The message is the medium: Multiprocess structuring of an interactive paint program

Abstract

An innovative design for an interactive paint program has been developed based on multiple processes and message passing. Traditional paint programs combine interrupt-driven support of a graphical input device, such as a mouse or tablet, with the coloring of pixels in a raster display. We advocate a different design methodology which is illustrated in our implementation. The multiple processes and message passing primitives provided by some real-time operating systems encourage the design of parallel-program architectures and anthropomorphic programming structures, analogous to artist procedures and the metaphors of Smalltalk. The Thoth operating system was used to experiment with such an anthropomorphic design. Thoth provides a hospitable environment in which to investigate the distribution of algorithms between software and microprogrammed hardware processes, the performance and responsiveness of a multiple-process interactive program, and experimental user interfaces using an Ikonas 3000 frame buffer. The paint program consists of processes which handle the graphics tablet, track an iconic cursor, paint a selection of brushes, fill regions of the image, draw lines, and implement the user interface. Some processes have been implemented both in software and microcode.