Finally got a handle on bumpmapping for 1998 #dreamcast hardware. The basic idea is to simulate realtime light-responsive surface details on relatively simple geometry by providing a 'map' image that describes how light should interact with the surfaces, as if a lot more surface detail were being drawn.
Super detailed geometry would take up more of the limited RAM and needs much more CPU time to calculate lighting and feed into the graphics pipeline every frame. This is just six faces each with four vertices, a non bumpmapped version would need a mesh with thousands of verts.
#gamedev
(edit: spelt 'game' wrong, amazing)