Bump mapping

Jim Blinn described the idea in 1978. A bump or height map says how the surface normal should tilt at each point, and the lighting is computed against that perturbed normal — the eye reads the resulting shadow pattern as pits and bumps even though the polygon is mirror-flat.

The technique exploded in the demoscene around the turn of the century, often as "emboss" or dot3 variants run in real time before graphics cards had native support. Its successor, normal mapping, stores the whole normal vector in an RGB texture rather than a single height, sharpening the trick enough for modern games.