GLTEXPARAMETER(3G)

NAME
glTexParameter - set texture parameters

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, GL_TEXTURE_2D, GL_TEXTURE_3D, or GL_TEXTURE_CUBE_MAP.

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_MIN_LOD, GL_TEXTURE_MAX_LOD, GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL, GL_TEXTURE_WRAP_S, GL_TEXTURE_WRAP_T, GL_TEXTURE_WRAP_R, GL_TEXTURE_PRIORITY, GL_TEXTURE_COMPARE_MODE, GL_TEXTURE_COMPARE_FUNC, GL_DEPTH_TEXTURE_MODE, or GL_GENERATE_MIPMAP.

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, GL_TEXTURE_2D or GL_TEXTURE_3D.

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_MIN_LOD, GL_TEXTURE_MAX_LOD, GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL, GL_TEXTURE_WRAP_S, GL_TEXTURE_WRAP_T, GL_TEXTURE_WRAP_R, GL_TEXTURE_BORDER_COLOR, GL_TEXTURE_PRIORITY, GL_TEXTURE_COMPARE_MODE, GL_TEXTURE_COMPARE_FUNC, GL_DEPTH_TEXTURE_MODE, or GL_GENERATE_MIPMAP.

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, GL_TEXTURE_2D, or GL_TEXTURE_3D. 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_BASE_LEVEL
    Specifies the index of the lowest defined mipmap level. This is an integer value. The initial value is 0.

GL_TEXTURE_MAX_LEVEL
    Sets the index of the highest defined mipmap level. This is an integer value. The initial value is 1000.

GL_TEXTURE_WRAP_S
    Sets the wrap parameter for texture coordinate s to either GL_CLAMP, GL_CLAMP_TO_BORDER, GL_CLAMP_TO_EDGE, GL_MIRRORED_REPEAT, 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_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. Border texture elements are accessed only if wrapping is set to GL_CLAMP or GL_CLAMP_TO_BORDER. 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, GL_CLAMP_TO_BORDER, 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, GL_CLAMP_TO_BORDER, 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
    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.

GL_TEXTURE_COMPARE_MODE
    Specifies the texture comparison mode for currently bound depth textures. That is, a texture whose internal format is GL_DEPTH_COMPONENT_*; see glTexImage2D()) Permissible values are:

    GL_COMPARE_R_TO_TEXTURE
        Specifies that the interpolated and clamped r texture coordinate should be compared to the value in the currently bound depth 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 luminance, intensity, or alpha (as specified by GL_DEPTH_TEXTURE_MODE).

    GL_NONE
        Specifies that the luminance, intensity, or alpha (as specified by GL_DEPTH_TEXTURE_MODE) should be assigned the appropriate value from the currently bound depth texture.

GL_TEXTURE_COMPARE_FUNC
    Specifies the comparison operator used when GL_TEXTURE_COMPARE_MODE is set to GL_COMPARE_R_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 depth texture value sampled from the currently bound depth texture. result is assigned to the either the luminance, intensity, or alpha (as specified by GL_DEPTH_TEXTURE_MODE.)

GL_DEPTH_TEXTURE_MODE
    Specifies a single symbolic constant indicating how depth values should be treated during filtering and texture application. Accepted values are GL_LUMINANCE, GL_INTENSITY, and GL_ALPHA. The initial value is GL_LUMINANCE.

GL_GENERATE_MIPMAP
    Specifies a boolean value that indicates if all levels of a mipmap array should be automatically updated when any modification to the base level mipmap is done. The initial value is GL_FALSE.

NOTES

GL_TEXTURE_3D, GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD, GL_CLAMP_TO_EDGE, GL_TEXTURE_BASE_LEVEL, and GL_TEXTURE_MAX_LEVEL are available only if the GL version is 1.2 or greater.

GL_CLAMP_TO_BORDER is available only if the GL version is 1.3 or greater.

GL_MIRRORED_REPEAT, GL_TEXTURE_COMPARE_MODE, GL_TEXTURE_COMPARE_FUNC, GL_DEPTH_TEXTURE_MODE, and GL_GENERATE_MIPMAP are available only if the GL version is 1.4 or greater.

GL_TEXTURE_COMPARE_FUNC allows the following additional comparison modes only if the GL version is 1.5 or greater: GL_LESS, GL_GREATER, GL_EQUAL, GL_NOTEQUAL, GL_ALWAYS, and GL_NEVER.

Suppose that a program has enabled texturing (by calling glEnable() with argument GL_TEXTURE_1D, GL_TEXTURE_2D, or GL_TEXTURE_3D) 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(), glTexImage3D(), 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.

For OpenGL versions 1.3 and greater, or when the ARB_multitexture extension is supported, glTexParameter specifies the texture parameters for the active texture unit, specified by calling glActiveTexture().

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

glActiveTexture(), glBindTexture(), glCopyPixels(), glCopyTexImage1D(), glCopyTexImage2D(), glCopyTexSubImage1D(), glCopyTexSubImage2D(), glCopyTexSubImage3D(), glDrawPixels(), glPixelStore(), glPixelTransfer(), glPrioritizeTextures(), glTexEnv(), glTexGen(), glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubImage1D(), glTexSubImage2D(), glTexSubImage3D()

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.