Name

gluBuild2DMipmapLevels - builds a subset of two-dimensional mipmap levels

C Specification

GLint gluBuild2DMipmapLevels(GLenum target,
GLint internalFormat,
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
GLint level,
GLint base,
GLint max,
const void*   data);

Parameters

target

Specifies the target texture. Must be GL_TEXTURE_2D.

internalFormat

Requests the internal storage format of the texture image. The most current version of the implementation of GLU ES does not check this value for validity before passing it on to the underlying OpenGL ES implementation. A value that is not accepted by the OpenGL ES implementation will lead to an OpenGL ES error. The benefit of not checking this value at the GLU level is that OpenGL ES extensions can add new internal texture formats without requiring a revision of the GLU implementation. Older implementations of GLU ES check this value and raise a GLU ES error if it is not one of the following symbolic constants: GL_ALPHA, GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB or GL_RGBA.

width, height

Specifies the width and height, respectively, in pixels of the texture image. These should be a power of 2.

format

Specifies the format of the pixel data. Must be one of GL_ALPHA, GL_RGB, GL_RGBA, GL_LUMINANCE or GL_LUMINANCE_ALPHA.

type

Specifies the data type for data. Must be one of GL_UNSIGNED_BYTE, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_4_4_4_4 or GL_UNSIGNED_SHORT_5_5_5_1.

level

Specifies the mipmap level of the image data.

base

Specifies the minimum mipmap level to pass to glTexImage2D.

max

Specifies the maximum mipmap level to pass to glTexImage2D.

data

Specifies a pointer to the image data in memory.

Description

gluBuild2DMipmapLevels builds a subset 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).

A series of mipmap levels from base to max is built by decimating data in half along both dimensions until size 1 x 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 x 1 or 1 x N configuration. Here, two texels are averaged instead.) glTexImage2D is called to load these mipmap levels from base to max. If max is larger than the highest mipmap level for the texture of the specified size, then a GLU error code is returned (see gluErrorString) and nothing is loaded.

For example, if level is 2 and width is 16 and height is 8, the following levels are possible: 16 x 8, 8 x 4, 4 x 2, 2 x 1, 1 x 1. These correspond to levels 2 through 6 respectively. If base is 3 and max is 5, then only mipmap levels 8 x 4, 4 x 2, and 2 x 1 are loaded. However, if max is 7, then an error is returned and nothing is loaded since max is larger than the highest mipmap level which is, in this case, 6.

The highest mipmap level can be derived from the formula log2(max(width, height) * 2^level).

Notes

gluBuild2DMipmapLevels is only available if the GLU ES version is 1.3 or greater.

Errors

GLU_INVALID_VALUE is returned if level > base, base < 0, max < base, or max is > the highest mipmap level for data.

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 GL_UNSIGNED_SHORT_5_6_5 and format is not GL_RGB.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_4_4_4_4 and format is not GL_RGBA.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_5_5_1 and format is not GL_RGBA.

See Also

gluBuild2DMipmaps, gluErrorString.

Copyright

Copyright c 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/.