GLUBUILD1DMIPMAPS()MachTen Programmer’s ManualGLUBUILD1DMIPMAPS()

NAME
gluBuild1DMipmaps - builds a 1-D mipmap

C SPECIFICATION
GLint gluBuild1DMipmaps( GLenum target,
GLint internalFormat,
GLsizei width,
GLenum format,
GLenum type,
const void *data )

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PARAMETERS
target Specifies the target texture. Must be
GL_TEXTURE_1D.

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 Specifies the width, 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
gluBuild1DMipmaps builds a series of prefiltered 1-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 of data is checked to see if it is 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 operations described below.
(If width is exactly between powers of 2, then the copy of
data will scale upwards.) 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 deter-
mine 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 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 lev-
els. Level 0 is a copy of data. The highest level is
log2(width). For example, if width is 64 and the imple-
mentation can store a texture of this size, the following
mipmap levels are built: 64x1, 32x1, 16x1, 8x1, 4x1, 2x1
and 1x1. These correspond to levels 0 through 6, respec-
tively.

See the glTexImage1D reference page for a description of
the acceptable values for type. See the glDrawPixels ref-
erence page for a description of the acceptable values for
data.

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 actually used at level
0. (The width may not be equal to width since proxy tex-
tures might have scaled it to fit the implementation.)
Then the maximum level can be derived from the formula
log2(width).

ERRORS
GLU_INVALID_VALUE is returned if width is < 1.

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

SEE ALSO
glDrawPixels, glTexImage1D, glTexImage2D,
gluBuild2DMipmaps,
gluErrorString, gluScaleImage

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