HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 37

B gluBuild1DMipmaps Next, gluBuild1DMipmaps builds a series of mipmap levels; it halves a copy of data (or a scaled version of data, if necessary) until size 1 is reached. At each level, each texel in the halved image is an average of the corresponding two texels in the larger image. glTexImage1D is called to load each of these images by level. If width is a power of 2 which fits in the implementation, level 0 is a copy of data, and the highest level is log2 width. For example, if width is 64, the following images are built: 64x1, 32x1, 16x1, 8x1, 4x1, 2x1 and 1x1. These correspond to levels 0 through 6, respectively. See the glTexImage1D reference page for a description of the acceptable values for type. See the glDrawPixels reference page for a description of the acceptable values for data. Notes While you can't query the maximum level directly, you can derive it indirectly by calling glGetTexLevelParameter. First, query for the width actually used at level 0. (The width may be unequal to width since gluBuild1DMipmaps might have shrunk or expanded width if width isn't a power of 2 or if the implementation only supports smaller textures. The maximum level can then be derived using the formula log2 width. Errors • GLU_INVALID_VALUE is returned if width is negative. • GLU_INVALID_ENUM is returned if format or type is not one of the accepted values. Bugs Passing GL_STENCIL_INDEX or GL_DEPTH_COMPONENT as format will incorrectly return 0 and set the error code to GL_INVALID_ENUM. It should return GLU_INVALID_ENUM and not set an error code. See Also glTexImage1D, gluBuild2DMipmaps, gluErrorString, gluScaleImage Chapter 2 37