4
Pattern Maker
There is not a lot that one can say about this program. There are many similar pattern-drawing programs published and available, but just when one thinks one has got this one sorted out and can predict more or less what it is going to do next, it goes and does something different. Part of the interest is that, like the previous program, much play is made of switching colours. As a consequence, the program may redraw the entire display in black (invisibly) before abruptly revealing it. Occasionally at the beginning it may switch itself to black for some time, so don't be afraid of pressing the ESCAPE key and then restarting it. Another point is that the program needs to run for at least ten minutes, especially in order to allow background colours to develop, when of course the all-black display is very much a rarity.
If you try changing line 20 to Mode 2, more colours are available on the screen at once, but the definition is chunkier. In addition, some moire patterns are not discernible. Actually, you can play around with quite a few lines, especially 50, 80, 90, 100 and 240, changing the numeric values in these lines. You can also try the effect of removing the duplicated line at 130. Have fun!
10 REM Pattern Maker
20 MODE1
30 VDU29,640;512;
40 REPEAT
50 GCOLRND(5)-1,RND(8)-1
60 X%=510
70 Y%=0
80 I%=RND(30)+4
90 P%=(RND(11)-1)*8+3+RND(4)
100 L%=RND(500)
110 REPEAT
120 MOVE0,0
130 MOVE0,0
140 PLOTP%,X%,Y%
150 MOVE0,0
160 PLOTP%,X%,-Y%
170 MOVE0,0
180 PLOTP%,-X%,-Y%
190 MOVE0,0
200 PLOTP%,-X%,Y%
210 X%=X%-I%
220 Y%=Y%+I%
230 UNTIL X%<L%
240 VDU19,RND(8)-1,RND(8)-1,0,0,0
250 UNTIL0