ACM UIST’98 pp.39-48 Popup Vernier: a Tool for Sub-pixel-pitch Dragging with Smooth Mode Transition

Dragging is one of the most useful and popular techniques in direct manipulation graphical user interfaces. However, dragging has inherent restrictions caused by pixel resolution of a display. Although in some situations the restriction could be negligible, certain kinds of applications, e.g., real world applications where the range of adjustable parameters vastly exceed the screen resolution, require sub-pixel-pitch dragging. We propose a sub-pixel-pitch dragging tool, popup vernier, plus a methodology to transfer smoothly into ‘vernier mode’ during dragging. A popup vernier consists of locally zoomed grids and vernier scales displayed around them. Verniers provide intuitive manipulation and feedback of fine grain dragging, in that pixel-pitch movements of the grids represent sub-pixel-pitch movements of a dragged object, and the vernier scales show the object’s position at a sub-pixel accuracy. The effectiveness of our technique is verified with a proposed evaluation measure that captures the smoothness of transition from standard mode to vernier mode, based on the Fitts’ law.