gluBuild2DMipmaps() gluBuild2DMipmaps()
gluBuild2DMipmaps - builds a 2-D mipmap
GLint gluBuild2DMipmaps(
GLenum target,
GLint internalFormat,
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const void *data );
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_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.
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_LUMINANCE_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.
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 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 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
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 acceptable values for format. See the glDrawPixels()
reference page for a description of the acceptable values
for type.
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)).
GLU_INVALID_VALUE is returned if width or height are < 1.
GLU_INVALID_ENUM is returned if internalFormat, format or
type are not legal.
glDrawPixels(3), glTexImage1D(3), glTexImage2D(3),
gluBuild1DMipmaps(3), gluErrorString(3), gluScaleImage(3)
gluBuild2DMipmaps()
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