glTexParameter(3G) OpenGL Reference glTexParameter(3G)
glTexParameterf, glTexParameteri, glTexParameterfv, glTexParameteriv -
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_DETAIL_TEXTURE_2D_SGIS, or GL_TEXTURE_3D_EXT.
GL_TEXTURE_4D_SGIS.
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_WRAP_Q_SGIS,
GL_TEXTURE_PRIORITY, GL_DETAIL_TEXTURE_LEVEL_SGIS,
GL_DETAIL_TEXTURE_MODE_SGIS, GL_TEXTURE_BASE_LEVEL_SGIS,
GL_TEXTURE_MAX_LEVEL_SGIS, GL_TEXTURE_MIN_LOD_SGIS,
GL_TEXTURE_MAX_LOD_SGIS, GL_TEXTURE_LOD_BIAS_S_SGIX,
GL_TEXTURE_LOD_BIAS_T_SGIX, GL_TEXTURE_LOD_BIAS_R_SGIX,
GL_TEXTURE_MAX_CLAMP_S_SGIX, GL_TEXTURE_MAX_CLAMP_T_SGIX,
GL_TEXTURE_MAX_CLAMP_R_SGIX, GL_DUAL_TEXTURE_SELECT_SGIS,
GL_QUAD_TEXTURE_SELECT_SGIS, GL_TEXTURE_CLIPMAP_FRAME_SGIX,
GL_TEXTURE_COMPARE_SGIX, GL_TEXTURE_COMPARE_OPERATOR_SGIX, or
GL_SHADOW_AMBIENT_SGIX.
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, GL_DETAIL_TEXTURE_2D_SGIS, or GL_TEXTURE_3D_EXT.
GL_TEXTURE_4D_SGIS.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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_WRAP_Q_SGIS, GL_TEXTURE_PRIORITY,
GL_DETAIL_TEXTURE_LEVEL_SGIS, GL_DETAIL_TEXTURE_MODE_SGIS,
GL_POST_TEXTURE_FILTER_BIAS_SGIX, GL_POST_TEXTURE_FILTER_SCALE_SGIX,
GL_TEXTURE_BORDER_COLOR, GL_TEXTURE_BASE_LEVEL_SGIS,
GL_TEXTURE_MAX_LEVEL_SGIS, GL_TEXTURE_MIN_LOD_SGIS,
GL_TEXTURE_MAX_LOD_SGIS, GL_TEXTURE_LOD_BIAS_S_SGIX,
GL_TEXTURE_LOD_BIAS_T_SGIX, GL_TEXTURE_LOD_BIAS_R_SGIX,
GL_TEXTURE_MAX_CLAMP_S_SGIX, GL_TEXTURE_MAX_CLAMP_T_SGIX,
GL_TEXTURE_MAX_CLAMP_R_SGIX, GL_DUAL_TEXTURE_SELECT_SGIS,
GL_QUAD_TEXTURE_SELECT_SGIS, GL_TEXTURE_CLIPMAP_FRAME_SGIX,
GL_TEXTURE_CLIPMAP_CENTER_SGIX, GL_TEXTURE_CLIPMAP_OFFSET_SGIX,
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX, GL_TEXTURE_COMPARE_SGIX,
GL_TEXTURE_COMPARE_OPERATOR_SGIX, or GL_SHADOW_AMBIENT_SGIX.
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 (s, t, r) coordinate system. A
texture is a one-, two-, or three-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, GL_DETAIL_TEXTURE_2D_SGIS, GL_TEXTURE_3D,
or GL_TEXTURE_4D_SGIS. The following symbols are accepted in pname:
GL_TEXTURE_MIN_FILTER [Toc] [Back]
The texture minifying function is used whenever the pixel being
textured maps to an area greater than one texture element.
There are eight defined minifying functions. Two of them use
the nearest one or nearest four texture elements to compute the
texture value. Four use mipmaps, and one uses a mipmap variant
called a clipmap. One uses an application-specified filter
that combines four adjacent texture elements (in the 1D case)
or sixteen adjacent texture elements (in the 2D case).
A mipmap is an ordered set of arrays representing the same
image at progressively lower resolutions. If the texture has
n m
dimensions 2 x 2 , there are max(n,m)+1 mipmaps. The first
n m
mipmap is the original texture, with dimensions 2 x 2 . Each
k-1 l-1 k l
subsequent mipmap has dimensions 2 x 2 , where 2 x 2 are
the dimensions of the previous mipmap, until either k = 0 or
l = 0. At that point, subsequent mipmaps have dimension
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
l-1 k-1
1 x 2 or 2 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.
