10 REM  'CIRCLES'  IN BASIC
20 IFPEEK(49152)<>76THENLOAD"HIRES",8,1
100 :
110 HIRES=12*4096:DRAW=HI+3:PLOT=DR+3
120 MOVE=PL+3:CLSCR=MO+3:DMODE=CL+3
130 SELPC=DM+3:COLOUR=SE+3:BOX=CO+3
140 TEXT=BO+3:PRNT=TE+3:CHSET=PR+3
150 TRAP=CH+3
160 :
170 REM  BASIC CIRCLES - POLYGONS
180 SYS HIRES,0,1,6
190 XC=160:YC=100:XR=99:YR=79
200 SA=0 :EA=360:INC=5
210 Z1=SA*(null)/180:Z2=EA*(null)/180:Z3=INC*(null)/180
220 X=XC+XR*COS(Z1):Y=YC+YR*SIN(Z1)
230 SYS MOVE,X,Y
240 FOR I=Z1TOZ2 STEPZ3
250   X=XC+XR*COS(I):Y=YC+YR*SIN(I)
260   SYS DRAW,X,Y
270 NEXT
280 SYS PRNT,16,12,"POLYGONS"
290 FOR T=1TO2000:NEXT
300 :
310 REM  BASIC CIRCLES - POTENTIAL
320 SYS HIRES,0,1,6
330 XC=160:YC=100:XR=99:YR=79
340 PHI%=0:YPHI%=0:XYPHI%=0:Y%=0:X%=XR
350 F=0:IF XR<YR THEN F=1
360 IF F=1 THEN X%=YR:TM=XR:XR=YR:YR=TM
370 REM  START LOOP
380   YPHI%=PHI%+Y%+Y%+1
390   XYPHI%=YPHI%-X%-X%+1
400   IF F=0 THEN X2=X%:X3=Y%
410   IF F=1 THEN Y3=X%:Y2=Y%
420   T2%=X%:T1%=T2%*YR/XR
430   IF F=0 THEN Y3=T1%
440   IF F=1 THEN X2=T1%
450   T2%=Y%:T1%=T2%*YR/XR
460   IF F=0 THEN Y2=T1%
470   IF F=1 THEN X3=T1%
480   :
490   SYS PLOT,XC+X2,YC+Y2
500   SYS PLOT,XC-X2,YC+Y2
510   SYS PLOT,XC-X2,YC-Y2
520   SYS PLOT,XC+X2,YC-Y2
530   :
540   SYS PLOT,XC+X3,YC+Y3
550   SYS PLOT,XC-X3,YC+Y3
560   SYS PLOT,XC-X3,YC-Y3
570   SYS PLOT,XC+X3,YC-Y3
580 :
590   PHI%=YPHI%:Y%=Y%+1
600   IF ABS(XYPHI%)<ABS(YPHI%) THEN PHI%=XYPHI%:X%=X%-1
610   IF X%>Y% GOTO 380 'LOOP FOR MORE
620 :
630 SYS PRNT,16,12,"POTENTIAL"
640 FOR T=1TO2000:NEXT
650 END