gluBuild2DMipmaps()gluBuild2DMipmaps()NAMEgluBuild2DMipmaps - builds a 2-D mipmap
SYNOPSIS
GLint gluBuild2DMipmaps(
GLenum target,
GLint internalFormat,
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const void *data );
PARAMETERS
Specifies the target texture. Must be GL_TEXTURE_2D. Requests the
internal storage format of the texture image. Must be 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_INTEN‐
SITY16, 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. Specifies the width and height,
respectively, in pixels of the texture image. 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_LUMI‐
NANCE_ALPHA. 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. Specifies a pointer to the image
data in memory.
DESCRIPTIONgluBuild2DMipmaps() builds a series of prefiltered 2-D texture maps of
decreasing resolutions called a mipmap. This is used for the antialias‐
ing 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 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 and down to 16, respectively, 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 1x1 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 rec‐
tangular 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 log[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 accept‐
able 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 glGetTexLevelParameter(). 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 log[2](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 ALSOglDrawPixels(3), glTexImage1D(3), glTexImage2D(3),
gluBuild1DMipmaps(3), gluErrorString(3), gluScaleImage(3)gluBuild2DMipmaps()