A clipmap virtualizes a 2D mipmap by storing and using only a
portion of a full mipmap ``pyramid'' at any given time. In a
clipmap with N+1 levels numbered 0 (the base) through N (the
tip), each image level from B through N contains the full image
from the corresponding level of the complete mipmap. Each
image level from 0 through B-1 contains a subimage of the
corresponding level of the complete mipmap, called the region
of interest. The region of interest must be the same size in
all the levels 0 through B-1 - that is, precisely the same size
as the texture image at mipmap level B. For the clipmap to be
usable, only the region of interest need reside in texture
memory. When texture filtering requires texels (texture
elements) that are inside the region of interest for a level,
they are fetched in just the way they would be accessed for a
mipmap. When the required texels fall outside the region of
interest, then successively higher clipmap levels are queried
until one is found that contains texels at the appropriate
coordinates.
Since each 2D mipmap level usually contains four times as many
texels as the subsequent level, using a clipmap for a few of
the highest-resolution levels can reduce texture memory
requirements tremendously. In addition to reducing memory
requirements, clipmaps also have features that support paging
texture images into and out of texture memory. Clipmaps also
can be virtualized to support many more levels of detail than
ordinarily would be available. (See below for more information
on paging and virtualization.) Note that clipmaps may be used
only with borderless 2D textures.
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 two, four, or
eight 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, GL_TEXTURE_WRAP_T, and
GL_TEXTURE_WRAP_R, and on the exact mapping.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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.
GL_PIXEL_TEX_GEN_Q_CEILING_SGIX
GL_PIXEL_TEX_GEN_Q_FLOOR_SGIX
GL_PIXEL_TEX_GEN_Q_ROUND_SGIX
The SGIX_impact_pixel_texture extension allows the
glPixelTexGenSGIX command to utilize a 4D texture
when there is no hardware support for linear
interpolation in the q coordinate. In this case the
application may get the desired result from a twopass
operation; on the first pass the filter function
is set to ceiling with alpha-blending disabled,
followed by a second pass set to floor with the
appropriate blendfunction set. If a nearest-neighbor
mode is acceptable, a one-pass method can be used
with the filter set to round (the default).
Additional information about 4D pixel-texturing can
be found man pages for glPixelTexGenSGIX.
Page 4
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_FILTER4_SGIS
Returns a weighted average of the four texture
elements (in the 1D case) or the sixteen texture
elements (in the 2D case) that are closest to the
center of the pixel being textured. These can
include border texture elements, although the
behavior in such cases is rarely useful. The weights
are derived from a filter kernel specified by the
user; see glTexFilterFuncSGIS for details. Note that
this mode is not supported for 3D textures.
GL_LINEAR_CLIPMAP_LINEAR_SGIX
Similar to GL_LINEAR_MIPMAP_LINEAR, but used only
with clipmaps. This method may be used with any
magnification filter except GL_FILTER4_SGIS; however,
detail and sharpen filtering are performed only when
texels are supplied by the level 0 image of the
clipmap.
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 four mipmap filtering modes, they sample only one,
four, or eight 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 [Toc] [Back]
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 any of
the following. 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 two, four, or
eight 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, GL_TEXTURE_WRAP_T, and
GL_TEXTURE_WRAP_R, and on the exact mapping.
GL_LINEAR_DETAIL_SGIS
Returns a weighted average of samples from the
current 2D texture and from the current 2D detail
Page 5
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
texture, for all four color components.
GL_LINEAR_DETAIL_ALPHA_SGIS
Returns a weighted average of samples from the
current 2D texture and from the current 2D detail
texture for the alpha color component; the other
three color components are returned as for GL_LINEAR.
GL_LINEAR_DETAIL_COLOR_SGIS
Returns a weighted average of samples from the
current 2D texture and from the current 2D detail
texture for the red, green, and blue color
components; the alpha color component is returned as
for GL_LINEAR.
GL_LINEAR_SHARPEN_SGIS
Returns an extrapolation derived from level zero and
level one texture image samples. This is similar to
GL_LINEAR filtering, but with less blurring.
GL_LINEAR_SHARPEN_ALPHA_SGIS
Returns a sharpened extrapolated value for the alpha
color component. All other color components are
returned as for GL_LINEAR.
GL_LINEAR_SHARPEN_COLOR_SGIS
Returns sharpened extrapolated values for the red,
green, and blue color components. The alpha
component is returned as for GL_LINEAR.
GL_PIXEL_TEX_GEN_Q_CEILING_SGIX
GL_PIXEL_TEX_GEN_Q_FLOOR_SGIX
GL_PIXEL_TEX_GEN_Q_ROUND_SGIX
The SGIX_impact_pixel_texture extension allows the
glPixelTexGenSGIX command to utilize a 4D texture
when there is no hardware support for linear
interpolation in the q coordinate. In this case the
application may get the desired result from a twopass
operation; on the first pass the filter function
is set to ceiling with alpha-blending disabled,
followed by a second pass set to floor with the
appropriate blendfunction set. If a nearest-neighbor
mode is acceptable, a one-pass method can be used
with the filter set to round (the default).
