NAME¶
glSamplerParameter - set sampler parameters
C SPECIFICATION¶
void
glSamplerParameterf(GLuint sampler,
GLenum pname,
GLfloat param);
void
glSamplerParameteri(GLuint sampler,
GLenum pname,
GLint param);
PARAMETERS¶
sampler
Specifies the sampler object whose parameter to
modify.
pname
Specifies the symbolic name of a single-valued sampler
parameter. pname can be one of the following: GL_TEXTURE_WRAP_S,
GL_TEXTURE_WRAP_T, GL_TEXTURE_WRAP_R,
GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER,
GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD,
GL_TEXTURE_LOD_BIASGL_TEXTURE_COMPARE_MODE, or
GL_TEXTURE_COMPARE_FUNC.
param
Specifies the value of pname.
C SPECIFICATION¶
void
glSamplerParameterfv(GLuint sampler,
GLenum pname,
const GLfloat * params);
void
glSamplerParameteriv(GLuint sampler,
GLenum pname,
const GLint * params);
void
glSamplerParameterIiv(GLuint sampler,
GLenum pname,
const GLint *params);
void
glSamplerParameterIuiv(GLuint sampler,
GLenum pname,
const GLuint *params);
PARAMETERS¶
sampler
Specifies the sampler object whose parameter to
modify.
pname
Specifies the symbolic name of a sampler parameter.
pname can be one of the following: GL_TEXTURE_WRAP_S,
GL_TEXTURE_WRAP_T, GL_TEXTURE_WRAP_R,
GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER,
GL_TEXTURE_BORDER_COLOR, GL_TEXTURE_MIN_LOD,
GL_TEXTURE_MAX_LOD,
GL_TEXTURE_LOD_BIASGL_TEXTURE_COMPARE_MODE, or
GL_TEXTURE_COMPARE_FUNC.
params
Specifies a pointer to an array where the value or values
of pname are stored.
DESCRIPTION¶
glSamplerParameter assigns the value or values in
params to the sampler parameter specified as pname.
sampler specifies the sampler object to be modified, and must be the
name of a sampler object previously returned from a call to
glGenSamplers(). 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 n
× 2 m, there are max n m + 1 mipmaps. The first mipmap is
the original texture, with dimensions 2 n × 2 m. Each subsequent
mipmap has dimensions 2 k - 1 × 2 l - 1, where 2 k × 2 l are
the dimensions of the previous mipmap, until either k = 0 or l = 0. At that
point, subsequent mipmaps have dimension 1 × 2 l - 1 or 2 k - 1
× 1 until the final mipmap, which has dimension 1 × 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 × 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_WRAP_S
Sets the wrap parameter for texture coordinate s to
either GL_CLAMP_TO_EDGE, GL_MIRRORED_REPEAT, or
GL_REPEAT. GL_CLAMP_TO_BORDER causes the s coordinate to be
clamped to the range -1 2N 1 + 1 2N, where N is the size of the texture in the
direction of clamping.GL_CLAMP_TO_EDGE causes s coordinates to be
clamped to the range 1 2N 1 - 1 2N, 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. GL_MIRRORED_REPEAT causes the s
coordinate to be set to the fractional part of the texture coordinate if the
integer part of s is even; if the integer part of s is odd, then the s texture
coordinate is set to 1 - frac s, where frac s represents the
fractional part of s. 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_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 r to
either 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
The data in params specifies four values that
define the border values that should be used for border texels. If a texel is
sampled from the border of the texture, the values of
GL_TEXTURE_BORDER_COLOR are interpreted as an RGBA color to match the
texture's internal format and substituted for the non-existent texel data. If
the texture contains depth components, the first component of
GL_TEXTURE_BORDER_COLOR is interpreted as a depth value. The initial
value is 0.0, 0.0, 0.0, 0.0.
GL_TEXTURE_COMPARE_MODE
Specifies the texture comparison mode for currently bound
textures. That is, a texture whose internal format is
GL_DEPTH_COMPONENT_*; see
glTexImage2D()) Permissible values
are:
GL_COMPARE_REF_TO_TEXTURE
Specifies that the interpolated and clamped r texture
coordinate should be compared to the value in the currently bound texture. See
the discussion of GL_TEXTURE_COMPARE_FUNC for details of how the
comparison is evaluated. The result of the comparison is assigned to the red
channel.
GL_NONE
Specifies that the red channel should be assigned the
appropriate value from the currently bound texture.
GL_TEXTURE_COMPARE_FUNC
Specifies the comparison operator used when
GL_TEXTURE_COMPARE_MODE is set to
GL_COMPARE_REF_TO_TEXTURE.
Permissible values are:
| Texture Comparison Function |
Computed result |
| GL_LEQUAL |
<div> result = 1.0 0.0 r <= D t r >
D t </div> |
| GL_GEQUAL |
<div> result = 1.0 0.0 r >= D t r <
D t </div> |
| GL_LESS |
<div> result = 1.0 0.0 r < D t r >=
D t </div> |
| GL_GREATER |
<div> result = 1.0 0.0 r > D t r <=
D t </div> |
| GL_EQUAL |
<div> result = 1.0 0.0 r = D t r ≠
D t </div> |
| GL_NOTEQUAL |
<div> result = 1.0 0.0 r ≠ D t r =
D t </div> |
| GL_ALWAYS |
<div> result = 1.0 </div> |
| GL_NEVER |
<div> result = 0.0 </div> |
where r is the current interpolated texture coordinate, and D t is
the texture value sampled from the currently bound texture. result is
assigned to R t.
NOTES¶
glSamplerParameter is available only if the GL version is
3.3 or higher.
If a sampler object is bound to a texture unit and that unit is
used to sample from a texture, the parameters in the sampler are used to
sample from the texture, rather than the equivalent parameters in the
texture object bound to that unit. This introduces the possibility of
sampling from the same texture object with different sets of sampler state,
which may lead to a condition where a texture is incomplete with
respect to one sampler object and not with respect to another. Thus,
completeness can be considered a function of a sampler object and a texture
object bound to a single texture unit, rather than a property of the texture
object itself.
ERRORS¶
GL_INVALID_VALUE is generated if sampler is not the
name of a sampler object previously returned from a call to
glGenSamplers().
GL_INVALID_ENUM is generated if params should have a
defined constant value (based on the value of pname) and does
not.
ASSOCIATED GETS¶
glGetSamplerParameter()
SEE ALSO¶
glGenSamplers(), glBindSampler(),
glDeleteSamplers(), glIsSampler(), glBindTexture(),
glTexParameter()
COPYRIGHT¶
Copyright © 2010 Khronos Group. This material may be
distributed subject to the terms and conditions set forth in the Open
Publication License, v 1.0, 8 June 1999.
http://opencontent.org/openpub/.