glTexParameter(3G)glTexParameter(3G)NAMEglTexParameter - set texture parameters
SYNOPSIS
void glTexParameterfv( GLenum target, GLenum pname, const GLfloat
*params ) void glTexParameteriv( GLenum target, GLenum pname,
const GLint *params )
PARAMETERS
Specifies the target texture, which must be either GL_TEXTURE_1D,
GL_TEXTURE_2D or GL_TEXTURE_3D. Specifies the symbolic name of a tex‐
ture parameter. pname can be one of the following: GL_TEXTURE_MIN_FIL‐
TER, 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_TEX‐
TURE_WRAP_T, GL_TEXTURE_WRAP_R, GL_TEXTURE_BORDER_COLOR, or GL_TEX‐
TURE_PRIORITY. Specifies a pointer to an array where the value or val‐
ues 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: The texture minifying function is used
whenever the pixel being textured maps to an area greater than one tex‐
ture 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 dimen‐
sions 2^n x 2^m, there are ( n, m ) + 1 mipmaps. The first
mipmap is the original texture, with dimensions 2^n X 2^m. Each
subsequent mipmap has dimensions 2^k - 1 x 2^l - 1, where 2^k x
2^l are the dimensions of the previous mipmap, until either k =
0 or l = 0. At that point, subsequent mipmaps have dimension 1 x
2^l - 1 or 2^k - 1 x 1 until the final mipmap, which has dimen‐
sion 1 x 1. To define the mipmaps, call glTexImage1D, glTexIm‐
age2D, glTexImage3D, glCopyTexImage1D, or glCopyTexImage2D with
the level argument indicating the order of the mipmaps. Level 0
is the original texture; level max( n, m ) is the final 1 x 1
mipmap.
params supplies a function for minifying the texture as one of
the following: Returns the value of the texture element that is
nearest (in Manhattan distance) to the center of the pixel being
textured. Returns the weighted average of the four texture ele‐
ments that are closest to the center of the pixel being tex‐
tured. 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. 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. 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. Chooses the two mipmaps that most closely
match the size of the pixel being textured and uses the GL_NEAR‐
EST 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.
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 ele‐
ments to determine the texture value of the pixel being rendered
and can produce moire patterns or ragged transitions. The ini‐
tial value of GL_TEXTURE_MIN_FILTER is GL_NEAREST_MIPMAP_LINEAR.
The texture magnification function is used when the pixel being
textured maps to an area less than or equal to one texture ele‐
ment. 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. Returns the value of the texture element that is
nearest (in Manhattan distance) to the center of the pixel being
textured. Returns the weighted average of the four texture ele‐
ments that are closest to the center of the pixel being tex‐
tured. 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.
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.
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.
Specifies the index of the lowest defined mipmap level. This is an
integer value. The initial value is 0.
Sets the index of the highest defined mipmap level. This is an integer
value. The initial value is 1000.
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 arti‐
facts when mapping a single image onto an object. GL_CLAMP_TO_EDGE
causes s coordinates to be clamped to the range [ {1 over 2N}, 1 - {1
over 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 elements are accessed only if wrap‐
ping is set to GL_CLAMP. Initially, GL_TEXTURE_WRAP_S is set to
GL_REPEAT.
Sets the wrap parameter for texture coordinate t to either GL_CLAMP,
GL_CLAMP_TO_EDGE, or GL_REPEAT. See the discussion under GL_TEX‐
TURE_WRAP_S. Initially, GL_TEXTURE_WRAP_T is set to GL_REPEAT. Sets
the wrap parameter for texture coordinate r to either GL_CLAMP,
GL_CLAMP_TO_EDGE, or GL_REPEAT. See the discussion under GL_TEX‐
TURE_WRAP_S. Initially, GL_TEXTURE_WRAP_R is set to GL_REPEAT. Sets a
border color. params contains four values that comprise the RGBA color
of the texture border. Integer color components are interpreted lin‐
early 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). Specifies the texture residence priority of the currently bound
texture. Permissible values are in the range [0, 1]. See glPrioritize‐
Textures and glBindTexture for more information.
NOTES
GL_TEXTURE_3D, GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD, GL_TEX‐
TURE_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, glCopyTex‐
Image1D, 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.
SYNOPSIS
void glTexParameterf(
(GLenum target,,
GLfloat param,,
GLenum pname) ); void glTexParameteri(
(GLenum target,,
GLenum pname,,
GLint param) );
PARAMETERS
Specifies the target texture, which must be either GL_TEXTURE_1D,
GL_TEXTURE_2D, or GL_TEXTURE_3D. Specifies the symbolic name of a sin‐
gle-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_TEX‐
TURE_PRIORITY. Specifies the value of pname.
ASSOCIATED GETS
glGetTexParameter glGetTexLevelParameter
SEE ALSOglActiveTextureARB(3), glBindTexture(3), glCopyPixels(3), glCopyTexIm‐
age1D(3), glCopyTexImage2D(3), glCopyTexSubImage1D(3), glCopyTexSubIm‐
age2D(3), glCopyTexSubImage3D(3), glDrawPixels(3), glPixelStore(3),
glPixelTransfer(3), glPrioritizeTextures(3), glTexEnv(3), glTexGen(3),
glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glTexSubImage1D(3),
(3), glTexSubImage2D(3glTexSubImage3D),
glTexParameter(3G)