Additional information about 4D pixel-texturing can
be found man pages for glPixelTexGenSGIX.
Page 6
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_FILTER4_SGIS
As with minification, returns a weighted average of
the four texture elements (in the 1D case) or the
sixteen texture elements (in the 2D case) that are
closest to the center of the pixel being textured.
These can include border texture elements, although
the behavior in such cases is rarely useful. The
weights are derived from a filter kernel specified by
the user; see glTexFilterFuncSGIS. Note that this
mode is not supported for 3D textures.
See glDetailTexFuncSGIS for more explanation of the detail
texture magnification filters, and glSharpenTexFuncSGIS for
more explanation of the sharpen texture magnification filters.
GL_TEXTURE_MIN_LOD [Toc] [Back]
Sets the minimum level-of-detail parameter. This floatingpoint
value limits the selection of highest resolution mipmap
(lowest mipmap level). The initial value is -1000.
GL_TEXTURE_MAX_LOD [Toc] [Back]
Sets the maximum level-of-detail parameter. This floatingpoint
value limits the selection of the lowest resolution
mipmap (highest mipmap level). The initial value is 1000.
GL_TEXTURE_BASE_LEVEL [Toc] [Back]
Specifies the index of the lowest defined mipmap level. This is
an integer value. The initial value is 0.
GL_TEXTURE_MAX_LEVEL [Toc] [Back]
Sets the index of the highest defined mipmap level. This is an
integer value. The initial value is 1000.
GL_TEXTURE_WRAP_S [Toc] [Back]
Sets the wrap parameter for texture coordinate s to GL_CLAMP,
GL_REPEAT, GL_CLAMP_TO_BORDER_SGIS, or GL_CLAMP_TO_EDGE.
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- , where N is
|2N 2N|
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. GL_CLAMP_TO_BORDER_SGIS is similar to
GL_CLAMP, but the s coordinate range is adjusted slightly to
ensure that the texture border is fully accessed. 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 [Toc] [Back]
Sets the wrap parameter for texture coordinate t to GL_CLAMP,
GL_REPEAT, GL_CLAMP_TO_BORDER_SGIS, or GL_CLAMP_TO_EDGE. See
Page 7
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
the discussion under GL_TEXTURE_WRAP_S. Initially,
GL_TEXTURE_WRAP_T is set to GL_REPEAT.
GL_TEXTURE_WRAP_R [Toc] [Back]
Sets the wrap parameter for texture coordinate r to GL_CLAMP,
GL_REPEAT, GL_CLAMP_TO_BORDER_SGIS, or GL_CLAMP_TO_EDGE. See
the discussion under GL_TEXTURE_WRAP_S. Initially,
GL_TEXTURE_WRAP_R is set to GL_REPEAT.
GL_TEXTURE_WRAP_Q_SGIS [Toc] [Back]
Sets the wrap parameter for texture coordinate q to GL_CLAMP,
GL_REPEAT, or GL_CLAMP_TO_BORDER_SGIS. See the discussion
under GL_TEXTURE_WRAP_S, but note that the q coordinate wraps
only when the SGIS_texture4D extension is being used.
Initially, GL_TEXTURE_WRAP_Q_SGIS is set to GL_REPEAT.
GL_TEXTURE_BORDER_COLOR [Toc] [Back]
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_DETAIL_TEXTURE_LEVEL_SGIS [Toc] [Back]
Specifies the level of the detail texture image. Must be
negative. See glDetailTexFuncSGIS for more information.
GL_DETAIL_TEXTURE_MODE_SGIS [Toc] [Back]
Specifies the detail texture mode. The permissible values are
GL_ADD and GL_MODULATE. See glDetailTexFuncSGIS for more
information.
GL_POST_TEXTURE_FILTER_BIAS_SGIX [Toc] [Back]
GL_POST_TEXTURE_FILTER_SCALE_SGIX [Toc] [Back]
Specifies the bias and scale values for the texture. params
contains four values that comprise the R, G, B, and A bias
terms (in the case of GL_POST_TEXTURE_FILTER_BIAS_SGIX) or
scale factors (in the case of
GL_POST_TEXTURE_FILTER_SCALE_SGIX).
The scale, bias, and clamp to [0, 1] operations are applied, in
that order, directly before the texture environment equations,
or, if the SGI_texture_color_table extension exists, directly
before the texture color lookup table. See glColorTableSGI for
more information about color lookup tables.
