Stylus input and editing without prior selection of mode

This paper offers a solution to the mode problem in computer sketch/notetaking programs. Conventionally, the user must specify the intended "draw" or "command" mode prior to performing a stroke. This necessity has proven to be a barrier to the usability of pen/stylus systems. We offer a novel Inferred-Mode interaction protocol that avoids the mode hassles of conventional sketch systems. The system infers the user's intent, if possible, from the properties of the pen trajectory and the context of the trajectory. If the intent is ambiguous, the user is offered a choice mediator in the form of a pop-up button. To maximize the fluidity of drawing, the user is entitled to ignore the mediator and continue drawing. We present decision logic for the inferred mode protocol, and discuss subtleties learned in the course of its development. We also present results of initial user trials validating the usability of this interaction design.