  Behavior trees (BTs) are a popular method for modeling NPC and enemy AI
behavior and have been widely used in commercial games. In this work, rather
than use BTs to model game playing agents, we use them for modeling game design
agents, defining behaviors as content generation tasks rather than in-game
actions. Similar to how traditional BTs enable modeling behaviors in a modular
and dynamic manner, BTs for PCG enable simple subtrees for generating parts of
levels to be combined modularly to form complex trees for generating whole
levels as well as generators that can dynamically vary the generated content.
We refer to this approach as Procedural Content Generation using Behavior
Trees, or PCGBT, and demonstrate it by using BTs to model generators for Super
Mario Bros., Mega Man and Metroid levels as well as dungeon layouts and discuss
several ways in which this paradigm could be applied and extended in the
future.
