HiPad: Text entry for Head-Mounted Displays Using Circular Touchpad

Text entry in virtual reality (VR) is currently a common activity and a challenging problem. In this paper, we introduce HiPad, leveraging a circular touchpad with a circular virtual keyboard, to support the one-hand text entry in mobile head-mounted displays (HMDs). The design of HiPad's layout is based on a circle and a square with rounded corners, where the outer circle is subdivided into six keys' regions containing letters. This technique input text by a common hand-held controller with a circular touchpad for HMDs and disambiguates the word based on the sequence of keys pressed by the user. In our first study, three potential layouts are considered and evaluated, leading to the design containing six keys. By analyzing the touch behavior of users, we optimize the 6-keys layout and conduct the second study, showing that the optimized layout has better performance. Then the third study is conducted to evaluate the performance of 6-keys HiPad with VE-layout and TP-layout and to study the learning curves. The results show that novices can achieve 13.57 Words per Minute (WPM) with VE-layout and 11.60 WPM with TP-layout and the speeds increase by 74.42% for VE-layout users and by 81.53% for TP-layout users through a short 60-phrase training.