Abstract: Dynamic computer graphics is best represented as several processes operating in parallel. Full parallel processing, however, entails much complex mechanism making it difficult to write simple, intuitive programs for generating computer animation. What is presented in this paper is a simple means of attaining the appearance of parallelism and the ability to program the graphics in a conceptually parallel fashion without the complexity of a more general parallel mechanism. Each entity on the display screen can be independently programmed to move, turn, change size, color or shape and to interact with other entities.The scheme presented herein begins with the notion of a quantum of time, or tick, within which there are no ordering constraints on events. Each entity or actor decides what it must do upon the next tick. Ticks are a powerful means of controlling parallel processes but are usually at too low a conceptual level for user convenience. Higher-level operations built upon the tick mechanism are presented, most notably the ability to instruct any entity or group of entities to gradually change or move at a rate that is itself changeable by the same operation. To illustrate these ideas a simple celestial mechanics simulation is presented. Upon each tick the velocities and positions of the objects are updated by the gravitational and propulsive forces acting upon them.Ticks are only one product of an object-oriented programming style. For the best control and the most modularity, graphics programming should be object oriented. Each object displayed, and its parts, should be independently programable. Instead of being passive data, objects should be responsible for the changes in their position or appearance. Instead of a global controller, each object should interact with the others.

Abstract: In 1973, at a cell kinetics workshop in Newcastle, Dr G. Zajicek showed a brief sequence of 8 mm film to demonstrate the progression of cells dividing from a basal layer. The film was taken from a computer visual display and the cells were represented by single letters or numbers. His film suggested that computer animation techniques might be used to study patterns of cell division and differentiation in growth cartilage. Recently the development of the DIMFILM computer graphics facility at the University of London Computer Centre made the project attractively simple to carry out. Study of the cell kinetics of growth cartilage has been based on a column by column analysis of the cells in the epiphysial plate-the analysis being performed as if each column was a completely independent unit. Using data collected in this way the GROBONE programme (Kember, 1969) was written to simulate the sequence of events-cell division, differentiation, maturation and hypertrophy-in single columns. The cell cycle times were selected at random from a distribution measured during studies of the growth plate in the rat tibia (Walker 8c Kember, 1972). The output was either numerical or in the form of a line printer graph. When the computer animated film of the growth plate was planned, the main aim, apart from the fun of doing it, was to look at column-column interactions. In the film a small section of a growth plate is represented by three rows of elliptical ‘cells’ (Fig. 1) and the GROBONE programme has been modified to grow three cell columns in parallel. Each of the thirty to thirty-six ellipses per frame was drawn by the DIMFILM package on the command CALL ELLIPSE (X, Y , A, B, 8, where the values of the coordinates X, Y for the centre of the ellipse, of the semi-axes A and B and of the angle of orientation, 0, were provided by the master GROBONE programme. When each frame was complete GROBONE advanced the growth process by a suitable time interval (5-10 min of rat standard time) so that a fresh series of parameters were available to draw the ellipses in the next frame of the film. Four types of sequence were programmed, each running 1000 to 2000 frames. They were: (1) a close up of one ‘cell’ dividing; (2) a view of the three columns of dividing and differentiating cells with the ‘top’ cells of the column fixed in position at the left of the frame; (3) a shot of the three columns with the hypertrophied cells fixed at the right so that growth occurred as the ‘top’ cells were displaced to the left; (4) a sequence as in (2) above but with each cell labelled with its generation number from an originating division of a ‘top’ cell. In this way families of cells could be followed through the plate and the relative movement of cells in

Abstract: A program has been written which enables two dimensional visualization of leg movements on a computer graphics display. Hip, knee, ankle angle, and pelvic displacement information can be input and processed to obtain Fourier coefficients characterizing these motions. The thigh, shank and foot are then displayed at, for example, two hundred points within each walking cycle, at natural speed or as slowly as desired.

Abstract: Digital and ,analog computers are being used more and more for producing various kinds of art. John Halas has collected in his book Computer Animation [1] a number of articles by computer experts that describe computer programs of potential assistance to artists who are concerned with animation and graphic artwork but who are not prepared to cope with problems requiring recourse to mathematics. The book provides a large amount of technical information, which is presented clearly. Ample diagrams are given to aid in the description of hardware and software, and a helpful glossary of technical terms is appended. Two basic approaches are considered for making graphic artworks and animated films. In one, the artistic input is in the form of a computer program. Several contributors describe modified computer languages for producing software more suitable for the purpose. Artists do not need to know how to program; they need only to apply a number of simple formulas to call into service the languages stored in the computer as a set of subroutines that comprise the 'software package'. The hardware in most of the cases considered is a microfilm recorder that receives digital information, converts it and records it as images on the film. Some detailed descriptions of such methods are presented in several articles that tend to complement each other. D. D. Weiner and S.E. Anderson present four computer programs, and outline their utility in producing 10-100 film frames in response to only a few commands. F. R. A. Hopgood and D. Ralphs analyze in detail the structure of two of these programs. Kenneth C. Knowlton and W. H. Huggins describe a particular computer language for cinema called 'EXPLOR' that enables the production of certain pictorial and textural effects, and Lillian Schwartz reports on her application of Knowlton's systems for generating images in films. Articles by Maurice Russoff and Frank E. Taylor, Robert Barfield and John V. Oldfield, Tony Pritchett, and Judah Schwartz and Edwin Taylor point out the advantages of using a computer animation technique for making educational films for mathematics or physics teaching and the opportunities that animation offer as an education aid in general. Paul Nelson describes how the effects of zoom, pan, wipe, scissoring, masking, etc. are produced with the technique. In the second basic approach through what is called an interactive system, an artist traces lines on a tablet with an electronic pen and the images of the lines appear on a screen as they are being traced. Corrections and changes can be made while the image is still on the screen or after

Abstract: In the last few years several systems have been written for aiding in the conventional two-dimensional animation process. The main purpose of these systems has been to let the computer produce missing drawings based on extreme drawings produced by animators. While there has been some success and a great deal of optimism, the promise of higher output and quality using a computer has not been realized. The transition from simple drawings optimized for use on the computer to the complicated and detailed drawings of quality conventional animation has been much harder than expected. The principle difficulty is that the animators drawings are really two dimensional projections of three dimensional characters as visualized in the animators head, hence information is lost, ie. one leg obscures another. The problem of making a program infer the original object from its projections is akin to extremely difficult artificial intelligence problems. Efforts to overcome this by drawing skeletons or increasing the number of overlays require more manual intervention thereby offsetting the gains of using the computer. One way to analyze an approach is to determine the average time required of an artist or operator at all stages of animation for every frame. A second problem not generally recognized is that a production animation system requires the management of hundreds of thousands of drawings, hence data base management techniques not normally found in experimental animation systems.