gluBuild3DMipmaps

gluBuild3DMipmaps: man2/gluBuild3DMipmaps.xml

gluBuild3DMipmaps builds a series of prefiltered three-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, height and depth of data are checked to see if they are a power of 2. If not, a copy of data is made and scaled up or down to the nearest power of 2. (If width, height, or depth 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, height is 23, and depth is 24, then a copy of data will scale up to 64 in width, down to 16 in height, and up to 32 in depth before mipmapping takes place. Then, proxy textures (see glTexImage3D ) are used to determine if the implementation can fit the requested texture. If not, all three dimensions are continually halved until it fits. Next, a series of mipmap levels is built by decimating a copy of data in half along all three dimensions until size 1 × 1 × 1 is reached. At each level, each texel in the halved mipmap level is an average of the corresponding eight texels in the larger mipmap level. (If exactly one of the dimensions is 1, four texels are averaged. If exactly two of the dimensions are 1, two texels are averaged.) glTexImage3D is called to load each of these mipmap levels. Level 0 is a copy of data. The highest level is log 2 ⁡ max ⁡ width height depth. For example, if width is 64, height is 16, and depth is 32, and the implementation can store a texture of this size, the following mipmap levels are built: 64 × 16 × 32, 32 × 8 × 16, 16 × 4 × 8, 8 × 2 × 4, 4 × 1 × 2, 2 × 1 × 1, and 1 × 1 × 1. These correspond to levels 0 through 6, respectively. See the glTexImage1D reference page for a description of the acceptable values for format parameter. See the glDrawPixels reference page for a description of the acceptable values for type parameter.

Note that there is no direct way of querying the maximum level. This can be derived indirectly via glGetTexLevelParameter. First, query the width, height, and depth actually used at level 0. (The width, height, and depth may not be equal to width, height, and depth respectively since proxy textures might have scaled them to fit the implementation.) Then the maximum level can be derived from the formula log 2 ⁡ max ⁡ width height depth. gluBuild3DMipmaps is only available if the GLU version is 1.3 or greater. Formats GLU_BGR, and GLU_BGRA, and types GLU_UNSIGNED_BYTE_3_3_2, GLU_UNSIGNED_BYTE_2_3_3_REV, GLU_UNSIGNED_SHORT_5_6_5, GLU_UNSIGNED_SHORT_5_6_5_REV, GLU_UNSIGNED_SHORT_4_4_4_4, GLU_UNSIGNED_SHORT_4_4_4_4_REV, GLU_UNSIGNED_SHORT_5_5_5_1, GLU_UNSIGNED_SHORT_1_5_5_5_REV, GLU_UNSIGNED_INT_8_8_8_8, GLU_UNSIGNED_INT_8_8_8_8_REV, GLU_UNSIGNED_INT_10_10_10_2, and GLU_UNSIGNED_INT_2_10_10_10_REV are only available if the GL version is 1.2 or greater.