US Patent 7623128 Interactive constraint-based alignment objects

A computer-implemented graphics system for creating and editing interactive constraint-based alignment objects. One or more drawing entities are created in the graphics system, wherein the drawing entities are linked together as an alignment object, and one or more of the entities includes a persistent tangency rule. The drawing entities comprise lines, arcs and/or spirals, although other entities are possible. The drawing entities are then edited in the graphics system, wherein the persistent tangency rules affect the drawing entities' geometry while the drawing entities are being edited. The persistent tangency rule comprises: (1) no tangency, (2) tangency to an entity before or after, or (3) tangency to an entity before and after.