GoThrough: A tool to render and interact with arbitrary planar transformative portals

Portals are commonly used in video games (e.g., Portal and the classic Asteroids). In this work, we introduce GoThrough, a tool that enables users with little to no previous knowledge to add transformative portals to 3D scenes in the Unity game engine. GoThrough implements both the visual and physical aspects of portals, leaving room for other extensions by the user. We introduce an approach for portals to work robustly in terms of geometry and rendering and explore common pitfalls (and how to handle them). Lastly, we put in evidence several portal-based mechanics and implement use cases to demonstrate them. The tool is shown to work in various example scenarios and has been evaluated quantitatively for performance, performing in real-time in various scenarios. We conducted user tests to analyse GoThrough qualitatively and an experiment of experts to understand how the tool hinders or empowers their expressiveness. With a SUS score of 87.5, we concluded that GoThrough is intuitive enough to be used by non-experts, making the process of creating impossible 3D worlds much less cumbersome. At last, experts were able to conceive unanticipated mechanics and revealed that the tool allowed prototypes that would not be developed in a feasible time otherwise.