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
GLTEXTURE1D, GLTEXTURE2D, or GLTEXTURE3D.
pname Specifies the symbolic name of a single-valued texture parame-
ter. pname can be one of the following: GLTEXTUREMINFILTER,
GLTEXTUREMAGFILTER, GLTEXTUREMINLOD, GLTEXTUREMAXLOD,
GLTEXTUREBASELEVEL, GLTEXTUREMAXLEVEL, GLTEXTUREWRAPS,
GLTEXTUREWRAPT, GLTEXTUREWRAPR, or GLTEXTUREPRIORITY.
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
GLTEXTURE1D, GLTEXTURE2D or GLTEXTURE3D.
pname Specifies the symbolic name of a texture parameter. pname can
be one of the following: GLTEXTUREMINFILTER,
GLTEXTUREMAGFILTER, GLTEXTUREMINLOD, GLTEXTUREMAXLOD,
GLTEXTUREBASELEVEL, GLTEXTUREMAXLEVEL, GLTEXTUREWRAPS,
GLTEXTUREWRAPT, GLTEXTUREWRAPR, GLTEXTUREBORDERCOLOR,
or GLTEXTUREPRIORITY.
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 GLTEXTURE1D, GLTEXTURE2D, or GLTEXTURE3D. The following
symbols are accepted in pname:
GLTEXTUREMINFILTER
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 2^n x 2^m, there are max ( 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, subse-
quent mipmaps have dimension 1 x 2^(l-1) or 2^(k-1) x 1
until the final mipmap, which has dimension 1x1. 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 1x1 mipmap.
params supplies a function for minifying the texture as one
of the following:
GLNEAREST
Returns the value of the texture element that is
nearest (in Manhattan distance) to the center of
the pixel being textured.
GLINEAR 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
GLTEXTUREWRAPS and GLTEXTUREWRAPT, and on the
exact mapping.
GLNEARESTMIPMAPNEAREST
Chooses the mipmap that most closely matches the
size of the pixel being textured and uses the
GLNEAREST criterion (the texture element nearest
to the center of the pixel) to produce a texture
value.
GLINEARMIPMAPNEAREST
Chooses the mipmap that most closely matches the
size of the pixel being textured and uses the
GLINEAR criterion (a weighted average of the four
texture elements that are closest to the center of
the pixel) to produce a texture value.
GLNEARESTMIPMAPLINEAR
Chooses the two mipmaps that most closely match the
size of the pixel being textured and uses the
GLNEAREST 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.
GLINEARMIPMAPLINEAR
Chooses the two mipmaps that most closely match the
size of the pixel being textured and uses the
GLINEAR 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 GLNEAREST and GLINEAR minification functions can be
faster than the other four, they sample only one or four tex-
ture elements to determine the texture value of the pixel
being rendered and can produce moire patterns or ragged tran-
sitions. The initial value of GLTEXTUREMINFILTER is
GLNEARESTMIPMAPLINEAR.
GLTEXTUREMAGFILTER
The texture magnification function is used when the pixel
being textured maps to an area less than or equal to one tex-
ture element. It sets the texture magnification function to
either GLNEAREST or GLINEAR (see below). GLNEAREST is
generally faster than GLINEAR, but it can produce textured
images with sharper edges because the transition between tex-
ture elements is not as smooth. The initial value of
GLTEXTUREMAGFILTER is GLINEAR.
GLNEAREST
Returns the value of the texture element that is
nearest (in Manhattan distance) to the center of
the pixel being textured.
GLINEAR 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
GLTEXTUREWRAPS and GLTEXTUREWRAPT, and on the
exact mapping.
GLTEXTUREMINLOD
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.
GLTEXTUREMAXLOD
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.
GLTEXTUREBASELEVEL
Specifies the index of the lowest defined mipmap level. This
is an integer value. The initial value is 0.
GLTEXTUREMAXLEVEL
Sets the index of the highest defined mipmap level. This is
an integer value. The initial value is 1000.
GLTEXTUREWRAPS
Sets the wrap parameter for texture coordinate s to either
GLCLAMP, GLCLAMPTOEDGE, or GLREPEAT. GLCLAMP 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. GLCLAMPTOEDGE causes s coordinates to be
clamped to the range 1/2N, 1-1/2N, where N is the size of the
texture in the direction of clamping. GLREPEAT causes the
integer part of the s coordinate to be ignored; the GL uses
only the fractional part, thereby creating a repeating pat-
tern. Border texture elements are accessed only if wrapping
is set to GLCLAMP. Initially, GLTEXTUREWRAPS is set to
GLREPEAT.
GLTEXTUREWRAPT
Sets the wrap parameter for texture coordinate t to either
GLCLAMP, GLCLAMPTOEDGE, or GLREPEAT. See the discussion
under GLTEXTUREWRAPS. Initially, GLTEXTUREWRAPT is set
to GLREPEAT.
GLTEXTUREWRAPR
Sets the wrap parameter for texture coordinate r to either
GLCLAMP, GLCLAMPTOEDGE, or GLREPEAT. See the discussion
under GLTEXTUREWRAPS. Initially, GLTEXTUREWRAPR is set
to GLREPEAT.
GLTEXTUREBORDERCOLOR
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).
GLTEXTUREPRIORITY
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
GLTEXTURE3D, GLTEXTUREMINLOD, GLTEXTUREMAXLOD,
GLTEXTUREBASELEVEL, and GLTEXTUREMAXLEVEL are only available if
the GL version is 1.2 or greater.
Suppose that a program has enabled texturing (by calling glEnable with
argument GLTEXTURE1D, GLTEXTURE2D, or GLTEXTURE3D) and has set
GLTEXTUREMINFILTER 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 GLARBmultitexture extension is supported, glTexParameter
specifies the texture parameters for the active texture unit, specified
by calling glActiveTextureARB.
ERORS
GLINVALIDENUM is generated if target or pname is not one of the
accepted defined values.
GLINVALIDENUM is generated if params should have a defined constant
value (based on the value of pname) and does not.
GLINVALIDOPERATION is generated if glTexParameter is executed between
the execution of glBegin and the corresponding execution of glEnd.
ASOCIATED GETS
glGetTexParameter
glGetTexLevelParameter
SEE ALSO
glActiveTextureARB, glBindTexture, glCopyPixels, glCopyTexImage1D,
glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D,
glCopyTexSubImage3D, glDrawPixels, glPixelStore, glPixelTransfer,
glPrioritizeTextures, glTexEnv, glTexGen, glTexImage1D, glTexImage2D,
glTexImage3D, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D
GLTEXPARAMETER(3G)
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