GL_TEXTURE_PRIORITY [Toc] [Back]
Specifies the texture residence priority. Permissible values
are in the range [0.0, 1.0]. See glPrioritizeTextures for more
information.
Page 8
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_TEXTURE_BASE_LEVEL_SGIS [Toc] [Back]
GL_TEXTURE_MAX_LEVEL_SGIS [Toc] [Back]
The GL specification describes a ``complete'' set of mipmap
image arrays as array levels 0 through p, where p is a welldefined
function of the dimensions of the level 0 image
discussed under GL_TEXTURE_MIN_FILTER above. The level 0 image
is the base level (the highest-resolution image, with the
largest dimensions), and the level p image is the maximum level
(the lowest-resolution image, with the smallest dimensions, 1
by 1). To be used for texturing, all the levels of the
complete mipmap set must be loaded.
The SGIS_texture_lod extension allows the base and maximum
levels to be redefined - the base level may be set to a value
greater than zero, and the maximum level may be set to a value
less than p. This permits a large texture to be loaded and
used initially at low resolution, and then at higher
resolutions as more data or texture loading time becomes
available. To be used for texturing, only the levels between
the base and maximum (inclusive) must be loaded. (Other levels
may be loaded, but only the levels from base through maximum
will be used.)
When pname is GL_TEXTURE_BASE_LEVEL_SGIS, params specifies the
base level of the mipmap set for the texture designated by
target. The default value is zero.
When pname is GL_TEXTURE_MAX_LEVEL_SGIS, params specifies the
maximum level of the mipmap set for the texture designated by
target. The default value is 1000.
GL_TEXTURE_MIN_LOD_SGIS [Toc] [Back]
GL_TEXTURE_MAX_LOD_SGIS [Toc] [Back]
When pixel fragments are being generated for a textured
primitive, a level-of-detail (LOD) is computed for each
fragment. The LOD is related to the number of texels that
contribute to the color of the fragment, and is used to select
the mipmap levels (see above) that participate in the fragment
color computation.
Normally the LOD is clamped to a range determined by the
filtering method and the base and maximum mipmap levels. When
the application changes the base or maximum mipmap levels, the
LOD range changes discontinuously, and the texture resolution
in rendered scenes appears to ``pop'' to a new value rather
than making a smooth transition. The SGIS_texture_lod
extension allows the LOD to be clamped to an arbitrary userdefined
range instead of the range implied by the base and
maximum mipmap levels. Because this clamping can be varied
continuously, the transition to a higher- or lower-resolution
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
texture can be accomplished smoothly.
When pname is GL_TEXTURE_MIN_LOD_SGIS, params specifies the new
minimum LOD value for the texture designated by target. The
default is -1000.
When pname is GL_TEXTURE_MAX_LOD_SGIS, params specifies the new
maximum LOD value for the texture designated by target. The
default is 1000.
GL_TEXTURE_LOD_BIAS_S_SGIX [Toc] [Back]
GL_TEXTURE_LOD_BIAS_T_SGIX [Toc] [Back]
GL_TEXTURE_LOD_BIAS_R_SGIX [Toc] [Back]
Many textures have very low energy at high frequencies;
however, the LOD calculation has to assume the opposite. The
result is that mapped textures can appear excessively blurry in
one or more diminensions. The SGIX_texture_lod_bias extension
provides user-control over a texture dimension's influence on
the fragment LOD calculation. The bias specifies the number of
LODs (both integer and fractional) which should be added to the
LOD computed for the specified dimension. The fragment's final
LOD is a function of the LODs computed for each texture
dimension.
Some examples where this extension should be used follow.
Textures with non-power-of-two diminensions stretched to the
nearest power-of-two should have a bias between 0 and -1.0,
since the stretching didn't actually add any high frequency
information. Textures from filtered sources such as video are
often overfiltered differently in each dimension, and benefit
from separate negative biases for each dimension. A negative
bias can also be used to reduce one texture dimension's control
on the LOD or bluriness. This is helpful with a texture such as
a road which may appear too blurry when it is repeated many
times in one direction. Finally, a positive bias can be used to
intentionally make a texture appear blurrier.
When pname is GL_TEXTURE_LOD_BIAS_S_SGIX, params specifies bias
to add to the intermediate LOD calculated for the s dimension
designated by target. The default is 0.
When pname is GL_TEXTURE_LOD_BIAS_T_SGIX, params specifies bias
to add to the intermediate LOD calculated for the t dimension
designated by target. The default is 0.
When pname is GL_TEXTURE_LOD_BIAS_R_SGIX, params specifies bias
to add to the intermediate LOD calculated for the r dimension
designated by target. The default is 0.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_TEXTURE_MAX_CLAMP_S_SGIX [Toc] [Back]
GL_TEXTURE_MAX_CLAMP_T_SGIX [Toc] [Back]
GL_TEXTURE_MAX_CLAMP_R_SGIX [Toc] [Back]
Specifies an upper bound for texture coordinate clamping.
