OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Explicit Level of Detail

Normally, when using mipmaps, OpenGL will calculate the level of detail and the resulting mipmap levels from which to sample for you (see “Calculating the Mipmap Level” on Page 338 for more details on how OpenGL calculates mipmap levels). However, it is possible to override this calculation and specify the level of detail explicitly as an argument to the texture fetch function. The textureLod function takes this lod parameter in place of the bias parameter that would normally be optionally supplied to the texture function. Like other texture functions supported by GLSL, textureLod has many overloaded prototypes for the various types and dimensionalities of the supported sampler types. Some key prototypes of textureLod ...