  Spatial drawing using ruled-surface brush strokes is a popular mode of
content creation in immersive VR, yet little is known about the usability of
existing spatial drawing interfaces or potential improvements. We address these
questions in a three-phase study. (1) Our exploratory need-finding study (N=8)
indicates that popular spatial brushes require users to perform large wrist
motions, causing physical strain. We speculate that this is partly due to
constraining users to align their 3D controllers with their intended stroke
normal orientation. (2) We designed and implemented a new brush interface that
significantly reduces the physical effort and wrist motion involved in VR
drawing, with the additional benefit of increasing drawing accuracy. We achieve
this by relaxing the normal alignment constraints, allowing users to control
stroke rulings, and estimating normals from them instead. (3) Our comparative
evaluation of StripBrush (N=17) against the traditional brush shows that
StripBrush requires significantly less physical effort and allows users to more
accurately depict their intended shapes while offering competitive ease-of-use
and speed.
