gltexparameter - Man Page
glTexParameter(3G) OpenGL Reference 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 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_WRAP_S, GL_TEXTURE_WRAP_T,
GL_TEXTURE_WRAP_R_EXT, GL_TEXTURE_WRAP_Q_SGIS,
GL_DETAIL_TEXTURE_LEVEL_SGIS, GL_DETAIL_TEXTURE_MODE_SGIS,
GL_TEXTURE_PRIORITY_EXT, GL_TEXTURE_BASE_LEVEL_SGIS,
GL_TEXTURE_MAX_LEVEL_SGIS, GL_TEXTURE_MIN_LOD_SGIS,
GL_TEXTURE_MAX_LOD_SGIS, 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.
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, GL_DETAIL_TEXTURE_2D_SGIS, or GL_TEXTURE_3D_EXT.
GL_TEXTURE_4D_SGIS.
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_WRAP_R_EXT,
Page 1
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_TEXTURE_WRAP_Q_SGIS, 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_PRIORITY_EXT, GL_TEXTURE_BASE_LEVEL_SGIS,
GL_TEXTURE_MAX_LEVEL_SGIS, GL_TEXTURE_MIN_LOD_SGIS,
GL_TEXTURE_MAX_LOD_SGIS, 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_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.
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, 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 in param (or values in params) to the
texture parameter specified by pname. target defines the target texture:
GL_TEXTURE_1D, GL_TEXTURE_2D, GL_DETAIL_TEXTURE_2D_SGIS, or
GL_TEXTURE_3D_EXT. 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 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
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, subsequent mipmaps have
dimension 1 x 2**(l-1) or 2**(k-1) x 1 until the final mipmap,
which has dimension 1 x 1. Mipmaps are defined using
glTexImage1D, glTexImage2D or glTexImage3DEXT with the level-
of-detail argument indicating the order of the mipmaps. Level
0 is the original texture; level max(n,m) is the final 1 x 1
mipmap.
Page 2
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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. (See below for
more information.) Note that clipmaps may be used only with
borderless 2D textures.
param 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_EXT, 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
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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 two-
pass 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.
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.
Page 4
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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 default 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 any 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_EXT, 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
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.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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 two-
pass 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.
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.
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
default value of GL_TEXTURE_MAG_FILTER is GL_LINEAR.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
See glDetailTexFuncSGIS for more explanation of the detail
texture magnification filters, and glSharpenTexFuncSGIS for
more explanation of the sharpen texture magnification filters.
GL_TEXTURE_WRAP_S
Sets the wrap parameter for texture coordinate s to GL_CLAMP,
GL_REPEAT, GL_CLAMP_TO_BORDER_SGIS, or GL_CLAMP_TO_EDGE_SGIS.
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.
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. GL_CLAMP_TO_EDGE_SGIS is
also similar to GL_CLAMP, but the s coordinate range is
adjusted slightly to ensure that the texture border is never
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
Sets the wrap parameter for texture coordinate t to GL_CLAMP,
GL_REPEAT, GL_CLAMP_TO_BORDER_SGIS, or GL_CLAMP_TO_EDGE_SGIS.
See the discussion under GL_TEXTURE_WRAP_S. Initially,
GL_TEXTURE_WRAP_T is set to GL_REPEAT.
GL_TEXTURE_WRAP_R_EXT
Sets the wrap parameter for texture coordinate r to GL_CLAMP,
GL_REPEAT, or GL_CLAMP_TO_EDGE_SGIS. See the discussion under
GL_TEXTURE_WRAP_S. Initially, GL_TEXTURE_WRAP_R_EXT 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_DETAIL_TEXTURE_LEVEL_SGIS
Specifies the level of the detail texture image. Must be
negative. See glDetailTexFuncSGIS for more information.
GL_DETAIL_TEXTURE_MODE_SGIS
Specifies the detail texture mode. The permissible values are
GL_ADD and GL_MODULATE. See glDetailTexFuncSGIS for more
information.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
GL_POST_TEXTURE_FILTER_BIAS_SGIX
Specifies the bias values for the texture. params contains four
values that comprise the R, G, B, and A bias factors.
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.
GL_POST_TEXTURE_FILTER_SCALE_SGIX
Specifies the scale values for the texture. params contains
four values that comprise the R, G, B, and A scale factors.
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.
GL_TEXTURE_PRIORITY_EXT
Specifies the texture residence priority. Permissible values
are in the range [0.0, 1.0]. See glPrioritizeTexturesEXT for
more information.
GL_TEXTURE_BASE_LEVEL_SGIS
GL_TEXTURE_MAX_LEVEL_SGIS
The GL specification describes a ``complete'' set of mipmap
image arrays as array levels 0 through p, where p is a well-
defined 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, param specifies the
base level of the mipmap set for the texture designated by
target. The default value is zero.
