Snap-dragging

We are interested in the problem of making precise line drawings using interactive computer graphics. In precise line drawings, specific relationships are expected to hold between points and lines. In published interactive drawing systems, precise relationships have been achieved by using rectangular grids or by solving simultaneous equations (constraints). The availability of fast display hardware and plentiful computational power suggest that we should take another look at the ruler and compass techniques traditionally used by draftsmen. Snap-dragging uses the ruler and compass metaphor to help the user place his next point with precision, and uses heuristics to automatically place guiding lines and circles that are likely to help the user construct each shape. Snap-dragging also provides translation, rotation, and scaling operations that take advantage of the precision placement capability. We show that snap-dragging compares favorably in power and ease of use with grid or constraint techniques.