the pixel being tex-
tured and uses the GL_NEAREST criterion
(the texture element nearest to the
center of the pixel) to produce a tex-
ture value.
GL_LINEAR_MIPMAP_NEAREST
Chooses the mipmap that most closely
matches the size of the pixel being tex-
tured and uses the GL_LINEAR criterion
(a weighted average of the four texture
elements that are closest to the center
of the pixel) to produce a texture
value.
GL_NEAREST_MIPMAP_LINEAR
Chooses the two mipmaps that most
closely match the size of the pixel
being textured and uses the GL_NEAREST
criterion (the texture element nearest
to the center of the pixel) to produce a
texture value from each mipmap. The
final texture value is a weighted aver-
age of those two values.
GL_LINEAR_MIPMAP_LINEAR
Chooses the two mipmaps that most
closely match the size of the pixel
being textured and uses the GL_LINEAR
criterion (a weighted average of the
four texture elements that are closest
to the center of the pixel) to produce a
texture value from each mipmap. The
final texture value is a weighted aver-
age of those two values.
As more texture elements are sampled in the minif-
ication process, fewer aliasing artifacts will be
apparent. While the GL_NEAREST and GL_LINEAR min-
ification functions can be faster than the other
four, they sample only one or four texture ele-
ments to determine the texture value of the pixel
being rendered and can produce moire patterns or
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ragged transitions. The initial value of
GL_TEXTURE_MIN_FILTER is GL_NEAREST_MIPMAP_LINEAR.
GL_TEXTURE_MAG_FILTER
The texture magnification function is used when
the pixel being textured maps to an area less than
or equal to one texture element. It sets the tex-
ture magnification function to either GL_NEAREST
or GL_LINEAR (see below). GL_NEAREST is generally
faster than GL_LINEAR, but it can produce textured
images with sharper edges because the transition
between texture elements is not as smooth. The
initial value of GL_TEXTURE_MAG_FILTER is
GL_LINEAR.
GL_NEAREST
Returns the value of the texture element
that is nearest (in Manhattan distance)
to the center of the pixel being tex-
tured.
GL_LINEAR Returns the weighted average of the four
texture elements that are closest to the
center of the pixel being textured.
These can include border texture ele-
ments, depending on the values of
GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T,
and on the exact mapping.
GL_TEXTURE_MIN_LOD
Sets the minimum level-of-detail parameter. This
floating-point value limits the selection of
highest resolution mipmap (lowest mipmap level).
The initial value is -1000.
GL_TEXTURE_MAX_LOD
Sets the maximum level-of-detail parameter. This
floating-point value limits the selection of the
lowest resolution mipmap (highest mipmap level).
The initial value is 1000.
GL_TEXTURE_BASE_LEVEL
Specifies the index of the lowest defined mipmap
level. This is an integer value. The initial value
is 0.
GL_TEXTURE_MAX_LEVEL
Sets the index of the highest defined mipmap
level. This is an integer value. The initial value
is 1000.
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GL_TEXTURE_WRAP_S
Sets the wrap parameter for texture coordinate s
to either GL_CLAMP, GL_CLAMP_TO_EDGE, or
GL_REPEAT. GL_CLAMP causes s coordinates to be
clamped to the range [0,1] and is useful for
preventing wrapping artifacts when mapping a sin-
gle image onto an object. GL_CLAMP_TO_EDGE causes
s coor_i_|ates to be clamped to the range
|__,1-2N|, where N is the size of the texture in
the direction of clamping. GL_REPEAT causes the
integer part of the s coordinate to be ignored;
the GL uses only the fractional part, thereby
creating a repeating pattern. Border texture ele-
ments are accessed only if wrapping is set to
GL_CLAMP. Initially, GL_TEXTURE_WRAP_S is set to
GL_REPEAT.
GL_TEXTURE_WRAP_T
Sets the wrap parameter for texture coordinate t
to either GL_CLAMP, GL_CLAMP_TO_EDGE, or
GL_REPEAT. See the discussion under
GL_TEXTURE_WRAP_S. Initially, GL_TEXTURE_WRAP_T is
set to GL_REPEAT.
GL_TEXTURE_WRAP_R
Sets the wrap parameter for texture coordinate r
to either GL_CLAMP, GL_CLAMP_TO_EDGE, or
GL_REPEAT. See the discussion under
GL_TEXTURE_WRAP_S. Initially, GL_TEXTURE_WRAP_R is
set to GL_REPEAT.
GL_TEXTURE_BORDER_COLOR
Sets a border color. params contains four values
that comprise the RGBA color of the texture
border. 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. Initially, the border
color is (0, 0, 0, 0).
GL_TEXTURE_PRIORITY
Specifies the texture residence priority of the
currently bound texture. Permissible values are in
the range [0, 1]. See glPrioritizeTextures and
glBindTexture for more information.
NOTES
GL_TEXTURE_3D, GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD,
GL_TEXTURE_BASE_LEVEL, and GL_TEXTURE_MAX_LEVEL are only
available if the GL version is 1.2 or greater.
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Suppose that a program has enabled texturing (by calling
glEnable with argument GL_TEXTURE_1D, GL_TEXTURE_2D, or
GL_TEXTURE_3D) and has set GL_TEXTURE_MIN_FILTER to one of
the functions that requires a mipmap. If either the dimen-
sions of the texture images currently defined (with previous
calls to glTexImage1D, glTexImage2D, glTexImage3D,
glCopyTexImage1D, or glCopyTexImage2D) do not follow the
proper sequence for mipmaps (described above), or there are
fewer texture images defined than are needed, or the set of
texture images have differing numbers of texture components,
then it is as if texture mapping were disabled.
Linear filtering accesses the four nearest texture elements
only in 2D textures. In 1D textures, linear filtering
accesses the two nearest texture elements.
When the GL_ARB_multitexture extension is supported,
glTexParameter specifies the texture parameters for the
active texture unit, specified by calling
glActiveTextureARB.
ERRORS
GL_INVALID_ENUM is generated if target or pname is not one
of the accepted defined values.
GL_INVALID_ENUM is generated if params should have a defined
constant value (based on the value of pname) and does not.
GL_INVALID_OPERATION is generated if glTexParameter is exe-
cuted between the execution of glBegin and the corresponding
execution of glEnd.
ASSOCIATED GETS
glGetTexParameter
glGetTexLevelParameter
SEE ALSO
glActiveTextureARB(3G), glBindTexture(3G), glCopyPixels(3G),
glCopyTexImage1D(3G), glCopyTexImage2D(3G),
glCopyTexSubImage1D(3G), glCopyTexSubImage2D(3G),
glCopyTexSubImage3D(3G), glDrawPixels(3G), glPixelStore(3G),
glPixelTransfer(3G), glPrioritizeTextures(3G), glTexEnv(3G),
glTexGen(3G), glTexImage1D(3G), glTexImage2D(3G),
glTexImage3D(3G), glTexSubImage1D(3G), glTexSubImage2D(3G),
glTexSubImage3D(3G)
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