Difference between revisions of "GLAPI/glSamplerParameter"

Core in version 4.6 3.3 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 ${\displaystyle \left[{\tfrac {-1}{2N}},1+{\tfrac {1}{2N}}\right]}$, 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 ${\displaystyle \left[{\tfrac {1}{2N}},1-{\tfrac {1}{2N}}\right]}$, 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: ${\displaystyle min(1-{\tfrac {1}{2*N}},max({\tfrac {1}{2*N}},abs(coord)))}$. 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 ${\displaystyle result={\begin{cases}1.0,&r\leq D_{t}\\0.0,&r>D_{t}\end{cases}}}$
GL_GEQUAL ${\displaystyle result={\begin{cases}1.0,&r\geq D_{t}\\0.0,&r
GL_LESS ${\displaystyle result={\begin{cases}1.0,&r
GL_GREATER ${\displaystyle result={\begin{cases}1.0,&r>D_{t}\\0.0,&r\leq D_{t}\end{cases}}}$
GL_EQUAL ${\displaystyle result={\begin{cases}1.0,&r=D_{t}\\0.0,&r\neq D_{t}\end{cases}}}$
GL_NOTEQUAL ${\displaystyle result={\begin{cases}1.0,&r\neq D_{t}\\0.0,&r=D_{t}\end{cases}}}$
GL_ALWAYS ${\displaystyle result=1.0}$
GL_NEVER ${\displaystyle result=0.0}$

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.

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.