1991-2006
Silicon Graphics, Inc.
gluBuild2DMipmaps
3G

# gluBuild2DMipmaps

builds a two-dimensional mipmap

## C Specification

                    GLint gluBuild2DMipmaps
                    GLenum target
                    GLint internalFormat
                    GLsizei width
                    GLsizei height
                    GLenum format
                    GLenum type
                    const void * data

## Parameters

`target`

  Specifies the target texture. Must be `GLU_TEXTURE_2D`.

`internalFormat`

  Requests the internal storage format of the texture image. The most current version of the SGI implementation of GLU does not check this value for validity before passing it on to the underlying OpenGL implementation. A value that is not accepted by the OpenGL implementation will lead to an OpenGL error. The benefit of not checking this value at the GLU level is that OpenGL extensions can add new internal texture formats without requiring a revision of the GLU implementation. Older implementations of GLU check this value and raise a GLU error if it is not 1, 2, 3, or 4 or one of the following symbolic constants: `GLU_ALPHA`, `GLU_ALPHA4`, `GLU_ALPHA8`, `GLU_ALPHA12`, `GLU_ALPHA16`, `GLU_LUMINANCE`, `GLU_LUMINANCE4`, `GLU_LUMINANCE8`, `GLU_LUMINANCE12`, `GLU_LUMINANCE16`, `GLU_LUMINANCE_ALPHA`, `GLU_LUMINANCE4_ALPHA4`, `GLU_LUMINANCE6_ALPHA2`, `GLU_LUMINANCE8_ALPHA8`, `GLU_LUMINANCE12_ALPHA4`, `GLU_LUMINANCE12_ALPHA12`, `GLU_LUMINANCE16_ALPHA16`, `GLU_INTENSITY`, `GLU_INTENSITY4`, `GLU_INTENSITY8`, `GLU_INTENSITY12`, `GLU_INTENSITY16`, `GLU_RGB`, `GLU_R3_G3_B2`, `GLU_RGB4`, `GLU_RGB5`, `GLU_RGB8`, `GLU_RGB10`, `GLU_RGB12`, `GLU_RGB16`, `GLU_RGBA`, `GLU_RGBA2`, `GLU_RGBA4`, `GLU_RGB5_A1`, `GLU_RGBA8`, `GLU_RGB10_A2`, `GLU_RGBA12`, or `GLU_RGBA16`.

`width`
`height`

  Specifies in pixels the width and height, respectively, of the texture image.

`format`

  Specifies the format of the pixel data. Must be one of `GLU_COLOR_INDEX`, `GLU_DEPTH_COMPONENT`, `GLU_RED`, `GLU_GREEN`, `GLU_BLUE`, `GLU_ALPHA`, `GLU_RGB`, `GLU_RGBA`, `GLU_BGR`, `GLU_BGRA`, `GLU_LUMINANCE`, or `GLU_LUMINANCE_ALPHA`.

`type`

  Specifies the data type for `data`. Must be one of `GLU_UNSIGNED_BYTE`, `GLU_BYTE`, `GLU_BITMAP`, `GLU_UNSIGNED_SHORT`, `GLU_SHORT`, `GLU_UNSIGNED_INT`, `GLU_INT`, `GLU_FLOAT`, `GLU_UNSIGNED_BYTE_3_3_2`, `GLU_UNSIGNED_BYTE_2_3_3_REV`, `GLU_UNSIGNED_SHORT_5_6_5`, `GLU_UNSIGNED_SHORT_5_6_5_REV`, `GLU_UNSIGNED_SHORT_4_4_4_4`, `GLU_UNSIGNED_SHORT_4_4_4_4_REV`, `GLU_UNSIGNED_SHORT_5_5_5_1`, `GLU_UNSIGNED_SHORT_1_5_5_5_REV`, `GLU_UNSIGNED_INT_8_8_8_8`, `GLU_UNSIGNED_INT_8_8_8_8_REV`, `GLU_UNSIGNED_INT_10_10_10_2`, or `GLU_UNSIGNED_INT_2_10_10_10_REV`.

`data`

  Specifies a pointer to the image data in memory.

## Description

`gluBuild2DMipmaps` builds a series of prefiltered two-dimensional texture maps of decreasing resolutions called a mipmap. This is used for the antialiasing of texture-mapped primitives.

A return value of zero indicates success, otherwise a GLU error code is returned (see gluErrorString).

Initially, the `width` and `height` of `data` are checked to see if they are a power of 2. If not, a copy of `data` (not `data`), is scaled up or down to the nearest power of 2. This copy will be used for subsequent mipmapping operations described below. (If `width` or `height` is exactly between powers of 2, then the copy of `data` will scale upwards.) For example, if `width` is 57 and `height` is 23, then a copy of `data` will scale up to 64 in `width` and down to 16 in depth, before mipmapping takes place.

