There’s a lot more that goes into an online video game than meets the eye. Behind the slash, bang, and pow are complex engineering and intricate design to create texture, animation, and sounds. Jason Krupat, 38, is the mastermind behind the games launched by GSN (Game Show Network), a multimedia entertainment company with offices in Waltham. Krupat dreams up the type of play that will take place, the features it will include, how the game will use the technology on a particular platform.