Left 4 Dead
Left 4 Dead uses the latest version of Valve's Source engine, with improvements such as multi-core processor support and physics-based animation to more realistically portray hair and clothing, and to improve physics interaction with enemies when shot or shoved in different body parts. Animation was also improved to allow characters to lean realistically when moving in curved paths.
Rendering and artificial intelligence were scaled up to allow for greater number of enemies who can navigate the world in better ways, such as climbing, jumping or breaking obstacles. Lighting has been enhanced with new self-shadowing normal mapping and advanced shadow rendering that is important to convey information about the environment and player actions.
HD 4850: Here we see no real change.
HD 4870 X2: Here we see no real change.
HD 4890: Here we see no real change.