Stunningly realistic video game visuals made by simulating light rays

"Oh, that looks gorgeous," drawls an onlooker in a Texas accent, as I guide my fighter through a gloomy, broken-down shack in a video game called Metro Exodus. I'm struggling in hand-to-hand combat with a zombie, so Dmitry Zhdan, who worked on the game, grabs the controls and beats my foe to death with a rifle butt.