Hierarchical Semantic Wave Function Collapse

Abstract

Virtual worlds are rapidly increasing in size, enabled by advancements in computing technology, which puts a large burden on designers creating them.
Procedural Content Generation can help alleviate this burden, though lacks precise control, to the detriment of designer intent. Some PCG algorithms, such as Wave Function Collapse (WFC), known for generating tile-based content adhering to certain constraints, are able to induce this control through mixed-initiative editing opportunities, combining the efforts of humans and machines while capturing designer intent. However, stock WFC operates on a flat set of tiles with all their semantics blurred together, which unnecessarily strains designers with additional cognitive load when working with such detailed tiles.



We therefore propose Hierarchical Semantic Wave Function Collapse (HSWFC), a generalized approach to WFC that augments the tileset with a new type of tile, the meta-tile, which represents semantic traits, and then organizes the tileset into a hierarchy akin to a taxonomy induced by such semantic representations: the meta-tree. A cell once collapsed to any tile high up in the meta-tree (such as "forest" or "village"), can further collapse to concrete tiles at the bottom (such as “tree” or “wall”).


We investigate how this extension in data organization affects the original algorithm, and explore several novel editing facilities, including e.g. sketching with semantic tiles, controlling tile distributions, regenerating areas that represent specific semantics, and more. A prototypical HSWFC-driven tile-editor was developed and evaluated through a user study, confirming that such an editor indeed reduces cognitive load compared to its stock WFC counterpart, and that the newly enabled features are highly valued by environment designers.