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 or GL_TEXTURE_2D.
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_WRAP_S,
GL_TEXTURE_WRAP_T, 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 or GL_TEXTURE_2D.
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_WRAP_S, GL_TEXTURE_WRAP_T,
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 or GL_TEXTURE_2D. 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 2nx2m, there are
max(n,m)+1 mipmaps. The first mipmap is the
original texture, with dimensions 2nx2m. Each
subsequent mipmap has dimensions 2k-1x2l-1, where
2kx2l are the dimensions of the previous mipmap,
until either k=0 or l=0. At that point,
subsequent mipmaps have dimension 1x2l-1 or 2k-1x1
until the final mipmap, which has dimension 1x1.
To define the mipmaps, call glTexImage1D,
glTexImage2D, 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:
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_WRAP_S
Sets the wrap parameter for texture coordinate s
to either GL_CLAMP 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_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 or GL_REPEAT. See the
discussion under GL_TEXTURE_WRAP_S. Initially,
GL_TEXTURE_WRAP_T 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
Suppose that a program has enabled texturing (by calling
glEnable with argument GL_TEXTURE_1D or GL_TEXTURE_2D) 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, 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.
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
glBindTexture, glCopyPixels, glCopyTexImage1D,
glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D,
glDrawPixels, glPixelStore, glPixelTransfer,
glPrioritizeTextures, glTexEnv, glTexGen, glTexImage1D,
glTexImage2D, glTexSubImage1D, glTexSubImage2D