GLUBUILD1DMIPMAPS

Section: Misc. Reference Manual Pages (3G)
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NAME

gluBuild1DMipmaps - builds a one-dimensional mipmap

C SPECIFICATION

GLint gluBuild1DMipmaps( GLenum target,


                           GLint internalFormat,
                           GLsizei width,
                           GLenum format,
                           GLenum type,
                           const void *data )

delim $$

PARAMETERS

target: Specifies the target texture. Must be GL_TEXTURE_1D.
internalFormat: Requests the internal storage of the texture image. The most current version of the SGI implementation of GLU does not check this value for validity before passing it on to the underlying OpenGL implementation. A value that is not accepted by the OpenGL implementation will lead to an OpenGL error. The benefit of not checking this value at the GLU level is that OpenGL extensions can add new internal texture formats without requiring a revision of the GLU implementation. Older implementations of GLU check this value and raise a GLU error if it is not 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 of the pixel data. Must be one of GL_COLOR_INDEX, GL_DEPTH_COMPONENT, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_BGR, GL_BGRA, GL_LUMINANCE, 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, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, or GL_UNSIGNED_INT_2_10_10_10_REV.
data: Specifies a pointer to the image data in memory.

DESCRIPTION

gluBuild1DMipmaps builds a series of prefiltered one-dimensional texture maps of decreasing resolutions called a mipmap. This is used for the antialiasing of texture mapped primitives.

A return value of zero 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 2. If not, a copy of data is scaled up or down to the nearest power of 2. (If width is exactly between powers of 2, then the copy of data will scale upwards.) This copy will be used for subsequent mipmapping operations described below. 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 $1 ~times~ 1$ 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 ${log sub 2}(width)$. For example, if width is 64 and the implementation can store a texture of this size, the following mipmap levels are built: $64 ~times~ 1$, $32 ~times~ 1$, $16 ~times~ 1$, $8 ~times~ 1$, $4 ~times~ 1$, $2 ~times~ 1$ and $1 ~times~ 1$. These correspond to levels 0 through 6, respectively.

See the glTexImage1D reference page for a description of the acceptable values for the type parameter. See the glDrawPixels reference page for a description of the acceptable values for the data parameter.

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 ${log sub 2}(width)$.

Formats GL_BGR, and GL_BGRA, and types GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, and GL_UNSIGNED_INT_2_10_10_10_REV are only available if the GL version is 1.2 or greater, and if the GLU version is 1.3 or greater.

ERRORS

GLU_INVALID_VALUE is returned if width is < 1.

GLU_INVALID_ENUM is returned if format or type are not legal.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_BYTE_3_3_2 or GL_UNSIGNED_BYTE_2_3_3_REV and format is not GL_RGB.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_6_5 or GL_UNSIGNED_SHORT_5_6_5_REV and format is not GL_RGB.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_4_4_4_4 or GL_UNSIGNED_SHORT_4_4_4_4_REV and format is neither GL_RGBA nor GL_BGRA.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_5_5_1 or GL_UNSIGNED_SHORT_1_5_5_5_REV and format is neither GL_RGBA nor GL_BGRA.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_INT_8_8_8_8 or GL_UNSIGNED_INT_8_8_8_8_REV and format is neither GL_RGBA nor GL_BGRA.

GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_INT_10_10_10_2 or GL_UNSIGNED_INT_2_10_10_10_REV and format is neither GL_RGBA nor GL_BGRA.