Normally texture coordinates are clamped to a maximum of 1.0
when the wrap parameter is set to one of GL_CLAMP,
GL_CLAMP_TO_BORDER_SGIS, or GL_CLAMP_TO_EDGE. The
SGIX_texture_coordinate_clamp extension allows the user to
specify a maximum clamp of any floating point value in the
range [0,1].
When pname is GL_TEXTURE_MAX_CLAMP_S_SGIX, params specifies the
maximum coordinate clamp for the s dimension designated by
target. The default is 1.0.
When pname is GL_TEXTURE_MAX_CLAMP_T_SGIX, params specifies the
maximum coordinate clamp for the t dimension designated by
target. The default is 1.0.
When pname is GL_TEXTURE_MAX_CLAMP_R_SGIX, params specifies the
maximum coordinate clamp for the r dimension designated by
target. The default is 1.0.
GL_DUAL_TEXTURE_SELECT_SGIS [Toc] [Back]
GL_QUAD_TEXTURE_SELECT_SGIS [Toc] [Back]
On some Silicon Graphics machines with hardware texturing,
texel sizes must be a multiple of 16 bits. Most texture
internal formats simply occupy a multiple of 16 bits that is at
least as large as the format requested by the application,
leaving the remaining bits of each texel unused. The GL_DUAL_
and GL_QUAD_ texture internal formats allow multiple textures
with small texels to be packed into the space of a single 16-
bit texture, thus making full use of texture memory. For
example, an 8-bit luminance texture would normally use a full
16 bits of texture memory for each texel, but if the
application chooses the GL_DUAL_LUMINANCE8_SGIS internal
format, then two 8-bit luminance textures can be packed into
the same space.
Some Silicon Graphics machines with hardware texturing do not
have the above texel size restriction, but may benefit from
this extension by loading textures at a faster rate.
When such a texture is active, the application must select
which of the two packed textures will be used for drawing.
params specifies which is selected. For GL_DUAL_ texture
storage formats, params assumes the value 0 or 1. For GL_QUAD_
texture storage formats, params assumes the value 0, 1, 2, or
3. See glTexImage1D, glTexImage2D or glTexImage3DEXT for
Page 11
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
information about loading dual and quad textures.
GL_TEXTURE_CLIPMAP_CENTER_SGIX [Toc] [Back]
A clipmap's region of interest is determined by some aspect of
the application; for example, it may be derived from an
observer's position in a terrain map. The application defines
the center of the region of interest by executing
glTexParameter with pname set to GL_TEXTURE_CLIPMAP_CENTER_SGIX
and params pointing to an array with two elements. The first
element is the s coordinate of the center of the region of
interest in the level 0 texture image, and the second element
is the t coordinate of the center. (Note that the position
(s_center,t_center) at level 0 corresponds to the position
(s_center/2,t_center/2) at level 1, and so on as the level
number increases.) The coordinates of the center may be
changed at any time; for example, as an observer moves over a
terrain map.
GL_TEXTURE_CLIPMAP_FRAME_SGIX [Toc] [Back]
As the center of a clipmap's region of interest changes, it may
become necessary to load new texture image data into levels 0
through B-1 of the clipmap. This can be accomplished by
executing glTexSubImage2DEXT for each of the levels. However,
texture memory in addition to that used for the region of
interest is needed to store the new image data in each level.
This memory can be reserved by executing glTexParameter with
pname set to GL_TEXTURE_CLIPMAP_FRAME_SGIX and params set to a
floating-point value in the range [0,1]. This reserves
params*D_s/2 texels on either side of the region of interest
along the s coordinate, and params*D_t/2 texels on either side
of the region of interest along the t coordinate, where D_s and
D_t are the dimensions of the region of interest in the s and t
directions, respectively. This additional memory is best
considered as a ``frame'' around the region of interest, where
params specifies the size of the frame as a fraction of the
size of the region of interest. The frame width may be changed
at any time.
GL_TEXTURE_CLIPMAP_OFFSET_SGIX [Toc] [Back]
After new texture image data has been loaded into the frame
around a clipmap's region of interest, the region of interest
must be offset to incorporate the new data (and release the
memory occupied by old data that's no longer needed). This is
accomplished by adding offsets to all s and t coordinates used
to access the clipmap. These offsets may force coordinates to
wrap around, so they have the effect of mapping the texture
image and frame onto a torus. This behavior is useful for
continuous roaming through very large texture images. The
offsets are specified by executing glTexParameter with pname
set to GL_TEXTURE_CLIPMAP_OFFSET_SGIX and params pointing to an
array with two elements. The first element is the offset to be
applied to s coordinates for the level 0 image, and the second
Page 12
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
element is the offset to be applied to t coordinates for the
level 0 image. The coordinate offsets may be changed at any
time.
