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_BIAS GL_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);
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_BIAS GL_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()
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. m[blue]http://opencontent.org/openpub/m[].