GLUBUILD2DMIPMAPS()MachTen Programmer’s ManualGLUBUILD2DMIPMAPS()

NAME
gluBuild2DMipmaps - builds a 2-D mipmap

C SPECIFICATION
GLint gluBuild2DMipmaps( GLenum target,
GLint internalFormat,
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const void *data )

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PARAMETERS
target Specifies the target texture. Must be
GL_TEXTURE_2D.

internalFormat Requests the internal storage format of
the texture image. Must be 1, 2, 3, or 4
or one of the following symbolic con-
stants: GL_ALPHA, GL_ALPHA4, GL_ALPHA8,
GL_ALPHA12, GL_ALPHA16, GL_LUMINANCE,
GL_LUMINANCE4, GL_LUMINANCE8,
GL_LUMINANCE12, GL_LUMINANCE16,
GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4,
GL_LUMINANCE6_ALPHA2,
GL_LUMINANCE8_ALPHA8,
GL_LUMINANCE12_ALPHA4,
GL_LUMINANCE12_ALPHA12,
GL_LUMINANCE16_ALPHA16, GL_INTENSITY,
GL_INTENSITY4, GL_INTENSITY8,
GL_INTENSITY12, GL_INTENSITY16, GL_RGB,
GL_R3_G3_B2, GL_RGB4, GL_RGB5, GL_RGB8,
GL_RGB10, GL_RGB12, GL_RGB16, GL_RGBA,
GL_RGBA2, GL_RGBA4, GL_RGB5_A1, GL_RGBA8,
GL_RGB10_A2, GL_RGBA12 or GL_RGBA16.

width, height Specifies the width and height, respec-
tively, in pixels of the texture image.

format Specifies the format of the pixel data.
Must be one of: GL_COLOR_INDEX, GL_RED,
GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB,
GL_RGBA, GL_LUMINANCE, and
GL_LUMINANCE_ALPHA.

type Specifies the data type for data. Must be
one of: GL_UNSIGNED_BYTE, GL_BYTE,
GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT,
GL_UNSIGNED_INT, GL_INT, or GL_FLOAT.

data Specifies a pointer to the image data in
memory.

DESCRIPTION
gluBuild2DMipmaps builds a series of prefiltered 2-D tex-
ture maps of decreasing resolutions called a mipmap. This
is used for the antialiasing of texture mapped primitives.

A return value of 0 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 two. If not, a copy of data (not
data), is scaled up or down to the nearest power of two.
This copy will be used for subsequent mipmapping opera-
tions 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 and down to 16,
respectively, before mipmapping takes place.

Then, proxy textures (see glTexImage2D) are used to deter-
mine 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 tex-
ture dimensions are clamped to the value returned by
glGetIntegerv with the argument GL_MAX_TEXTURE_SIZE.)

Next, a series of mipmap levels is built by decimating a
copy of data in half along both dimensions until size 1x1
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 lev-
els. Level 0 is a copy of data. The highest level is
log2(max(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: 64x16,
32x8, 16x4, 8x2, 4x1, 2x1 and 1x1. These correspond to
levels 0 through 6, respectively.

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

NOTES
Note that there is no direct way of querying the maximum
level. This can be derived indirectly via glGetTexLevelPa-
rameter. First, query for the width & height actually used
at level 0. (The width & height may not be equal to width
& height respectively since proxy textures might have
scaled them to fit the implementation.) Then the maximum
level can be derived from the formula
log2(max(width,height)).

ERRORS
GLU_INVALID_VALUE is returned if width or height are < 1.

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

SEE ALSO
glDrawPixels, glTexImage1D, glTexImage2D,
gluBuild1DMipmaps,
gluErrorString, gluScaleImage

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