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Man Pages


Manual Reference Pages  -  GLUBUILD1DMIPMAPS (3)

NAME

gluBuild1DMipmaps - builds a 1-D mipmap

CONTENTS

C Specification
Parameters
Description
Notes
Errors
See Also

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
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