Spelunky (Boss Fight Books Book 11)

by Derek Yu

In the ATTACK state, the shopkeeper is fairly adept at finding the player, although the underlying AI is nothing special. Pathfinding is an area with a lot of research behind it and there are a variety of algorithms that people use to get a non-player character (NPC) from one place to another. For the shopkeeper, however, my simple solutions worked just fine. His ATTACK AI can be summed up like this: Every now and then, turn toward the player. Every now and then, fire my shotgun at the player if they are close enough and I have the shotgun. If the player is below me, and not too far away from me horizontally, do nothing. Otherwise, if there’s an obstacle directly in front of me, jump. Otherwise, if the player is above me, jump. Basically, when the player is at the same height or above the shopkeeper, or far enough away from him to the left or right, he likes to jump… a lot. The strength of his jump is random, too. I wasn’t sure how this would work when I first coded it, but it turns out that jumping around a lot at random heights is an effective method of getting around obstacles and finding little gaps in the wall to get through. The repeated jumping also makes his movements seem manic and unpredictable, increasing his danger factor and going hand-in-hand with his angry and violent persona. It’s a great example of how thematic imagery can mask simple mechanics.