S.T.A.L.K.E.R.: Clear Sky, is the stand-alone prequel for S.T.A.L.K.E.R.: Shadow of Chernobyl, a first-person shooter computer game by Ukrainian developer GSC Game World. The game consists of a roughly 50/50 mix of new areas and old, remodeled areas from the previous game. The X-ray graphics engine has been updated to version 1.5 and includes DirectX 10 support. Additionally, the AI received an overhaul to accommodate the new faction wars feature.