FanType: Intention-Inferring Fan-Shaped Thumb Interface for Text Entry on Small XR Keyboards

In this paper, we present FanType, a text entry technique that enables efficient typing on small virtual keyboards in extended reality (XR), closely resembling thumb-based typing on smartphones and tablets. While virtual environments theoretically provide unlimited space, practical XR usage often occurs in mobile and spatially constrained contexts, such as when using augmented reality (AR) headsets while walking or in confined environments, where large virtual keyboards are impractical, as they occupy substantial visual space and interfere with other virtual or real content. To address this, FanType integrates a fan-shaped interface that groups keys within the thumb's reach and leverages a lift-up gesture for disambiguation, thereby reducing hand movement while preserving natural typing speed. Additionally, an intention-inferring mechanism involving tailored algorithms is implemented to counterbalance touch bias and further ensure input accuracy. A user study with 22 participants evaluated the method on tablet- and smartphone-size portrait keyboards, comparing it with a baseline (touch-only) and a state-of-the-art mid-air technique. Results provide insights into the performance of such a design and highlight the challenges of designing typing methods for small virtual keyboards.