VISUALISING A SIMULATION USING ANIMATED PICTURES

Abstract

We examine an application of Jaggies, a 2D graphics system designed as part of the Jade software prototyping environment. The Jade research project is aimed at building an environment which comfortably supports the design, construction, and testing of distributed computer systems. Jaggies is based on a hierarchical data structure and avoids storage of large picture files. In this application, Jaggies provides versatile support for the graphical display of the state of the Andes simulation interpreter. Jaggies pictures are represented as linked lists of objects. An object describes an instance of a picture or a primitive. The Jaggies data structure is accessed via a set of procedures which may be called from an application program. Some of the more unusual features of Jaggies are: the system maintains an internal model of the display which may be altered incrementally; the system may be distributed across several processors; and recursively structured pictures may be defined. In Andes a simulation running on a host machine communicates with one or more Jaggies programs running on a Jade graphics workstation using Jade Inter Process Communication (JIPC). The user first goes through a design phase in which graphical icons are defined to represent specific entities in the simulation. These icons are represented in a compact form as a Jaggies data structure which resides on the workstation. Simple real-time animation functions may also be specified. As the simulation progresses the icons appear when entities are created and move in accordance with commands from the simulation program. The user may interact with the graphics; for example, different views may be created and areas of interest may be re-scaled to show details. Andes is being implemented on a VAX/780 host machine and a Corvus Concept workstation.