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Man Pages


Manual Reference Pages  -  GLTEXPARAMETERIV (3)

NAME

glTexParameterf, glTexParameteri, glTexParameterfv, glTexParameteriv - set texture parameters

CONTENTS

C Specification
Parameters
C Specification
Parameters
Description
Notes
Errors
Associated Gets
See Also

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 or GL_TEXTURE_2D.
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, or GL_TEXTURE_PRIORITY.
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 or GL_TEXTURE_2D.
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_BORDER_COLOR, or GL_TEXTURE_PRIORITY.
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) coordinate system. A texture is a one- or two-dimensional image and a set of parameters that determine how samples are derived from the image.

glTexParameter assigns the value or values in params to the texture parameter specified as pname. target defines the target texture, either GL_TEXTURE_1D or GL_TEXTURE_2D. 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 2ntimes2m, there are max(n,m)+1 mipmaps. The first mipmap is the original texture, with dimensions 2ntimes2m. Each subsequent mipmap has dimensions 2k-1times2l-1, where 2ktimes2l are the dimensions of the previous mipmap, until either k=0 or l=0. At that point, subsequent mipmaps have dimension 1times2l-1 or 2k-1times1 until the final mipmap, which has dimension 1times1. To define the mipmaps, call glTexImage1D, glTexImage2D, 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 1times1 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_WRAP_S
  Sets the wrap parameter for texture coordinate s to either GL_CLAMP or GL_REPEAT. 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. 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 either GL_CLAMP or GL_REPEAT. See the discussion under GL_TEXTURE_WRAP_S. Initially, GL_TEXTURE_WRAP_T 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_TEXTURE_PRIORITY
  Specifies the texture residence priority of the currently bound texture. Permissible values are in the range [0, 1]. See glPrioritizeTextures and glBindTexture for more information.

NOTES

Suppose that a program has enabled texturing (by calling glEnable with argument GL_TEXTURE_1D or GL_TEXTURE_2D) and has set GL_TEXTURE_MIN_FILTER 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, glCopyTexImage1D, or glCopyTexImage2D) do not follow the proper sequence for mipmaps (described above), or there are fewer texture images defined than are needed, or the set of texture images have differing numbers of texture components, then it is as if texture mapping were disabled.

Linear filtering accesses the four nearest texture elements only in 2D textures. In 1D textures, linear filtering accesses the two nearest texture elements.

ERRORS

GL_INVALID_ENUM is generated if target or pname is not one of the accepted defined values.

GL_INVALID_ENUM is generated if params should have a defined constant value (based on the value of pname) and does not.

GL_INVALID_OPERATION is generated if glTexParameter is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

glGetTexParameter
glGetTexLevelParameter

SEE ALSO

glBindTexture, glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glDrawPixels, glPixelStore, glPixelTransfer, glPrioritizeTextures, glTexEnv, glTexGen, glTexImage1D, glTexImage2D, glTexSubImage1D, glTexSubImage2D

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