GLTEXPARAMETER(3G)GLTEXPARAMETER(3G)NAME
glTexParameterf, glTexParameteri, glTexParameterfv, glTexParameteriv -
set texture parameters
C SPECIFICATION
void glTexParameterf( GLenum target,
GLenum pname,
GLfloat param )
void glTexParameteri( GLenum target,
GLenum pname,
GLint param )
delim $$
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 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, 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.
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 $2 sup n ~times~ 2 sup m$, there are $ bold max (
n, m ) + 1 $ mipmaps. The first mipmap is the original
texture, with dimensions $2 sup n ~times~ 2 sup m$. Each
subsequent mipmap has dimensions $2 sup { k - 1 } ~times~ 2
sup { l - 1 }$, where $2 sup k ~times~ 2 sup l$ are the
dimensions of the previous mipmap, until either $k ~=~ 0$ or
$l~=~0$. At that point, subsequent mipmaps have dimension $
1 ~times~ 2 sup { l - 1 } $ or $ 2 sup { k - 1} ~times~ 1 $
until the final mipmap, which has dimension $1 ~times~ 1$.
To define the mipmaps, call glTexImage1D, glTexImage2D,
glTexImage3D, glCopyTexImage1D, or glCopyTexImage2D with the
level argument indicating the order of the mipmaps. Level 0
is the original texture; level $ bold max ( n, m ) $ is the
final $1 ~times~ 1$ mipmap.
params supplies a function for minifying the texture 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 textured.
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 elements, 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 textured and uses the
GL_NEAREST criterion (the texture element nearest
to the center of the pixel) to produce a texture
value.
GL_LINEAR_MIPMAP_NEAREST
Chooses the mipmap that most closely matches 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.
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 average 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
average of those two values.
As more texture elements are sampled in the minification
process, fewer aliasing artifacts will be apparent. While the
GL_NEAREST and GL_LINEAR minification functions can be faster
than the other four, they sample only one or four texture
elements to determine the texture value of the pixel being
rendered and can produce moire patterns or 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 texture 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 textured.
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 elements, 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.
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
single image onto an object. GL_CLAMP_TO_EDGE causes $s$
coordinates to be clamped to the range $left [ {1 over 2N}, 1
- {1 over 2N} right ]$, 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 elements 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.
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 dimensions 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 executed between
the execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGetTexParameter
glGetTexLevelParameter
SEE ALSOglActiveTextureARB(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)
March 1, 2011
