METHOD AND APPARATUS FOR MAINTAINING LINKS BETWEEN GRAPHIC OBJECTS IN A FREE-FORM GRAPHICS DISPLAY SYSTEM

In a computer controlled display system capable of supporting free form graphical input, techniques for maintaining the topology of a node-link structure when nodes are moved. When a node is moved, arbitrarily shaped links to other nodes will automatically be reshaped. The manner in which the link reshapes will depend on where a node is moved relative to the node to which it is linked. Various techniques for reshaping the node in order to retain the node-link structure topology are provided. A link may be reshaped by curve transformation or flipping the link shape about an axis. Curve transformation is a technique wherein the shape characteristics of a link are retained no matter where the node is moved. However, links that intersect, i.e. pass through, the nodes may arise from such reshaping. Various techniques for correcting link intersection situations and include flipping the attachment points of the links on the nodes, truncating and reattaching the link at the point where a link intersects a node or rerouting the link so that intersection is avoided.