“The message is the medium: Multiprocess structuring of an interactive paint program” by Beach, Beatty, Booth, Plebon and Fiume

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.

1. Beach, R.J., Beatty, J.C., Booth, K.S., White, A.R., “Documentation Graphics at the University of Waterloo,” International Conference on Research and Trends in Document Preparation Systems, Swiss Institute of Technology, Lausanne, 1981.
2. Beatty, J.C., Booth, K.S., Matthies, L.H., “Watkins Algorithm Revisited,” CMCCS, Waterloo, 1981.
3. Booth, K.S., and Gentleman, W.M., “Anthropomorphic Programming,” Conference on Issues for Large Scale Computing, Salishan Lodge, Oregon, March 1982.
4. Booth, K.S., and MacKay, S.A., “Techniques for Frame Buffer Animation,” Graphics Interface ’82 Conference Proceedings, Toronto, 1982.
5. Cargill, T.A., “A View of Source Text for Diversely Configurable Software,” PhD thesis, University of Waterloo, 1979.
6. Cheriton, D.R., “Multi-process Structuring and the Thoth Operating System,” PhD thesis, University of Waterloo, 1979.
7. Cheriton, D.R., Malcolm, M.A., Melen, L.S., and Sager, G.R., “Thoth, a Portable Real-time Operating System,” CACM, Vol 22, No 2, 1979.
8. Dyment, Doug, “A Corkscrew for the Software Bottleneck,” Micros 1:2 (October 1980) pp 21-24.
9. Evans, K.B., Tanner, P.P., and Wein, M., “Tablet Based Valuators that Provide One, Two, or Three Degrees of Freedom,” Computer Graphics, Vol 15, No 3, Aug. 1981.
10. Gentleman, W.M., “Message Passing Between Sequential Processes: the Reply Primitive and Administrator Concept,” Software-Practice and Experience, Vol 11, pp. 435-466, 1981.
11. Goldberg, A., and Ingalls, D.H.H., “The Smalltalk-80 System,” BYTE, Vol 6, No 8, Aug. 1981.
12. Gurd, R.P., “A Tiny C Compiler for a Bit-Sliced Microprocessor,” Master’s thesis, University of Waterloo (in preparation), 1982.
13. Kahn, K, and Hewitt, C., “Dynamic Graphics Using Quasi Parallelism,” Computer Graphics, Vol 12, No 3, Aug. 1978.
14. Kay, A., Goldberg, A., “Personal Dynamic Media,” Computer, IEEE, Vol 10, No 3, Mar. 1977.
15. Levoy, M., “Computer Animation Tutorial Notes,” SIGGRAPH ’81, 1981.
16. Malcolm, M.A., et al., Zed Reference Manual, Thoth Computer Research Foundation, University of Waterloo, 1980.
17. Reynolds, C.W., “Computer Animation with Scripts and Actors,” Computer Graphics, this issue.
18. Smith, A.R,, “Paint,” Tech. Memo. No. 7, Computer Graphics Lab, NYIT, Old Westbury, NY, July 1978.
19. Smith, A.R., “Tint Fill,” Computer Graphics, Vol 13, No 2, Aug. 1979.
20. Shoup, R.G., “Color Table Animation,” Computer Graphics, Vol 13, No 2, Aug. 1979.
21. Tilbrook, D.M, “A Newspaper Pagination System,” M.Sc. thesis, Department of Computer Science, University of Toronto, 1976.