Creates 2-dimensional (2D) mipmaps.
OpenGL C bindings library: libGL.a
GLint gluBuild2DMipmaps(GLenum target, GLint internalFormat, GLsizeiwidth, GLsizei height, GLenum format, GLenum type, const void *data)
The gluBuild2DMipmaps subroutine 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 in width and down to 16 in depth, 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 subroutine for a description of the acceptable values for format parameter. See the glDrawPixels subroutine for a description of the acceptable values for type parameter.
| target | Specifies the target texture. This value must be GL_TEXTURE_2D. |
| internalFormat | Specifies the number of color components in the texture. Values must be 1, 2, 3, or 4 or one of the following symbolic constants:
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| width | Specifies the width, in pixels, of the texture image. |
| height | Specifies the height, in pixels, of the texture image. |
| format | Specifies the format of the pixel data. The following symbolic values are valid:
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| (See the glTexImage1D subroutine for acceptable values for the Format parameter.) | |
| type | Specifies the data type. The following data types are valid for data:
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| (See the glDrawPixels subroutine for acceptable values for the Type parameter.) | |
| data | Specifies a pointer to the image data in memory. |
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)).
| /usr/include/GL/gl.h | Contains C language constraints, variable type definitions, and ANSI function prototypes for OpenGL. |
The glDrawPixels subroutine, glTexImage1D subroutine, glTexImage2D subroutine, glTexImage3D subroutine, gluBuild1DMipmaps subroutine, gluBuild3DMipmaps subroutine, gluErrorString subroutine, glGetTexImage subroutine, glGetTexLevelParameter subroutine, gluBuild1DMipmapLevels subroutine, gluBuild2DMipmapLevels subroutine, gluBuild3DMipmapLevels subroutine .