Comics have a rich visual vocabulary, and people find them appealing. They are also an effective form of communication. We have built a system, called Comic Chat, that represents on-line communications in the form of comics. Comic Chat automates numerous aspects of comics generation, including balloon construction and layout, the placement and orientation of comic characters, the default selection of character gestures and expressions, the incorporation of semantic panel elements, and the choice of zoom factor for the virtual camera. This paper describes the mechanisms that Comic Chat uses to perform this automation, as well as novel aspects of the program's user interface. Comic Chat is a working program, allowing groups of people to communicate over the Internet. It has several advantages over other graphical chat programs, including the availability of a graphical history, and a dynamic graphical presentation.

Many tasks performed using computer interfaces are very repetitive. While programmers can write macros or procedures to automate these repetitive tasks, this requires special skills. Demonstrational systems make macro building accessible to all users, but most provide either no visual representation of the macro or only a textual representation. We have developed a history-based visual representation of commands in a graphical user interface. This representation supports the definition of macros by example in several novel ways. At any time, a user can open a history window, review the commands executed in a session, select operations to encapsulate into a macro, and choose objects and their attributes as arguments. The system has facilities to generalize the macro automatically, save it for future use, and edit it.

Graphical interfaces typically provide their users with little idea of a session's history, except insofar as it is reflected in the current state of the system. If undo and redo commands are provided, they are often the only way to review the actions performed, cycling through them in sequence. We introduce the notion of an editable graphical history that can allow the user to review and modify the actions performed with a graphical interface. We have designed a testbed system that creates a series of automatically-generated panels that depict in chronological order the important events in the history of a user's session with Chimera, a graphical editor. Our system uses heuristics to determine the contents of each panel and the actions that it illustrates. The user may scroll through the sequence of panels, reviewing actions at different levels of detail, and selectively undoing, modifying, and redoing previous actions.

Many graphics tasks, such as the manipulation of graphical objects, and the construction of userinterface widgets. can be facilitated by geometric constraints. However, the difficulty of specifying constraints by traditional mcthods forms a barrier to their widespread use. In order to make constraints casier to declare, \\le have developed a method of specifying constraints implicitly. through multiple examples. Snapshots are taken of an initial scene configuration. and one or more additional snapshots are taken after the scene has been cditcd into other valid configurations. The constraints that are satisfied in all the snapshots are then appl ied to the scene objects. We discuss an efficient algorithm for inferring constraints from multiple snapshots. The algorithm has been incorporated into the Chimera editor. and several examples of its use are discussed.

Graphical search is a technique for finding all instances of a graphical pattern in a synthetic picture in which objects are regions bounded by lines and curves. The pattern may descirbe shape, color and other properties. Matched objects may be allowed to differ from the pattern in rotation and scale or may differ in shape by a specified tolerance. Graphical replace is a technique for replacing the shape, color, or other properties of matched objects with new properties described in a replacement pattern. Combined, the two techniques are similar to textual search and replace in text editors. Graphical search and replace can be used to make global changes to illustrations with repetitive patterns, independent of the means used to make those patterns. It can also be used to create a class of iterative or recursive shapes that can be specified by replacement rules.