GLUBUILD1DMIPMAPS(3gl)GLUBUILD1DMIPMAPS(3gl)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_LUMI‐
NANCE_ALPHA, GL_LUMINANCE4_ALPHA4, GL_LUMI‐
NANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8, GL_LUMI‐
NANCE12_ALPHA4, GL_LUMINANCE12_ALPHA12, GL_LUMI‐
NANCE16_ALPHA16, GL_INTENSITY, GL_INTENSITY4, GL_INTEN‐
SITY8, 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 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 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 opera‐
tions 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 continu‐
ally 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 implementa‐
tion.) 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
15 Mar 97 GLUBUILD1DMIPMAPS(3gl)
