+,+ ompete+ Carla's Island Revisited Nelson L. Max Lawrence Liverrnore National Laboratory, P.O. Box 808, Livermore, CA 94550, USA A computer animated movie, titled "Carla's Island", showing sunset and moonset over the ocean, was recreated as an inter- active art installation. The movie "Carla's Island" was produced by ray-tracing on the Cray-1 as described in Max (1981). Figure la-c are single frames from this movie, showing the same ocean scene at different times of day. The terrain and clouds are the same in all three views. The only changes are a) the positions of the waves, b) the col- ors, and c) the position of the sun or moon. In making the movie, a cycle of 144 ray-traced images was stored on three magnetic tapes. The wave motion was made periodic so that the last frame could be fol- lowed again by the first. Each pixel was assigned one of 256 numbers, depending on where the direct or reflected ray hit the sky, clouds, hills, cliffs, or beach. As the film was being recorded, a minicomputer gradually changed the tables which assigned these 256 numbers to their colors ac- cording to the time of day, and added in the sun or the moon be- hind the clouds or hills. This mini- computer was thus able to cycle through the 144 frames automati- cally, doing simple computations to enhance a limited number of supercomputer-produced frames. During my presentation at SIG- GRAPH '81, I proposed that these simple computations could also be done on a raster graphics workstation. When Apollo Com- puter, Inc. planned to announce their color DN660 at SIG- GRAPH '82, they requested the data for one frame of my movie to use in a" slide show" presenta- tion on their machine. I instead suggested that we could make a real-time demonstration and was invited to spend the week before the meeting preparing it. It turned out that the DN 660 had exactly the capabilities necessary to compute the changes a), b) and c) very efficiently. First of all, it had two megabytes of graphics memory connected with special high speed block transfer hardware ("bitblit"). This memory was enough to hold two full frames of a 512 x 512 im- Fig. 1 a Islands, ocean, and clouds in the afternoon, The Visual Computer (1986) 2:171-173 9 Springer-Verlag 1986 b Scene of Fig. i at sunset, e Scene of Fig. 1 at moonset 171