cfry@watdcsu.waterloo.edu (C.Fry - Inst. Computer Research) (09/27/88)
Snap-Dragging: Interactive Geometric Design in Two and Three Dimensions by Dr. Eric Bier of Xerox PARC Palo Alto, CA Abstract Snap-dragging is an interactive technique for precisely placing shapes in a two- or three-dimensional drawing space. It combines three sub-techniques: a general purpose ``gravity'' function that allows a software cursor to be snapped to shapes and their inter- sections, a set of alignment objects used much like the lines and circles of traditional ruler and compass construction, and smooth motion affine transformations, such as translation, rotation, and scaling, that take advantage of gravity and alignments to achieve precise positioning. Snap-dragging is a compromise between power and ease of use. While nearly as easy to use as systems with gravity-active rec- tangular grids, it facilitates the construction of a larger class of shapes. While it does not permit the user to describe objects that change in time, as constraint-based systems do, it allows a large class of static shapes to be defined very rapidly. In par- ticular, there is no need to ``debug'' a constraint network. The user interface works nearly identically in two or three di- mensions. In three dimensions, snap-dragging works in a single perspective view, with a two-dimensional pointing device. Video- tapes demonstrating snap-dragging in action will be shown. DATE: Wednesday, October 5, 1988 TIME: 3:30 p.m. PLACE: University of Waterloo, Davis Centre, Room 1302 Everyone is welcome. Refreshments served.