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Leonardo. Vol. 12, pp. 37-40. Pergamon Press, 1979. Printed in Great Britain. A STUDY IN THE VARIATION OF TYPES OF COMPUTER DRAWINGS OBTAINABLE BY SMALL PROGRAM CHANGES Ana Sacerdote de Guthmann* 1. A digital computer can make a drawing by a point-bypoint procedure. Given the initial location of a series of points describinga basicgeometricalshape orbasic unit,a computer program can direct the computer to develop a drawing from it. This initial point information may be a long list of graphical coordinates of points if the basic shape is complex. However, if the list is very short, describing a simple basic unit, the scope of what can be done using the program is broader and more varied. In my explorations of the potentialities of computer drawing, I employ a very simple basic unit. In my earlier work in the animation of color for cinema film, I followed a similiar principle, employing a basic chromatic unit from which variations were developed [11. Thiswasdone without the aid of a computer, but I believe that the day will come when it will be soaided. My present attention has been to' basic units having simple graphical coordinates. The one I have employed consists of two diagonally opposed right isosceles trianglesjoined at the vertex, a shape that I consider static and insignificant (Fig. 1). I ' ( I I \ I I \ I I I I :-v Fig. 1. The basic unit "Artist, VIDT 2004, Buenos Aires, Argentina. (Received 6 Sept. 1976) I was first interested in obtaining many variations. Of course, the number possible is infinite. I employed the followingtwo ways of varying the basic unit: (1) vary the length of one, two, three or all of its legsand (2)rotateone or both of its axes around point 0. The extent of rotation may be between 0" and 180". Instructions to carry out thesevariations areincorporated in a subroutine, whichis a subprogram that may be called any number of times along with other information by a main program. A number of examplesof variations from the basicunit are shown in Fig. 2. In these examples only changes in length are displayed. Example (e) represents the situation where the two triangles degenerate into a vertical line. Legs DO and OA have decreased to zero length and points A and D have become coincident with point 0.If the change shown by examples(d) and (e) is continued to that shown by example (f), then it is clear that the resulting shape is reversed. Just as the number of possible shapesin the range represented by the extremes(a) and (e) is infinite, so is the number in the range given by the extremes (e) and (i). A seriesof shapes, typefiedby the examplesshown in Fig. 2, may be considered analogous to the drawings comprising a storyboard that indicate importantchanges to be expectedin a planned film or.television production. One shape may be linked to another by a number of transitional shapes to produce a complex computer drawing or an animated film. Also, each shape may be considered as a basic unit (a basic unit of second order) for the generation of computer drawings. For instance, I employed example (8) of Fig. 2 as a basic unit; from it a number of variations were produced that comprise a sequence of drawings related to one another by the computer program. 2. I have found that a change of relativelyfew commands in the program results in strikingly different computer drawings, some of which hardly appear to be related although they are in the same program family. I present here several examples. n b c d e f q h j Fig. 2. Examples of variations o f the basic unit 37 38 Ana Sacerdote de Guthmann Fig. 3. Graphic unit of second order (example g in Fig. 2) submitted to variation, rotation and displacenient along a circular path. The drawing in Fig. 3 shows a spiraleffect. To generate it, points A, B, C and D (Fig. l), denoting the corners of the basic unit taken to be example(8)of Fig. 2, were made to rotate in 8" angular increments about point 0 and points B, C and D were made to vary in...

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