gluBuild2DMipmaps

gluBuild2DMipmaps: man2/gluBuild2DMipmaps.xml

gluBuild2DMipmaps builds a series of prefiltered two-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 and height of data are checked to see if they are a power of 2. If not, a copy of data (not data ), is scaled up or down to the nearest power of 2. 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 GLU_MAX_TEXTURE_SIZE.) Next, a series of mipmap levels is built by decimating a copy of data in half along both dimensions until size 1 × 1 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 × 1 or 1 × 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 log 2 ⁡ 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: 64 × 16, 32 × 8, 16 × 4, 8 × 2, 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 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 for the width and height actually used at level 0. (The width and height may not be equal to width and height 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. 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.