3D modelling and printing are becoming increasingly popular. However, beginners often face high barriers of entry when trying to use existing 3D modelling tools, even for creating simple objects. This is further complicated on mobile devices by the lack of direct manipulation in the Z dimension. In this paper, we explore the possibility of using foldable mobile devices for modelling simple objects by constructing a 2.5D display and interaction space with folded touch screens. We present a set of novel interaction techniques - AngleCAD, which allows users to view and navigate a 3D space through folded screens, and to modify the 3D object using the physical support of touchscreens and folding angles. The design of these techniques was inspired by woodworking practices to support surface-based operations that allow users to cut, snap and taper objects directly with the touch screen, and extrude and drill them according to the physical fold angle. A preliminary study identified the benefits of this approach and the key design factors that affect the user experience.
Foldable screens are gaining popularity on mobile platforms as it features novel design schemes for view management and screen extension. However, challenges for performing touch input arises when it is folded in various angles and held in various ways. This paper is among the first to systematically evaluate how touch gestures perform under the influence of various fold angles and holding postures. Three gestures for moving objects on touch screens, namely Direct Drag, Hold & Tap, and Throw & Catch, were adopted from previous works and compared in a controlled experiment, where five fold angles and portrait vs landscape modes were varied. Results provide an in-depth understanding of how orientation, fold angle, target distance and direction affects the performance of each technique. Overall Direct Drag was the most accurate but highly inefficient and tiring. Hold & Tap was the most efficient technique with comparable accuracy, except being much more error-prone in Landscape than Portrait. Throw & Catch had a more balanced trade-off between efficiency and accuracy.
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