glTexParameter — set texture parameters
void glTexParameterf( | GLenum | target, |
GLenum | pname, | |
GLfloat | param) ; |
void glTexParameteri( | GLenum | target, |
GLenum | pname, | |
GLint | param) ; |
target
Specifies the target texture,
which must be either GL_TEXTURE_1D
, GL_TEXTURE_2D
,
GL_TEXTURE_3D
, or GL_TEXTURE_CUBE_MAP
.
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
,
GL_TEXTURE_PRIORITY
,
GL_TEXTURE_COMPARE_MODE
,
GL_TEXTURE_COMPARE_FUNC
,
GL_DEPTH_TEXTURE_MODE
, or
GL_GENERATE_MIPMAP
.
param
Specifies the value of pname
.
void glTexParameterfv( | GLenum | target, |
GLenum | pname, | |
const GLfloat * | params) ; |
void glTexParameteriv( | GLenum | target, |
GLenum | pname, | |
const GLint * | params) ; |
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
,
GL_TEXTURE_PRIORITY
,
GL_TEXTURE_COMPARE_MODE
,
GL_TEXTURE_COMPARE_FUNC
,
GL_DEPTH_TEXTURE_MODE
, or
GL_GENERATE_MIPMAP
.
params
Specifies a pointer to an array where the value or values of pname
are stored.
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
(
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
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
GL_CLAMP
,
GL_CLAMP_TO_BORDER
, GL_CLAMP_TO_EDGE
, GL_MIRRORED_REPEAT
, or
GL_REPEAT
. GL_CLAMP
causes
GL_CLAMP_TO_BORDER
causes the
GL_CLAMP_TO_EDGE
causes
GL_REPEAT
causes the
integer part of the
GL_MIRRORED_REPEAT
causes the
GL_CLAMP
or GL_CLAMP_TO_BORDER
. Initially,
GL_TEXTURE_WRAP_S
is set to GL_REPEAT
.
GL_TEXTURE_WRAP_T
Sets the wrap parameter for texture coordinate
GL_CLAMP
,
GL_CLAMP_TO_BORDER
, GL_CLAMP_TO_EDGE
, GL_MIRRORED_REPEAT
, 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
GL_CLAMP
,
GL_CLAMP_TO_BORDER
, GL_CLAMP_TO_EDGE
, GL_MIRRORED_REPEAT
, 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
GL_TEXTURE_COMPARE_MODE
Specifies the texture comparison mode for currently bound depth textures.
That is, a texture whose internal format is GL_DEPTH_COMPONENT_*
; see
glTexImage2D)
Permissible values are:
GL_COMPARE_R_TO_TEXTURE
Specifies that the interpolated and clamped
GL_TEXTURE_COMPARE_FUNC
for details of how the comparison
is evaluated. The result of the comparison is assigned to luminance,
intensity, or alpha (as specified by GL_DEPTH_TEXTURE_MODE
).
GL_NONE
Specifies that the luminance, intensity, or alpha (as specified by
GL_DEPTH_TEXTURE_MODE
) should be assigned the
appropriate value from the currently bound depth texture.
GL_TEXTURE_COMPARE_FUNC
Specifies the comparison operator used when GL_TEXTURE_COMPARE_MODE
is
set to GL_COMPARE_R_TO_TEXTURE
. Permissible values are:
Texture Comparison Function | Computed result |
---|---|
GL_LEQUAL
|
|
GL_GEQUAL
|
|
GL_LESS
|
|
GL_GREATER
|
|
GL_EQUAL
|
|
GL_NOTEQUAL
|
|
GL_ALWAYS
|
|
GL_NEVER
|
|
where GL_DEPTH_TEXTURE_MODE
.)
GL_DEPTH_TEXTURE_MODE
Specifies a single symbolic constant indicating how depth values should be
treated during filtering and texture application. Accepted values are
GL_LUMINANCE
, GL_INTENSITY
, and GL_ALPHA
. The initial value
is GL_LUMINANCE
.
GL_GENERATE_MIPMAP
Specifies a boolean value that indicates if all levels of a mipmap array
should be automatically updated when any modification to the base level
mipmap is done. The initial value is GL_FALSE
.
GL_TEXTURE_3D
, GL_TEXTURE_MIN_LOD
, GL_TEXTURE_MAX_LOD
,
GL_CLAMP_TO_EDGE
, GL_TEXTURE_BASE_LEVEL
, and GL_TEXTURE_MAX_LEVEL
are
available only if the GL version is 1.2 or greater.
GL_CLAMP_TO_BORDER
is available only if the GL version is 1.3 or greater.
GL_MIRRORED_REPEAT
, GL_TEXTURE_COMPARE_MODE
,
GL_TEXTURE_COMPARE_FUNC
, GL_DEPTH_TEXTURE_MODE
, and
GL_GENERATE_MIPMAP
are available only if the GL version is 1.4 or
greater.
GL_TEXTURE_COMPARE_FUNC
allows the following additional comparison modes only
if the GL version is 1.5 or greater:
GL_LESS
, GL_GREATER
,
GL_EQUAL
, GL_NOTEQUAL
,
GL_ALWAYS
, and GL_NEVER
.
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.
For OpenGL versions 1.3 and greater, or when the ARB_multitexture
extension is supported, glTexParameter
specifies the texture parameters for the active texture unit, specified
by calling glActiveTexture.
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.
glActiveTexture, glBindTexture, glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D, glDrawPixels, glPixelStore, glPixelTransfer, glPrioritizeTextures, glTexEnv, glTexGen, glTexImage1D, glTexImage2D, glTexImage3D, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.