Интерактивная система просмотра системных руководств (man-ов)
glTexParameter (3)
>> glTexParameter (3) ( Разные man: Библиотечные вызовы )
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 )
delim $$
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.
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 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 $2 sup n ~times~ 2 sup m$, there are
$ bold max ( n, m ) + 1 $ mipmaps.
The first mipmap is the original texture,
with dimensions $2 sup n ~times~ 2 sup m$.
Each subsequent mipmap has dimensions $2 sup { k - 1 } ~times~ 2 sup { l - 1 }$,
where $2 sup k ~times~ 2 sup l$ are the dimensions of the previous mipmap,
until either $k ~=~ 0$ or $l~=~0$.
At that point,
subsequent mipmaps have dimension $ 1 ~times~ 2 sup { l - 1 } $
or $ 2 sup { k - 1} ~times~ 1 $ until the final mipmap,
which has dimension $1 ~times~ 1$.
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 $ bold max ( n, m ) $ is the final $1 ~times~ 1$ 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
$left [ {1 over 2N}, 1 - {1 over 2N} right ]$, 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.
