Generate each mip level of a texture from the previous level with a wider, smooth filter,
approximating a Gaussian blur. Sampling the small mip levels of such a texture to blur it, for
example in the reflection of a rough surface, avoids the blocks and the flickering of the box
filter. Generating the mip levels is more expensive than with MIPMAPFILTER_BOX.
Generate each mip level of a texture from the previous level with a wider, smooth filter, approximating a Gaussian blur. Sampling the small mip levels of such a texture to blur it, for example in the reflection of a rough surface, avoids the blocks and the flickering of the box filter. Generating the mip levels is more expensive than with MIPMAPFILTER_BOX.