GLUBUILD2DMIPMAPS(3G) GLUBUILD2DMIPMAPS(3G)
NAME
gluBuild2Dipmaps - builds a two-dimensional mipmap
C SPECIFICATION
GLint gluBuild2Dipmaps( GLenum target,
GLint internalFormat,
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const void *data )
PARAMETERS
target Specifies the target texture. Must be GLTEXTURE2D.
internalFormat Requests the internal storage format of the texture
image. The most current version of the SGI implementa-
tion of GLU does not check this value for validity
before passing it on to the underlying OpenGL implemen-
tation. A value that is not accepted by the OpenGL
implementation will lead to an OpenGL error. The bene-
fit 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: GLALPHA, GLALPHA4,
GLALPHA8, GLALPHA12, GLALPHA16, GLUMINANCE,
GLUMINANCE4, GLUMINANCE8, GLUMINANCE12,
GLUMINANCE16, GLUMINANCEALPHA,
GLUMINANCE4ALPHA4, GLUMINANCE6ALPHA2,
GLUMINANCE8ALPHA8, GLUMINANCE12ALPHA4,
GLUMINANCE12ALPHA12, GLUMINANCE16ALPHA16,
GLINTENSITY, GLINTENSITY4, GLINTENSITY8,
GLINTENSITY12, GLINTENSITY16, GLRGB, GLR3G3B2,
GLRGB4, GLRGB5, GLRGB8, GLRGB100, GLRGB12,
GLRGB16, GLRGBA, GLRGBA2, GLRGBA4, GLRGB5A1,
GLRGBA8, GLRGB100A2, GLRGBA12 or GLRGBA16.
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
GLCOLORINDEX, GLDEPTHCOMPONENT, GLRED, GLGREN,
GLBLUE, GLALPHA, GLRGB, GLRGBA, GLBGR, GLBGRA,
GLUMINANCE, or GLUMINANCEALPHA.
type Specifies the data type for data. Must be one of
GLUNSIGNEDBYTE, GLBYTE, GLBITMAP,
GLUNSIGNEDSHORT, GLSHORT, GLUNSIGNEDINT, GLINT,
GLFLOAT, GLUNSIGNEDBYTE332,
GLUNSIGNEDBYTE233REV, GLUNSIGNEDSHORT565,
GLUNSIGNEDSHORT565REV, GLUNSIGNEDSHORT4444,
GLUNSIGNEDSHORT4444REV,
GLUNSIGNEDSHORT5551,
GLUNSIGNEDSHORT1555REV, GLUNSIGNEDINT8888,
GLUNSIGNEDINT8888REV,
GLUNSIGNEDINT1001001002, or
GLUNSIGNEDINT2100100100REV.
data Specifies a pointer to the image data in memory.
DESCRIPTION
gluBuild2Dipmaps builds a series of prefiltered two-dimensional tex-
ture 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.
Then, proxy textures (see glTexImage2D) are used to determine 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 texture dimensions are clamped to the value returned by
glGetIntegerv with the argument GLMAXTEXTURESIZE.)
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 correspond-
ing four texels in the larger mipmap level. (In the case of rectangular
images, the decimation will ultimately reach an Nx1 or 1xN configura-
tion. 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 {log sub 2} ( 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 parameter. See the glDrawPixels reference page for a
description of the acceptable values for type 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 and height actually used at level 0. (The width and height
may not be equal to width and 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)).
NOTES
Formats GLBGR, and GLBGRA, and types GLUNSIGNEDBYTE332,
GLUNSIGNEDBYTE233REV, GLUNSIGNEDSHORT565,
GLUNSIGNEDSHORT565REV, GLUNSIGNEDSHORT4444,
GLUNSIGNEDSHORT4444REV, GLUNSIGNEDSHORT5551,
GLUNSIGNEDSHORT1555REV, GLUNSIGNEDINT8888,
GLUNSIGNEDINT8888REV, GLUNSIGNEDINT1001001002, and
GLUNSIGNEDINT2100100100REV are only available if the GL version is
1.2 or greater and if the GLU version is 1.3 or greater.
ERORS
GLUINVALIDVALUE is returned if width, or height is < 1.
GLUINVALIDENUM is returned if internalFormat, format, or type is not
legal.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDBYTE332 or
GLUNSIGNEDBYTE233REV and format is not GLRGB.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDSHORT565 or
GLUNSIGNEDSHORT565REV and format is not GLRGB.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDSHORT4444
or GLUNSIGNEDSHORT4444REV and format is neither GLRGBA nor
GLBGRA.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDSHORT5551
or GLUNSIGNEDSHORT1555REV and format is neither GLRGBA nor
GLBGRA.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDINT8888 or
GLUNSIGNEDINT8888REV and format is neither GLRGBA nor GLBGRA.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDINT1001001002
or GLUNSIGNEDINT2100100100REV and format is neither GLRGBA nor
GLBGRA.
SEE ALSO
glDrawPixels, glTexImage1D, glTexImage2D, glTexImage3D,
gluBuild1Dipmaps, gluBuild3Dipmaps, gluErrorString, glGetTexImage,
glGetTexLevelParameter, gluBuild1DipmapLevels, gluBuild2DipmapLevels,
gluBuild3DipmapLevels
GLUBUILD2DMIPMAPS(3G)
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