Then, proxy textures (see glTexImage2D) are used to determine if the implementation can fit the requested texture. If not, both dimensions are continually halved until it fits. (If the OpenGL version is \(<= 1.0, both maximum texture dimensions are clamped to the value returned by glGetIntegerv with the argument `GLU_MAX_TEXTURE_SIZE`.)

Next, a series of mipmap levels is built by decimating a copy of `data` in half along both dimensions until size 1 × 1 is reached. At each level, each texel in the halved mipmap level is an average of the corresponding four texels in the larger mipmap level. (In the case of rectangular images, the decimation will ultimately reach an N × 1 or 1 × N configuration. Here, two texels are averaged instead.)

glTexImage2D is called to load each of these mipmap levels. Level 0 is a copy of `data`. The highest level is log 2 &af; max &af; width height . For example, if `width` is 64 and `height` is 16 and the implementation can store a texture of this size, the following mipmap levels are built: 64 × 16 , 32 × 8 , 16 × 4 , 8 × 2 , 4 × 1 , 2 × 1 , and 1 × 1 These correspond to levels 0 through 6, respectively.

See the glTexImage1D reference page for a description of the acceptable values for `format` parameter. See the glDrawPixels reference page for a description of the acceptable values for `type` parameter.

## Notes

Note that there is no direct way of querying the maximum level. This can be derived indirectly via glGetTexLevelParameter. First, query for the width and height actually used at level 0. (The width and height may not be equal to `width` and `height` respectively since proxy textures might have scaled them to fit the implementation.) Then the maximum level can be derived from the formula log 2 &af; max &af; width height .

Formats `GLU_BGR`, and `GLU_BGRA`, and types `GLU_UNSIGNED_BYTE_3_3_2`, `GLU_UNSIGNED_BYTE_2_3_3_REV`, `GLU_UNSIGNED_SHORT_5_6_5`, `GLU_UNSIGNED_SHORT_5_6_5_REV`, `GLU_UNSIGNED_SHORT_4_4_4_4`, `GLU_UNSIGNED_SHORT_4_4_4_4_REV`, `GLU_UNSIGNED_SHORT_5_5_5_1`, `GLU_UNSIGNED_SHORT_1_5_5_5_REV`, `GLU_UNSIGNED_INT_8_8_8_8`, `GLU_UNSIGNED_INT_8_8_8_8_REV`, `GLU_UNSIGNED_INT_10_10_10_2`, and `GLU_UNSIGNED_INT_2_10_10_10_REV` are only available if the GL version is 1.2 or greater and if the GLU version is 1.3 or greater.

## Errors

`GLU_INVALID_VALUE` is returned if `width` or `height` is < 1.

`GLU_INVALID_ENUM` is returned if `internalFormat`, `format`, or `type` is not legal.

`GLU_INVALID_OPERATION` is returned if `type` is `GLU_UNSIGNED_BYTE_3_3_2` or `GLU_UNSIGNED_BYTE_2_3_3_REV` and `format` is not `GLU_RGB`.

`GLU_INVALID_OPERATION` is returned if `type` is `GLU_UNSIGNED_SHORT_5_6_5` or `GLU_UNSIGNED_SHORT_5_6_5_REV` and `format` is not `GLU_RGB`.

`GLU_INVALID_OPERATION` is returned if `type` is `GLU_UNSIGNED_SHORT_4_4_4_4` or `GLU_UNSIGNED_SHORT_4_4_4_4_REV` and `format` is neither `GLU_RGBA` nor `GLU_BGRA`.

`GLU_INVALID_OPERATION` is returned if `type` is `GLU_UNSIGNED_SHORT_5_5_5_1` or `GLU_UNSIGNED_SHORT_1_5_5_5_REV` and `format` is neither `GLU_RGBA` nor `GLU_BGRA`.

`GLU_INVALID_OPERATION` is returned if `type` is `GLU_UNSIGNED_INT_8_8_8_8` or `GLU_UNSIGNED_INT_8_8_8_8_REV` and `format` is neither `GLU_RGBA` nor `GLU_BGRA`.

`GLU_INVALID_OPERATION` is returned if `type` is `GLU_UNSIGNED_INT_10_10_10_2` or `GLU_UNSIGNED_INT_2_10_10_10_REV` and `format` is neither `GLU_RGBA` nor `GLU_BGRA`.

## See Also

gluBuild1DMipmapLevels, gluBuild1DMipmaps, gluBuild2DMipmapLevels, gluBuild3DMipmapLevels, gluBuild3DMipmaps, gluErrorString, glDrawPixels, glGetTexImage, glGetTexLevelParameter, glTexImage1D, glTexImage2D, glTexImage3D

## 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/.