glTexParameter
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 )
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 parame-
ter. 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 ele-
ment. 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×2m, there are max(n,m)+1 mipmaps. The
first mipmap is the original texture, with dimensions 2n×2m.
Each subsequent mipmap has dimensions 2k−1×2l−1, where 2k×2l
are the dimensions of the previous mipmap, until either k=0
or l=0. At that point, subsequent mipmaps have dimension
1×2l−1 or 2k−1×1 until the final mipmap, which has dimension
1×1. 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 max(n,m) is the final 1×1 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 cen-
ter 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 cen-
ter 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 [__,1−__], 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.
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 discus-
sion 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 discus-
sion 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 com-
prise the RGBA color of the texture border. Integer color
components are interpreted linearly such that the most posi-
tive 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 informa-
tion.
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 dif-
fering 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, speci-
fied 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 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)
GLTEXPARAMETER(3G)