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX [Toc] [Back]
To utilize a texture of greater than GL_MAX_CLIPMAP_DEPTH_SGIX
levels of detail, additional parameters are provided to index
into a clipmap contained within a larger, virtual clipmap.
This clipmap is specified by executing glTexParameter with
pname set to GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX and params
pointing to an array with three elements. The first element,
known as the lod offset, is the level of detail in the virtual
clipmap corresponding to the base level of the smaller clipmap;
the second element is the depth of the smaller clipmap; and the
third element is the depth of the virtual clipmap.
These values can be changed at any time. For example, the
polygons in a scene that span more than
GL_MAX_CLIPMAP_DEPTH_SGIX levels can be divided into smaller
groups of polygons, each of which spans fewer than
GL_MAX_CLIPMAP_DEPTH_SGIX levels. The
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX parameters are set before
the drawing of each group of polygons to ensure they only need
texels that are available in the active subregion of the
virtual clipmap.
Texture coordinates are relative to the base level of the
virtual clipmap, as are the clipmap center and offset (see
GL_TEXTURE_CLIPMAP_CENTER_SGIX and
GL_TEXTURE_CLIPMAP_OFFSET_SGIX above) and the minimum and
maximum levels of detail (see GL_TEXTURE_MIN_LOD_SGIS,
GL_TEXTURE_MAX_LOD_SGIS, GL_TEXTURE_BASE_LEVEL_SGIS, or
GL_TEXTURE_MAX_LEVEL_SGIS above).
Texel address and level of detail generation proceed with the
smaller clipmap precisely as described above for the nonvirtual
clipmap. If the level of detail is such that a level
below the lod offset would be indexed, texture magnification is
performed even though the finer texture information may be
resident in texture memory. Likewise, levels of detail coarser
than the lod offset plus the clipmap depth may demonstrate
aliasing. The application must choose
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX parameters to prevent
unwanted filtering artifacts.
GL_TEXTURE_COMPARE_SGIX [Toc] [Back]
GL_TEXTURE_COMPARE_OPERATOR_SGIX [Toc] [Back]
The SGIX_shadow extension adds a new stage to the texturing
process. Once a texture value has been fetched from texture
memory, it may be compared with the iterated texture r
coordinate to determine if an object is in shadow. The result
Page 13
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
of the comparison, rather than the texture value itself, is
sent to the filtering stage. If the test passes, the object is
considered to be in shadow; the result of the comparison is 0.
If the test fails, the result is 1. When used with textures
that consist of depth values (internal format
GL_DEPTH_COMPONENT16_SGIX, for example) and a properly-chosen
texture matrix, this can be used to implement shadows. The
comparison operation is enabled by executing glTexParameter
with pname set to GL_TEXTURE_COMPARE_SGIX and params set to the
value GL_TRUE. (It is disabled by using the value GL_FALSE.)
The comparison operation is selected by executing
glTexParameter with pname set to
GL_TEXTURE_COMPARE_OPERATOR_SGIX and params set to the value
GL_TEXTURE_LEQUAL_R_SGIX or GL_TEXTURE_GEQUAL_R_SGIX. Note
that the texture values are treated as though they range from
0.0 through 1.0, just like depth values, so the r coordinates
chosen by the application must also fall in that range.
GL_SHADOW_AMBIENT_SGIX [Toc] [Back]
The SGIX_shadow_ambient extension modifies the behavior of the
SGIX_shadow extension slightly. When a texture comparison
implemented by SGIX_shadow passes, SGIX_shadow_ambient causes
the result to be the shadow ambient value rather than zero.
Larger shadow ambient values result in lighter shadows.
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
between the base and maximum levels 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.
A similar consideration applies for clipmaps. The only difference is
that levels 0 through B of the clipmap must have the same dimensions,
rather than varying by a factor of two for each successive level. Note
that the parameter B is never specified explicitly by the application; it
is inferred from the level at which the texture image dimensions stop
changing. (Recall that the dimensions for each level are provided as
arguments to the glTexImage command.)
Page 14
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
The maximum number of levels in a clipmap is limited; the limit can be
determined by calling glGet with argument GL_MAX_CLIPMAP_DEPTH_SGIX.
The maximum number of levels in a virtual clipmap is limited; the limit
can be determined by calling glGet with argument
GL_MAX_CLIPMAP_VIRTUAL_DEPTH_SGIX.
