Effects of Spatial Constraint on Bare-Hand Logographic Character Handwriting Performance in Virtual Reality

Spatial constraints significantly influence motor performance in virtual reality (VR), as interactions often involve hands hovering in mid-air. Yet their specific impact on logographic handwriting, such as Chinese and similar characters, remains underexplored. While VR text entry research is predominantly alphabetic-centric, especially English, handwriting support for complex scripts is fragmented across systems that treat physical or virtual guidance as implementation details rather than analytical or design variables. To address this, we compare three spatial constraint forms under a unified input pipeline: Unconstrained Mid-Air, Virtual Collision Surfaces, and Anchored Physical Surfaces. In a 3×3 within-subjects study (N = 24) with users writing Chinese characters of various complexity, we identified a critical stability-efficiency trade-off. While constrained conditions (virtual and physical) reduced trajectory length and rewrite counts, they increased normalized writing and total input time compared to mid-air input. Subjectively, U-MAH was rated as the most usable. Compared with HVS, HAVS reduced physical and temporal demand while still producing shorter trajectories and fewer rewrites than U-MAH. We also contribute design implications on when freer mid-air input may be preferable and when planar or physically supported writing may be more beneficial in VR handwriting.