` CREATIVE COMPUTING VOL. 9, NO. 3 / MARCH 1983 / PAGE 214`

 Computer art for the Tektronix 4052: part 2. Joe Jacobson. Computer Art For The Tektronix 4052 Thes month I will discuss another polar coordinate program, Sinusoidal Loop Program No. 2. This routine is somewhat similar in structure to Sinusoidal Loop Program No. 1 (Creative Computing, January, 1983) and is used the same way. However, the resulting pictures are quite different. The present program uses three polar coordinate functions that differ from those in the earlier program. Each of these functions is the sum of a constant and a sinusoidal function of the angle. This results in completely new patterns, some of which are visually quite striking. A Basic source listing and some sample output pictures accompany this article. To use this program you will need a Tektronix 4050 series terminal/ computer. However, the algorithm can be adapted for other computer systems if the screen resolution is sufficiently high. Most home computers do not have enough CRT screen resolution; in this case you will need a good mechanical X-Y plotter. Note that the graphics commands (MOVE, DRAW, WINDOW, VIEWPORT) used here are specific to the Tektronix 4050 series computers. The program is easy to use. It prompts the user, asking for values of the input parameters N, L, D, and G. N selects a polar coordinate function. L is an angular frequency coefficient. D is the increment in radius that is added between angular sweeps. G is the increment within an angular sweep. When the program asks for a value of the parameter T1, enter a 1 from the keyboard. The picture will be plotted and a list of input parameter values will be printed at the bottom of the screen for future reference. Then clear the screen and hit RETURN, and the same picture will be plotted again, this time without a parameter list. If you enter a 2 for T1, instead of a 1, you get a "clean' plot (no parameter list) the first time. The program must be run again for each new design you make. Table 1 lists the ranges of input parameters that I have found to give good designs. However, values outside these intervals may also work well. The patterns seem to repeat for L values larger than about 60 (with G=5). Note that L, D, and G can be decimal fractions, such as L = 16.5. This program is one of several I have recently written. The others will appear in future issues. Table: Suggested Parameter Values.