GL_TEXTURE_MIN_LOD_SGIS, GL_TEXTURE_MAX_LOD_SGIS,
GL_TEXTURE_BASE_LEVEL_SGIS, and GL_TEXTURE_MAX_LEVEL_SGIS are part of the
SGIS_texture_lod extension. GL_FILTER4_SGIS is part of the
SGIS_texture_filter4 extension. GL_POST_TEXTURE_FILTER_BIAS_SGIX and
GL_POST_TEXTURE_FILTER_SCALE_SGIX are part of the SGIX_texture_scale_bias
extension. GL_DUAL_TEXTURE_SELECT_SGIS and GL_QUAD_TEXTURE_SELECT_SGIS
are part of the SGIS_texture_select extension.
GL_TEXTURE_CLIPMAP_FRAME_SGIX, GL_TEXTURE_CLIPMAP_CENTER_SGIX,
GL_TEXTURE_CLIPMAP_OFFSET_SGIX, and GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX
are part of the SGIX_clipmap extension. GL_CLAMP_TO_BORDER_SGIS is part
of the SGIS_texture_border_clamp extension. GL_TEXTURE_COMPARE_SGIX and
GL_TEXTURE_COMPARE_OPERATOR_SGIX are part of the SGIX_shadow extension.
GL_SHADOW_AMBIENT_SGIX is part of the SGIX_shadow_ambient extension.
GL_PIXEL_TEX_GEN_Q_CEILING_SGIX, GL_PIXEL_TEX_GEN_Q_FLOOR_SGIX, and
GL_PIXEL_TEX_GEN_Q_ROUND_SGIX are part of the SGIX_impact_pixel_texture
extension. GL_TEXTURE_LOD_BIAS_S_SGIX, GL_TEXTURE_LOD_BIAS_T_SGIX, and
GL_TEXTURE_LOD_BIAS_R_SGIX are part of the SGIX_texture_lod_bias
extension. GL_TEXTURE_MAX_CLAMP_S_SGIX, GL_TEXTURE_MAX_CLAMP_T_SGIX, and
GL_TEXTURE_MAX_CLAMP_S_SGIX are part of the SGIX_texture_coordinate_clamp
extension. See glIntro for more information about using extensions.
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.
GL_INVALID_VALUE is generated if an attempt is made to set
GL_TEXTURE_BASE_LEVEL_SGIS or GL_TEXTURE_MAX_LEVEL_SGIS to a negative
value.
GL_INVALID_VALUE is generated if pname is GL_TEXTURE_CLIPMAP_CENTER_SGIX
and either of the two values specified by params is negative.
GL_INVALID_VALUE is generated if pname is GL_TEXTURE_CLIPMAP_OFFSET_SGIX
and either of the two values specified by params is negative.
GL_INVALID_VALUE is generated if pname is
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX and any of the three values
specified by params is negative.
Page 15
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_INVALID_VALUE is generated if pname is
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX and the sum of the first two values
specified by params is greater than the third.
GL_INVALID_VALUE is generated if pname is GL_TEXTURE_MAX_CLAMP_S_SGIX,
GL_TEXTURE_MAX_CLAMP_T_SGIX, or GL_TEXTURE_MAX_CLAMP_S_SGIX and params is
less than 0 or greater than 1.
glGetIntegerv with argument GL_MAX_CLIPMAP_DEPTH_SGIX
glGetIntegerv with argument GL_MAX_CLIPMAP_VIRTUAL_DEPTH_SGIX
glGetTexParameter
glGetTexLevelParameter
MACHINE DEPENDENCIES
The SGIX_clipmap extension is supported only on InfiniteReality systems.
The following restrictions apply:
1. For best performance, the ``breakpoint'' clipmap level (B) must
be loaded before any other level. The implementation derives
the size of the clipmap from the size of this level, so loading
this level first permits efficient allocation of texture memory.
2. Clipmaps must be square.
3. GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T must be set to
GL_CLAMP_TO_EDGE_SGIS.
4. It is more efficient to set clipmap attributes that affect
texture memory allocation (such as
GL_TEXTURE_CLIPMAP_FRAME_SGIX) before loading the first level of
the clipmap, rather than after loading it.
5. Virtual clipmaps (whose GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX
parameters have been defined) use texture memory inefficiently.
Each level of detail allocates a region of texture memory the
same size as that of a clipped level. Any clipmap whose depth
is less than GL_MAX_CLIPMAP_DEPTH_SGIX should avoid this by not
specifying GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX parameters. An
application can not readback the texture levels whose size is
smaller than that of the clipped level.
6. The depth of the virtual clipmap given in
GL_TEXTURE_CLIPMAP_VIRTUAL_DEPTH_SGIX must be defined before any
texture levels are downloaded, and it can not be changed once it
has been specified. If the application tries to change the
virtual depth, no action is taken.
