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.