Page 8
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
When pname is GL_TEXTURE_MAX_LEVEL_SGIS, param specifies the
maximum level of the mipmap set for the texture designated by
target. The default value is 1000.
GL_TEXTURE_MIN_LOD_SGIS
GL_TEXTURE_MAX_LOD_SGIS
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 user-
defined 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
texture can be accomplished smoothly.
When pname is GL_TEXTURE_MIN_LOD_SGIS, param specifies the new
minimum LOD value for the texture designated by target. The
default is -1000.
When pname is GL_TEXTURE_MAX_LOD_SGIS, param specifies the new
maximum LOD value for the texture designated by target. The
default is 1000.
GL_DUAL_TEXTURE_SELECT_SGIS
GL_QUAD_TEXTURE_SELECT_SGIS
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.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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.
param specifies which is selected. For GL_DUAL_ texture
storage formats, param assumes the value 0 or 1. For GL_QUAD_
texture storage formats, param assumes the value 0, 1, 2, or 3.
See glTexImage1D, glTexImage2D or glTexImage3DEXT for
information about loading dual and quad textures.
GL_TEXTURE_CLIPMAP_CENTER_SGIX
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
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 param set to a
floating-point value in the range [0,1]. This reserves
param*D_s/2 texels on either side of the region of interest
along the s coordinate, and param*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
param 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
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
Page 10
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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
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_COMPARE_SGIX
GL_TEXTURE_COMPARE_OPERATOR_SGIX
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
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_COMPONENT, 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 param 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 param 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
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.
NOTES
Linear filtering accesses the four nearest texture elements only in 2D
textures. In 1D textures, linear filtering accesses the two nearest
texture elements. In 3D textures, linear filtering accesses the eight
nearest texture elements.
Page 11
glTexParameter(3G) OpenGL Reference glTexParameter(3G)
Suppose texturing is enabled (by calling glEnable with argument
GL_TEXTURE_1D, GL_TEXTURE_2D, or GL_TEXTURE_3D_EXT) and
GL_TEXTURE_MIN_FILTER is set 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, or glTexImage3DEXT)
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.
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.)
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.
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_TEXTURE_PRIORITY_EXT is part of the
EXT_texture_object 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, and
GL_TEXTURE_CLIPMAP_OFFSET_SGIX are part of the SGIX_clipmap extension.
GL_CLAMP_TO_EDGE_SGIS is part of the SGIS_texture_edge_clamp 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. See glIntro for more
information about using extensions.
ERRORS
GL_INVALID_ENUM is generated when target or pname is not one of the
accepted defined values, or when param should have a defined constant
value (based on the value of pname) and does not.
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.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
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_OPERATION is generated if glTexParameter is executed between
the execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGetIntegerv with argument GL_MAX_CLIPMAP_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.
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 specifying GL_TEXTURE_MAG_FILTER, the only mode supported
is GL_LINEAR_DETAIL_SGIS.
2. When specifying GL_DETAIL_TEXTURE_MODE_SGIS, the only mode
supported is GL_ADD.
3. When specifying GL_DETAIL_TEXTURE_LEVEL_SGIS, any values outside
of the range [-2..-6] will be clamped to the limits of that
range.
The SGIX_shadow extension is supported only on InfiniteReality systems.
The SGIX_shadow_ambient extension is supported only on InfiniteReality
systems.
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glTexParameter(3G) OpenGL Reference glTexParameter(3G)
The SGIS_texture_lod extension is supported High Impact and Maximum
Impact systems; however, setting the GL_TEXTURE_MAX_LOD_SGIS will have no
effect.
GL_CLAMP_TO_BORDER_SGIS is supported only on High Impact and Maximum
Impact systems.
GL_CLAMP_TO_EDGE_SGIS is supported only on InfiniteReality systems.
Texture borders are not supported on InfiniteReality systems, so the
border width should always be zero. Borders will be supported in future
releases. However, borders use texture memory very inefficiently; up to
four times the memory required by the base texture may be needed to
support borders properly. Whenever possible, applications should use the
texture wrap mode GL_CLAMP_TO_EDGE_SGIS and borderless textures. This
might be essential for large textures, which otherwise won't fit in
texture memory because of the border overhead.
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 and on High Impact and Maximum Impact 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.
There is a known problem with shadow textures and texture binding on
InfiniteReality systems. After using a shadow texture, applications
should disable shadowing (by calling glTexParameter with argument
GL_TEXTURE_COMPARE_SGIX and value GL_FALSE) before binding any other
texture. This will be fixed in the next release.
SEE ALSO
glDetailTexFuncSGIS, glIntro, glSharpenTexFuncSGIS,
glPrioritizeTexturesEXT, glTexEnv, glTexFilterFuncSGIS, glTexImage1D,
glTexImage2D, glTexImage3DEXT, glTexGen. glPixelTexGen.
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