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glTexParameter(3G)
NAME
glTexParameter - set texture parameters
SYNOPSIS
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^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 dimension 1 x 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 x 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 [ {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
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.
SYNOPSIS
void glTexParameterf(
(GLenum target,,
GLfloat param,,
GLenum pname) );
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 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.
ASSOCIATED GETS
glGetTexParameter glGetTexLevelParameter
SEE ALSO
glActiveTextureARB(3), glBindTexture(3), glCopyPixels(3),
glCopyTexImage1D(3), glCopyTexImage2D(3), glCopyTexSubImage1D(3),
glCopyTexSubImage2D(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),
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Index for
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Alphabetical
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