Literally Unplayable: On Constraint-Based Generation of Uncompletable Levels

Most research in procedural content generation has, understandably, focused on generating levels that are completable-that is, levels where it is possible for a player to complete them. In this work we explore the generation of uncompletable levels and their applications. Building on an existing constraint-based level generator, we add support for constraints that a level's goal is not reachable from its start. The generator can thus create levels that are similar to completeable levels in many ways (such as local tile patterns), yet are not possible to complete. We then describe several applications of those constraints and the resulting levels, including: qualitatively characterizing what makes levels uncompletable; creating training data for completability classifiers; checking that a generator can only generate completable levels; and generating levels that require the player to use a special move.