Name

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 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 ES level is that OpenGL ES extensions can add new internal texture formats without requiring a revision of the GLU ES 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 in pixels the width and height, respectively, of the texture image.

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.

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.

Next, a series of mipmap levels is built by decimating a copy of 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 each of these mipmap levels. Level 0 is a copy of data. The highest level is log2(max(width, height) * 2^level). 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 x 16, 32 x 8, 16 x 4, 8 x 2, 4 x 1, 2 x 1, 1 x 1. These correspond to levels 0 through 6, respectively.

See the glTexImage2D reference page for a description of the acceptable values for format parameter.

Notes

Note that there is no direct way of querying the maximum level. First, query for the width and height actually used at level 0. Then the maximum level can be derived from the formula log2(max(width, height) * 2^level).

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 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

gluBuild2DMipmapLevels, 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/.