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Man Pages


Manual Reference Pages  -  GLUBUILD2DMIPMAPS (3)

NAME

gluBuild2DMipmaps - builds a 2-D mipmap

CONTENTS

C Specification
Parameters
Description
Notes
Errors
See Also

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 GL_TEXTURE_2D.
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, 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: 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

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 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. See the glDrawPixels reference page for a description of the acceptable values for type.

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

GLU_INVALID_VALUE is returned if width or height are < 1.

GLU_INVALID_ENUM is returned if internalFormat, format or type are not legal.

SEE ALSO

glDrawPixels, glTexImage1D, glTexImage2D, gluBuild1DMipmaps,
gluErrorString, gluScaleImage
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