7. When using virtual clipmaps, an application should not
overcommit texture memory. Doing so will result in undefined
behavior.
Page 16
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
On RealityEngine, RealityEngine2, and VTX systems
GL_DETAIL_TEXTURE_LEVEL_SGIS must be less than or equal to 4.
On High Impact and Maximum Impact systems, the following restrictions
apply to detail texturing:
1. When detail texturing, the GL_TEXTURE_MIN_FILTER must specify
mipmapping; if not, the detail will be effectively disabled.
2. When specifying GL_TEXTURE_MAG_FILTER, the only mode supported
is GL_LINEAR_DETAIL_SGIS.
3. When specifying GL_DETAIL_TEXTURE_MODE_SGIS, the only mode
supported is GL_ADD.
4. When specifying GL_DETAIL_TEXTURE_LEVEL_SGIS, any values outside
of the range [-2..-6] will be clamped to the limits of that
range.
Detail texturing acts as if the mipmap stack were extended by a number of
levels equal to the absolute value of the GL_DETAIL_TEXTURE_LEVEL_SGIS
parameter. The number of normal mipmap levels plus the number of detail
levels must not exceed the maximum number of levels that can be supported
on the hardware. For example, on InfiniteReality systems the maximum
number of levels is 15. A detail texture at level -4 could be supported
on a base texture of size 2K (that is, a base texture with 11 levels) but
not on a base texture that is larger than 2K (one with 12 or more
levels). Failure to observe this constraint causes detail textures to
swim or jitter.
Octane2 VPro systems use the same hardware for the SGIS_detail_texture
extension and the SGIX_texture_scale_bias extension. If the texture
magnification function is one of the detail texture functions, any usersupplied
GL_POST_TEXTURE_FILTER_SCALE_SGIX or
GL_POST_TEXTURE_FILTER_SCALE_SGIX parameters will be ignored.
The SGIX_shadow extension is supported only on InfiniteReality systems.
The SGIX_shadow_ambient extension is supported only on InfiniteReality
systems.
The SGIS_texture_lod extension is supported on Octane2 VPro systems and
High Impact and Maximum Impact systems. On High Impact and Maximum
Impact systems, however, setting the GL_TEXTURE_MAX_LOD_SGIS will have no
effect.
The SGIX_texture_lod_bias extension is supported only on Octane2 VPro
systems and InfiniteReality systems.
GL_CLAMP_TO_BORDER_SGIS is supported only on Octane2 VPro systems and
High Impact and Maximum Impact systems.
Page 17
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_CLAMP_TO_EDGE_SGIS is supported only on Octane2 VPro systems,
InfiniteReality systems, and O2 systems.
Texture borders are not supported on InfiniteReality systems, so the
border width should always be zero. Applications should use the texture
wrap mode GL_CLAMP_TO_EDGE_SGIS to obtain behavior similar to that of
borders.
GL_CLAMP and GL_CLAMP_TO_BORDER_SGIS modes are not supported on O2
systems, and when set will produce the same clamping result as the
GL_CLAMP_TO_EDGE_SGIS wrap mode.
On InfiniteReality systems, if the post-texture filter scale and bias
values are set to values other than the defaults, they are limited to the
range [0.0, 1.0). (note: this range excludes 1.0.) The
SGIX_texture_scale_bias extension is not supported on RealityEngine,
RealityEngine2, and VTX systems or on High Impact and Maximum Impact
systems.
The SGIS_texture_select extension is supported only on InfiniteReality
systems, High Impact and Maximum Impact on Octane systems, and High
Impact and Maximum Impact on Indigo2 systems with the TRAM option card.
The SGIS_texture_filter4 extension is supported only on InfiniteReality
systems.
On InfiniteReality systems, GL_INVALID_VALUE is generated if the value of
the argument n to the command glTexFilterFuncSGIS does not equal the
value of the implementation dependent constant Size, which can be
determined by calling glGetTexParameter with argument
GL_TEXTURE_FILTER4_SIZE_SGIS. This restriction will be removed in a
future release.
GL_TEXTURE_MAX_CLAMP_S_SGIX, GL_TEXTURE_MAX_CLAMP_T_SGIX, and
GL_TEXTURE_MAX_CLAMP_S_SGIX are only supported on Octane2 VPro systems.
glDetailTexFuncSGIS, glDrawPixels, glBindTexture, glCopyPixels,
glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D,
glCopyTexSubImage2D, glCopyTexSubImage3D, glPixelStore, glPixelTexGen,
glPixelTransfer, glPrioritizeTextures, glSharpenTexFuncSGIS, glTexEnv,
glTexFilterFuncSGIS, glTexGen, glTexImage1D, glTexImage2D, glTexImage3D,
glTexSubImage1D, glTexSubImage2D, glTexSubImage3D
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