GLAPI/glSamplerParameter

From OpenGL.org
Jump to: navigation, search
glSamplerParameter
Core in version 4.4
Core since version 3.3
Core ARB extension ARB_sampler_objects

glSamplerParameter: set sampler parameters

Function Definition

 void glSamplerParameterf(GLuint sampler​, GLenum pname​, GLfloat param​);
 void glSamplerParameteri(GLuint sampler​, GLenum pname​, GLint param​);
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​.

Function Definition

 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​);
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_LOD_BIAS​
params​ specifies a fixed bias value that is to be added to the level-of-detail parameter for the texture before texture sampling. The specified value is added to the shader-supplied bias value (if any) and subsequently clamped into the implementation-defined range [-biasmax, biasmax], where biasmax is the value of the implementation defined constant GL_MAX_TEXTURE_LOD_BIAS​. The initial value is 0.0.
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 2n × 2m, there are max(n, m) + 1 mipmaps. The first mipmap is the original texture, with dimensions 2n × 2m. Each subsequent mipmap has dimensions 2k - 1 × 2l - 1, where 2k × 2l are the dimensions of the previous mipmap, until either k or l. At that point, subsequent mipmaps have dimension 1 × 2l - 1 or 2k - 1 × 1 until the final mipmap, which has dimension 1 × 1. 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_BORDER​, GL_CLAMP_TO_EDGE​, GL_MIRRORED_REPEAT​, GL_MIRROR_CLAMP_TO_EDGE​, or GL_REPEAT​. GL_CLAMP_TO_BORDER​ causes the s coordinate to be clamped to the range \left [ \tfrac{-1}{2N}, 1 + \tfrac{1}{2N} \right ], 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 \left [ \tfrac{1}{2N}, 1 - \tfrac{1}{2N} \right ], where N is the size of the texture in the direction of clamping. GL_REPEAT​ causes the integer part of the s coordinate to be ignored; the GL uses only the fractional part, thereby creating a repeating pattern. 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. GL_MIRROR_CLAMP_TO_EDGE​ causes the s coordinate to be clamped as follows: min(1-\tfrac{1}{2*N}, max(\tfrac{1}{2*N}, abs(coord))). 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_BORDER​, GL_CLAMP_TO_EDGE​, GL_MIRRORED_REPEAT​, GL_MIRROR_CLAMP_TO_EDGE​, or GL_REPEAT​. See the discussion under GL_TEXTURE_WRAP_S​. Initially, GL_TEXTURE_WRAP_T​ is set to GL_REPEAT​.
GL_TEXTURE_WRAP_R​
Sets the wrap parameter for texture coordinate r to either GL_CLAMP_TO_BORDER​, GL_CLAMP_TO_EDGE​, GL_MIRRORED_REPEAT​, GL_MIRROR_CLAMP_TO_EDGE​, or GL_REPEAT​. See the discussion under GL_TEXTURE_WRAP_S​. Initially, GL_TEXTURE_WRAP_R​ is set to GL_REPEAT​.
GL_TEXTURE_BORDER_COLOR​
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).
If the I form of glTexParameter or glSamplerParameter are used, and GL_TEXTURE_BORDER_COLOR​ is specified, then the data are stored as signed or unsigned integer values, as is the appropriate type. When not using the I forms, the values are converted to floating-point.
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​ result = 
\begin{cases}
 1.0, & r \le D_t\\
 0.0, & r > D_t
\end{cases}
GL_GEQUAL​ result = 
\begin{cases}
 1.0, & r \ge D_t\\
 0.0, & r < D_t
\end{cases}
GL_LESS​ result = 
\begin{cases}
 1.0, & r < D_t\\
 0.0, & r \ge D_t
\end{cases}
GL_GREATER​ result = 
\begin{cases}
 1.0, & r > D_t\\
 0.0, & r \le D_t
\end{cases}
GL_EQUAL​ result = 
\begin{cases}
 1.0, & r = D_t\\
 0.0, & r \ne D_t
\end{cases}
GL_NOTEQUAL​ result = 
\begin{cases}
 1.0, & r \ne D_t\\
 0.0, & r = D_t
\end{cases}
GL_ALWAYS​ result = 1.0
GL_NEVER​ result = 0.0


where r is the current interpolated texture coordinate, and Dt is the texture value sampled from the currently bound texture. result is assigned to Rt.


When the ParameterI​ forms of the function are used with GL_TEXTURE_BORDER_COLOR​, the border color is stored as an integer value, not a floating-point value.

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.

GL_MIRROR_CLAMP_TO_EDGE​ is available only if the GL version is 4.4 or greater.

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, 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/.