Generalized graphical object editing
Mark Linton, John M. Vlissides · 1990
Many editors use the graphics capabilities of personal workstations to provide a visual editing environment. Such editors present graphical representations of familiar objects and allow the user to manipulate the representations directly. This style of interaction is usually more intuitive to the user than typing statements in a command language. However, implementing a graphical object editor has been a difficult undertaking. Though many packages exist that aid in the construction of graphical user interfaces, none are designed specifically for building graphical object editors. This is significant because there is a substantial semantic gap between general user interfaces and the functionality of graphical object editors. For example, user interface packages usually provide buttons, scroll bars, and ways to assemble them, but they do not offer primitives for building drawing editors that produce PostScript or schematic capture systems that produce netlists. Higher-level abstractions are needed to make such applications easier to develop. Unidraw is a framework for creating object-oriented graphical editors in domains such as technical and artistic drawing, music composition, and circuit design. The Unidraw architecture simplifies the construction of these editors by providing programming abstractions that are common across domains. Unidraw defines four basic abstractions: components encapsulate the appearance and semantics of objects in a domain, tools support direct manipulation of components, commands define operations on components and other objects, and external representations define the mapping between components and the file format generated by the editor. Unidraw also supports multiple views, graphical connectivity and confinement, and dataflow between components. This thesis describes the Unidraw design, implementation issues, and three experimental domain-specific editors we have developed with Unidraw: a drawing editor, a user interface builder, and a schematic capture system. Our results indicate a substantial reduction in implementation time and effort compared with existing tools.