NAME
gluBuild1DMipmaps - builds a 1-D mipmap
C SPECIFICATION
GLint gluBuild1DMipmaps( GLenum target,
GLint internalFormat,
GLsizei width,
GLenum format,
GLenum type,
const void *data )
PARAMETERS
target Specifies the target texture. Must be
GL_TEXTURE_1D.
internalFormat 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.
width Specifies the width, in pixels, of the
texture image.
format 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.
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, or GL_FLOAT.
data Specifies a pointer to the image data in
memory.
DESCRIPTION
gluBuild1DMipmaps builds a series of prefiltered 1-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 of data is checked to see if it is 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 is exactly between powers of 2, then the copy of data
will scale upwards.) For example, if width is 57 then a
copy of data will scale up to 64 before mipmapping takes
place.
Then, proxy textures (see glTexImage1D) are used to
determine if the implementation can fit the requested
texture. If not, width is continually halved until it fits.
Next, a series of mipmap levels is built by decimating a
copy of data in half until size 1 is reached. At each level,
each texel in the halved mipmap level is an average of the
corresponding two texels in the larger mipmap level.
glTexImage1D is called to load each of these mipmap levels.
Level 0 is a copy of data. The highest level is log2(width).
For example, if width is 64 and the implementation can store
a texture of this size, the following mipmap levels are
built: 64x1, 32x1, 16x1, 8x1, 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 type. See the glDrawPixels reference
page for a description of the acceptable values for data.
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 actually
used at level 0. (The width may not be equal to width since
proxy textures might have scaled it to fit the
implementation.) Then the maximum level can be derived from
the formula log2(width).
ERRORS
GLU_INVALID_VALUE is returned if width is < 1.
GLU_INVALID_ENUM is returned if internalFormat, format or
type are not legal.
SEE ALSO
glDrawPixels, glTexImage1D, glTexImage2D, gluBuild2DMipmaps,
gluErrorString, gluScaleImage