Rulebook: An Architectural Pattern for Self-Amending Mechanics in Digital Games

Mechanics are one of the pillars of gameplay, enabled by the underlying implementation of the game and subject to constant changes during development. In particular, self-amending mechanics adjust themselves dynamically and are a common source of coupled code. The Rulebook is an architectural pattern that generalizes how developers prevent coupled code in self-amending mechanics, based on a careful research process including a systematic literature review, semistructured interviews with professional developers, and quasi-experiments. The pattern codifies changes to the game state as “effect” objects, which it matches against a dynamic pool of rules. Each rule may amend, resolve, or chain effects. By preventing the control flow of the game from becoming coupled to the specific interactions of mechanics while also promoting an extensible and flexible structure for self-amendment, our solution reduces the time developers need to iterate on the design of mechanics. This article details the Rulebook pattern and presents a case study demonstrating its design process in three different implementations of open-source jam games. Together with the typification of self-amending mechanics, this article formalizes a novel, state-of-the-art toolset for architecting games.