gluBuild1DMipmaps

gluBuild1DMipmaps: man2/gluBuild1DMipmaps.xml

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 × 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 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 × 1, 32 × 1, 16 × 1, 8 × 1, 4 × 1, 2 × 1, and 1 × 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.

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 2 ⁡ width. 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, and if the GLU version is 1.3 or greater.