gluBuild2DMipmaps
GLUBUILD2DMIPMAPS(3G) GLUBUILD2DMIPMAPS(3G)
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 of the texture image.
The most current version of the SGI implementation of
GLU does not check this value for validity before
passing it on to the underlying OpenGL implementation.
A value that is not accepted by the OpenGL implementa-
tion will lead to an OpenGL error. The benefit of not
checking this value at the GLU level is that OpenGL
extensions can add new internal texture formats with-
out 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: 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 in pixels the width and height, respec-
tively, of the texture image.
format Specifies the of the pixel data. Must be one of
GL_COLOR_INDEX, GL_DEPTH_COMPONENT, GL_RED, GL_GREEN,
GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_BGR, GL_BGRA,
GL_LUMINANCE, or 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,
GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2,
GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5,
GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4,
GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1,
GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, or
GL_UNSIGNED_INT_2_10_10_10_REV.
data Specifies a pointer to the image data in memory.
DESCRIPTION
gluBuild2DMipmaps 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 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 1×1 is reached. At each
level, each texel in the halved mipmap level is an average of the cor-
responding four texels in the larger mipmap level. (In the case of
rectangular images, the decimation will ultimately reach an N×1 or 1×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)). 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:
64×16, 32×8, 16×4, 8×2, 4×1, 2×1 and 1×1. These correspond to levels 0
through 6, respectively.
See the glTexImage1D reference page for a description of the accept-
able 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 GL_BGR, and GL_BGRA, and types GL_UNSIGNED_BYTE_3_3_2,
GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5,
GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4,
GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1,
GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8,
GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, and
GL_UNSIGNED_INT_2_10_10_10_REV are only available if the GL version is
1.2 or greater and if the GLU version is 1.3 or greater.
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_BYTE_3_3_2 or
GL_UNSIGNED_BYTE_2_3_3_REV and format is not GL_RGB.
GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_6_5
or GL_UNSIGNED_SHORT_5_6_5_REV and format is not GL_RGB.
GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_4_4_4_4
or GL_UNSIGNED_SHORT_4_4_4_4_REV and format is neither GL_RGBA nor
GL_BGRA.
GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_5_5_1
or GL_UNSIGNED_SHORT_1_5_5_5_REV and format is neither GL_RGBA nor
GL_BGRA.
GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_INT_8_8_8_8
or GL_UNSIGNED_INT_8_8_8_8_REV and format is neither GL_RGBA nor
GL_BGRA.
GLU_INVALID_OPERATION is returned if type is
GL_UNSIGNED_INT_10_10_10_2 or GL_UNSIGNED_INT_2_10_10_10_REV and for-
mat is neither GL_RGBA nor GL_BGRA.
SEE ALSO
glDrawPixels(3G), glTexImage1D(3G), glTexImage2D(3G), glTexIm-
age3D(3G), gluBuild1DMipmaps(3G), gluBuild3DMipmaps(3G),
gluErrorString(3G), glGetTexImage(3G), glGetTexLevelParameter(3G),
gluBuild1DMipmapLevels(3G), gluBuild2DMipmapLevels(3G),
gluBuild3DMipmapLevels(3G)
GLUBUILD2DMIPMAPS(3G)
