1991-2006
Silicon Graphics, Inc.
gluBuild1DMipmaps
3G

# gluBuild1DMipmaps

builds a one-dimensional mipmap

## C Specification

                    GLint gluBuild1DMipmaps
                    GLenum target
                    GLint internalFormat
                    GLsizei width
                    GLenum format
                    GLenum type
                    const void * data

## Parameters

`target`

  Specifies the target texture. Must be `GLU_TEXTURE_1D`.

`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`

  Specifies the width, in pixels, 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

`gluBuild1DMipmaps` builds a series of prefiltered one-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` of `data` is checked to see if it is a power of 2. If not, a copy of `data` is scaled up or down to the nearest power of 2. (If `width` is exactly between powers of 2, then the copy of `data` will scale upwards.) This copy will be used for subsequent mipmapping operations described below. For example, if `width` is 57, then a copy of `data` will scale up to 64 before mipmapping takes place.

Then, proxy textures (see glTexImage1D) are used to determine if the implementation can fit the requested texture. If not, `width` is continually halved until it fits.

Next, a series of mipmap levels is built by decimating a copy of `data` in half until size 1 × 1 is reached. At each level, each texel in the halved mipmap level is an average of the corresponding two texels in the larger mipmap level.

glTexImage1D is called to load each of these mipmap levels. Level 0 is a copy of `data`. The highest level is log 2 &af; width . For example, if `width` is 64 and the implementation can store a texture of this size, the following mipmap levels are built: 64 × 1 , 32 × 1 , 16 × 1 , 8 × 1 , 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 the `type` parameter. See the glDrawPixels reference page for a description of the acceptable values for the `data` 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 actually used at level 0. (The width may not be equal to `width` since proxy textures might have scaled it to fit the implementation.) Then the maximum level can be derived from the formula log 2 &af; width .

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` is < 1.

`GLU_INVALID_ENUM` is returned if `format` or `type` are 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, gluBuild2DMipmapLevels, gluBuild2DMipmaps, 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/.