glTexParameterf, glTexParameteri, glTexParameterfv, glTexParameteriv

[New - Windows 95, OEM Service Release 2]

These functions set texture parameters.

void glTexParameterf(

void glTexParameteri(

Parameters

target

The target texture, which must be either GL_TEXTURE_1D or GL_TEXTURE_2D.

pname

The symbolic name of a single-valued texture parameter. 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^nx2^m there are max(n, m) + 1 mipmaps. The first mipmap is the original texture, with dimensions 2^nx2^m. Each subsequent mipmap has dimensions 2^k-1x2^l-1 where 2^kx2^l are the dimensions of the previous mipmap, until either k = 0 or l = 0. At that point, subsequent mipmaps have dimension 1x2^l-1 or 2^k-1x1 until the final mipmap, which has dimension 1x1. Mipmaps are defined using glTexImage1D or glTexImage2D with the level-of-detail argument indicating the order of the mipmaps. Level 0 is the original texture; level bold max(n, m) is the final 1x1 mipmap.

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.

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; OpenGL 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.

param

The value of pname.

void glTexParameterfv(

void glTexParameteriv(

Parameters

target

The target texture, which must be either GL_TEXTURE_1D or GL_TEXTURE_2D.

pname

The symbolic name of a texture parameter. 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^nx2^m there are max(n, m) + 1 mipmaps. The first mipmap is the original texture, with dimensions 2^nx2^m. Each subsequent mipmap has dimensions 2^k-1x2^l-1 where 2^kx2^l are the dimensions of the previous mipmap, until either k = 0 or l = 0. At that point, subsequent mipmaps have dimension 1x2^l-1 or 2^k-1x1 until the final mipmap, which has dimension 1x1. Mipmaps are defined using glTexImage1D or glTexImage2D with the level-of-detail argument indicating the order of the mipmaps. Level 0 is the original texture; level bold max(n, m) is the final 1x1 mipmap.

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.

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; OpenGL 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. The params parameter 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).

params

A pointer to an array where the value or values of pname are stored. The params parameter 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, GL_TEXTURE_WRAP_T, and on the exact mapping. 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 default value of GL_TEXTURE_MAG_FILTER is GL_LINEAR.

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.

Remarks

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.

The glTexParameter function assigns the value or values in params to the texture parameter specified as pname. The target parameter defines the target texture, either GL_TEXTURE_1D or GL_TEXTURE_2D.

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 default value of GL_TEXTURE_MIN_FILTER is GL_NEAREST_MIPMAP_LINEAR.

Suppose texturing is enabled (by calling glEnable with argument GL_TEXTURE_1D or GL_TEXTURE_2D) and GL_TEXTURE_MIN_FILTER is set to one of the functions that requires a mipmap. If either the dimensions of the texture images currently defined (with previous calls to glTexImage1D or glTexImage2D) do not follow the proper sequence for mipmaps, 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 2-D textures. In 1-D textures, linear filtering accesses the two nearest texture elements.

The following function retrieves information related to glTexParameterf, glTexParameteri, glTexParameterfv, and glTexParameteriv:

glGetTexParameterDPEWNY

Error Codes

The following are the error codes generated and their conditions.

See Also