Culling objects that are behind objects?

[Fezziwig]

Is there a name for culling objects that are hidden by other objects? And how is it done?

[cireneikual]

Occlusion culling. The easiest way is to use the extension GL_ARB_occlusion_query. With this, you render your scene front to back. You group objects into bounding volumes, and before rendering the objects, you render the bounding volume while an occlusion query is active. It then counts the number of fragments that passed the depth test. If this amount is 0, it is occluded.