Implement automatic MIPMAP generation from OpenGL
1.4 specification/SGI extension.
Setting the texture parameter GENERATE MIPMAP to
TRUE introduces a side effect
to any modification of the levelbase of a mipmap array,
wherein all higher levels of
the mipmap pyramid are recomputed automatically by
successive filtering of the
base level array.
Automatic mipmap generation was promoted from the
SGIS generate mipmap extension.