At the time, CG70 was the largest Computer Graphics conference held world-wide with 100 speakers, 40 exhibitors and over 1000 attendees.
Sherwood E Anderson, The John Hopkins University, Applied Physics Laboratory, Silver Spring, Maryland
Graphical output via the computer has been available for many years now, but generally only one device at a time has been available to produce the display, and only one mode of output or input has been considered. This paper describes the successful integration of several components to form a graphics system which produces plots, animated crt displays, and motion pictures. Two similar driving programs are employed to create either planar or 3 dimensional dynamic picture sequences from picture language commands and/or other pictorial input.
An on-line computer animation system has been set up at the Applied Physics Laboratory of The Johns Hopkins University (see fig. 1). An IBM 360/91 is used to drive a 2250/3 cathode ray tube in a time shared environment. A program user can type in picture language commands from the alphanumeric keyboard, scan and edit this code using the light pen, then call for the dynamic sequence to be displayed. On the programmed function keyboard switches are depressed to advance a selected number of frames in a movie editor mode. When a picture sequence is considered to be acceptable, a permanent record is made by one of the following 3 devices:
Two major programs were written which accept this picture language: HICAMP (Hopkins Implementation of Computer Aided Motion Pictures) and HICAMPER (Hopkins Implementation of Computer Aided Movie Perspectives). They were adapted by the author from his previous work for the E.E. Dept. at Syracuse University, and are fully described in his M.S.E.E. thesis. HICAMP produces movies of planar, 2-D objects, while HICAMPER accepts similar commands to produce movies of 3-D objects in perspectives (see fig. 2).
Both programs utilize a novel list processing concept to store pictures, which allows a selected sub-group, or an entire scene to be manipulated by a single command. Loops of instructions can generate hundreds or even thousands of frames of film, depicting complex motion of any sort, expressible by an equation. Simple motions (translation, rotation, or sizing) can occur separately or compounded together. Although the programs were written in FORTRAN for transportability to other computing centers, they are stored on disc in load module form. All instructions are read in as data cards, so that the compiler phase is unnecessary, resultinq in very efficient real time operation. Basic figures, such as a circle, rectangle, or arrow are invoked by giving an easily recalled mnemonic with the desired location and dimensions. A full alphabet, along with special characters are also provided. Since the letters are treated as pictorial data, they can be manipulated in the same manner instead of being limited to several font sizes. Any rectangular area can be masked out or windowed in automatically. These areas can be changed dynamically, creating unusual wipes or dissolves for special effects. If the first and last views of a figure are specified, all interstitial views can be calculated by a linear interpolation when called for. This technique can even be used to produce cartoon styled movies.
The dynamic sequence of images is displayed on the IBM 2250 crt. The viewing area of this tube is a twelve inch square, but programming logic truncates all lines to a vertical height of nine inches. This allows a picture rectangle with a 3 to 4 height to width ratio, which complies with the border frame for 16 mm. film. The display thus has the advantage of simulating a movie editor, and the convenient 9 × 12 inch viewing area allows co-ordinates to be measured directly from the tube face if necessary.
The progranuned function keyboard (an array of 32 push buttons) is used to control the action of the display. Several buttons allow a fixed number of frames to advance: l (single cycle), 6, 24, 96, or 9999 (essentially free run). Two other buttons specify the projection speed: either 10 or 20 frames per second. Finally, the light pen can be used to abort the program if necessary.
Alterations or additions to the picture language instructions can be readily made by the programmer without leaving the graphics terminal. The set of cards are initially keypunched and loaded onto a direct access device (disc). The IBM provided Data Set Edit program was implemented to provide interactive command updating. This program allows a data set to be scrolled through and displays 20 card images at a time on the crt screen. Any card may be selected by means of the light pen, and edited in any part by means of the alphanumeric keyboard. New commands may likewise be entered into a key-in area, and inserted after any existing card in the sequence. Once the data set has been amended, it may be rerun and checked once again for errors or additions.
To expedite the input process of complex or irregular diagrams, a Pencil Follower Coordinate Digitizer is used offline. This unit permits an unskilled operator to trace over a sketch or blueprint (see fig. 3) and record the x-y coordinate pair of any point onto a magnetic tape whenever a micro switch is activated. The pictorial figure to be copied is placed on an 18 × 40 inch table, and the shape is traced out manually with a free moving metal sighting ring wired to a high frequency source. An automatic servo system beneath the table surface accurately follows the inertia-less ring, and feeds position signals to the magnetic tape drive with a resolution of 0.1 mm. An auxiliary 16 switch keyboard permits digital input to precede each pictorial group and assign it to a particular stack which may be referenced later. A processing program punches cards from the tape in the appropriate format for either HICAMP or HICAMPER, so that the figure can be manipulated under animated control. The former method for the procedure described above was to sketch the figure on cross hatched paper, read off the coordinates visually, and keypunch this data onto cards. The digitizer reduces the time involved in this process by as much as 2 orders of magnitude!
Steroscopic animations can be produced by creating 2 slightly divergent views of a three-dimensional object using HICAMPER. Two viewing points are chosen at approximately the interpupillary distance (about three inches) apart, and perspective views corresponding to both left and right eye images are displayed on the crt screen (see fig. 4). When viewed through an image splitter (the author uses a pair of weak binoculars sighted from the objective lens end), an illusion of three-dimensional sight is perceived. The illusion seems especially real when the object is programmed to move about. This method, of course, can be extended to movies, but the position of the viewer is critical in the stereogram method above, so an anaglyph technique is used. Both left and right component images are super-imposed on the film, but each is exposed through a separate polaroid filter. Each person in the audience wears a pair of corrective polaroid filter glasses to fuse the images together.
Computer animations are relatively cheaper (by a factor of 20) than movies produced in the conventional way, and many subjects are tedious to draw regardless of the budget. Perspective views of an algebraic function in motion are difficult if not impossible to draw accurately in motion; such a subject has been programmed with ease using HICAMPER. The title of this film is Integration Over a Solid of Revolution (see figs. 5 & 6).
Other subjects may involve intricate shapes with linear, but precise motions. These scenes are laborious to redraw from many frames, especially with varying size presentations. A movie entitled The Game of Chess was programmed to illustrate this facility (see fig. 7).
1. Anderson, S.E., "A Graphical Programming Language for Computer Generation of Incremental Plots and Animated Motion Pictures'', Master's Thesis, Syracuse University, 1968.
2. Anderson, S.E., C.A.L.D. and C.A.P.E.R. Instruction Manuals, Tech-Report TR-67-6, Syracuse University Electrical Engineering Dept., Syracuse, New York, 1967.
3. Anderson, S.E., "A List Processing System for Effectively Storing Computer Animated Pictures", UAIDE Proceedings, Oct. 1968, pp. 205-219.
4. Weiner, D.D. and Anderson, S.E., "A Computer Animation Movie Language for Educational Motion Pictures", Proc. of the FJCC, AFIPS, Vol. 33, 1968, pp. 1317-1320.
