gluBuild2DMipmaps(3G) OpenGL Reference gluBuild2DMipmaps(3G)
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 )
PARAMETERS
target Specifies the target texture. Must be GLTEXTURE2D.
internalFormat Requests the internal storage format of the texture
image. Must be 1, 2, 3, or 4 or one of the following
symbolic constants: GLALPHA, GLALPHA4, GLALPHA8,
GLALPHA12, GLALPHA16, GLLUMINANCE, GLLUMINANCE4,
GLLUMINANCE8, GLLUMINANCE12, GLLUMINANCE16,
GLLUMINANCEALPHA, GLLUMINANCE4ALPHA4,
GLLUMINANCE6ALPHA2, GLLUMINANCE8ALPHA8,
GLLUMINANCE12ALPHA4, GLLUMINANCE12ALPHA12,
GLLUMINANCE16ALPHA16, GLINTENSITY, GLINTENSITY4,
GLINTENSITY8, GLINTENSITY12, GLINTENSITY16, GLRGB,
GLRGB2EXT, GLR3G3B2, GLRGB4, GLRGB5, GLRGB8,
GLRGB10, GLRGB12, GLRGB16, GLRGBA, GLRGBA2,
GLRGBA4, GLRGB5A1, GLRGBA8, GLRGB10A2, GLRGBA12 or
GLRGBA16.
width, height Specifies the width and height, respectively, in pixels
of the texture image.
format Specifies the format of the pixel data. Must be one of:
GLCOLORINDEX, GLDEPTHCOMPONENT, GLRED, GLGREEN,
GLBLUE, GLALPHA, GLRGB, GLRGBA, GLLUMINANCE,
GLLUMINANCEALPHA and GLABGREXT.
type Specifies the data type for data. Must be one of:
GLUNSIGNEDBYTE, GLBYTE, GLBITMAP, GLUNSIGNEDSHORT,
GLSHORT, GLUNSIGNEDINT, GLINT, GLFLOAT,
GLUNSIGNEDBYTE332EXT,
GLUNSIGNEDSHORT4444EXT,
GLUNSIGNEDSHORT5551EXT,
GLUNSIGNEDINT8888EXT, and
GLUNSIGNEDINT1010102EXT.
data Specifies a pointer to the image data in memory.
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gluBuild2DMipmaps(3G) OpenGL Reference gluBuild2DMipmaps(3G)
DESCRIPTION
gluBuild2DMipmaps builds a series of prefiltered 2-D texture 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 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 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 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 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: 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 & 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
GLUINVALIDVALUE is returned if width or height are < 1.
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gluBuild2DMipmaps(3G) OpenGL Reference gluBuild2DMipmaps(3G)
GLUINVALIDENUM is returned if internalFormat, format or type are not
legal.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDBYTE332EXT
and format is not GLRGB.
GLUINVALIDOPERATION is returned if type is
GLUNSIGNEDSHORT4444EXT and format is neither GLRGBA nor
GLABGREXT.
GLUINVALIDOPERATION is returned if type is
GLUNSIGNEDSHORT5551EXT and format is neither GLRGBA nor
GLABGREXT.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDINT8888EXT
and format is neither GLRGBA nor GLABGREXT.
GLUINVALIDOPERATION is returned if type is
GLUNSIGNEDINT1010102EXT and format is neither GLRGBA nor
GLABGREXT.
GLUINVALIDOPERATION is returned if format is GLABGREXT and the
GLEXTabgr extension is not supported.
GLUINVALIDOPERATION is returned if type is GLUNSIGNEDBYTE332EXT,
GLUNSIGNEDSHORT4444EXT, GLUNSIGNEDSHORT5551EXT,
GLUNSIGNEDINT8888EXT or GLUNSIGNEDINT1010102EXT and the
GLEXTpackedpixels extension is not supported.
GLUINVALIDOPERATION is returned if format is GLDEPTHCOMPONENT and the
GLSGIXdepthtexture extension is not supported.
SEE ALSO
glDrawPixels, glTexImage1D, glTexImage2D, gluBuild1DMipmaps,
gluErrorString, glGetTexImage, glGetTexLevelParameter.
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