100 REM  'HIRES'  CIRCLE - POTENTIAL
110 REM  SOURCE FILE BY ANTHONY BRYANT
120 SYS 700
130 .OPT N
140 ;
150 ;
160 ;"HIRES" VARIABLES BY G.KIZIAK
170 X1   = $C027 ;CURRENT POSITION
180 Y1   = $C029
190 X2   = $C02B ;NEW POSITION
200 Y2   = $C02D
210 XC   = $C02F ;CIRC CENTRE (ALSO BOX)
220 YC   = $C031
230 HM   = $C035 ;HIRES/MULTI FLAG
240 ;
250 ;
260 ;"HIRES" INTERNAL SUBROUTINES
270 IGETI =$C17C ;INTERNAL GET INTEGER
280 IEGET =$C187 ;INTERNAL EAT & GET X,Y
290 MOVE  =$C26E ;'MOVE' RTN
300 IMOV  =$C271 ;INTERNAL MOVETO X1,Y1
310 IPLT  =$C375 ;INTERNAL PLOT
320 IDRW  =$C42B ;INTERNAL DRAWTO
330 ;
340 ;ZERO PAGE LABELS
350 T1 = $22
360 T2 = $24
370 FLAG = $26
380 X  = $27
390 Y  = $29
400 PHI = $57
410 PHIY = $59
420 PHIXY = $5B
430 ;
440 *=$8000    ;545 BYTES
450 ;
460 XR  .WOR 0  ;X RADIUS
470 YR  .WOR 0  ;Y RADIUS
480 X3  .WOR 0  ;POTENTIAL Y
490 Y3  .WOR 0  ;POTENTIAL X
500 ;
510 ;SUBROUTINE MOVETO XC,YC
520 MOVC LDX #3
530 LDA X2,X
540 STA XC,X
550 DEX
560 BPL MOVC+2
570 RTS
580 ;
590 ;SUBROUTINE MOVETO XR,YR
600 MOVR LDX #3
610 LDA X2,X
620 STA XR,X
630 DEX
640 BPL MOVR+2
650 RTS
660 ;
670 ;SYS CIRCLE,XC,YC,XR,YR
680 CIRCLE = *
690 JSR IEGET
700 JSR MOVC ;MOVETO XC,YC
710 JSR IEGET
720 JSR MOVR ;MOVETO XR,YR
730 LDA #0
740 STA FLAG
750 STA PHI
760 STA PHI+1
770 STA Y
780 STA Y+1
790 ;
800 CASES LDA XR
810 STA X    ;X=XR
820 CMP YR
830 LDA XR+1
840 STA X+1
850 SBC YR+1
860 BCS LOOP  ;BRANCH IF XR >= YR
870 SWAP  LDA #$FF
880 STA FLAG
890 LDA YR
900 STA X
910 TAX      ;X=YR
920 LDA YR+1
930 STA X+1
940 TAY      ;AND SWAP
950 LDA XR
960 STA YR
970 STX XR   ; XR WITH YR
980 LDA XR+1
990 STA YR+1
1000 STY XR+1
1010 ;
1020 LOOP = * ;MAIN LOOP START
1030 LDX Y+1
1040 STX PHIY+1
1050 LDA Y
1060 ASL      ;PHIY=PHI+Y+Y+1
1070 ROL PHIY+1
1080 SEC
1090 ADC PHI
1100 STA PHIY
1110 LDA PHIY+1
1120 ADC PHI+1
1130 STA PHIY+1
1140 LDX X+1
1150 STX PHIXY+1
1160 LDA X
1170 ASL      ;PHIXY=PHIY-X-X+1
1180 ROL PHIXY+1
1190 STA PHIXY
1200 CLC
1210 LDA PHIY
1220 SBC PHIXY
1230 STA PHIXY
1240 LDA PHIY+1
1250 SBC PHIXY+1
1260 STA PHIXY+1
1270 ;
1280 LDA X
1290 LDX X+1
1300 LDY FLAG
1310 BMI ALTN
1320 STA X2
1330 STX X2+1
1340 JSR SCALE
1350 STA Y3
1360 STX Y3+1
1370 LDA Y
1380 LDX Y+1
1390 STA X3
1400 STX X3+1
1410 JSR SCALE
1420 STA Y2
1430 STX Y2+1
1440 JMP DOPLT
1450 ALTN STA Y3
1460 STX Y3+1
1470 JSR SCALE
1480 STA X2
1490 STX X2+1
1500 LDA Y
1510 LDX Y+1
1520 STA Y2
1530 STX Y2+1
1540 JSR SCALE
1550 STA X3
1560 STX X3+1
1570 ;
1580 DOPLT JSR PLOT4
1590 LDA X3
1600 LDX X3+1
1610 STA X2
1620 STX X2+1
1630 LDA Y3
1640 LDX Y3+1
1650 STA Y2
1660 STX Y2+1
1670 JSR PLOT4
1680 ;
1690 INC Y
1700 BNE J1
1710 INC Y+1  ;Y=Y+1
1720 J1 LDA PHIY
1730 LDX PHIY+1 ;PHI=PHIY
1740 STA PHI
1750 STX PHI+1
1760 ABS1 JSR ABSV   ;TAKE ABS(PHIY)
1770 STA T2
1780 STX T2+1
1790 LDA PHIXY
1800 LDX PHIXY+1
1810 ABS2 JSR ABSV   ;TAKE ABS(PHIXY)
1820 STA T1
1830 STX T1+1
1840 ;
1850 DOIF LDA T1    ;IF ABS(PHIXY)
1860 CMP T2    ; < ABS(PHIY)
1870 LDA T1+1
1880 SBC T2+1  ;THEN ...
1890 BCS ELSE  ;ELSE ...
1900 THEN LDA PHIXY
1910 LDX PHIXY+1
1920 STA PHI
1930 STX PHI+1 ;PHI=PHIXY
1940 LDA X
1950 BNE J2
1960 DEC X+1
1970 J2 DEC X  ;X=X-1
1980 ELSE LDA X    ;IF X >= Y
1990 CMP Y    ;THEN LOOP
2000 LDA X+1
2010 SBC Y+1
2020 BCC STOP ;ELSE STOP
2030 JMP LOOP
2040 STOP RTS
2050 ;
2060 ;SUBROUTINE  REFLECT POINTS & PLOT
2070 PLOT4 = *
2080 LDA XC
2090 CLC
2100 ADC X2
2110 STA X1
2120 PHA
2130 LDA XC+1
2140 ADC X2+1
2150 STA X1+1
2160 PHA
2170 LDA YC
2180 CLC
2190 ADC Y2
2200 STA Y1
2210 LDA YC+1
2220 ADC Y2+1
2230 STA Y1+1
2240 JSR IPLT
2250 LDA XC
2260 SEC
2270 SBC X2
2280 STA X1
2290 LDA XC+1
2300 SBC X2+1
2310 STA X1+1
2320 JSR IPLT
2330 LDA YC
2340 SEC
2350 SBC Y2
2360 STA Y1
2370 LDA YC+1
2380 SBC Y2+1
2390 STA Y1+1
2400 JSR IPLT
2410 PLA
2420 STA X1+1
2430 PLA
2440 STA X1
2450 JMP IPLT
2460 ;
2470 ;SUBROUTINE ABSOLUTE VALUE
2480 ABSV BPL ABOK
2490 CLC
2500 EOR #$FF
2510 ADC #1
2520 PHA
2530 TXA
2540 EOR #$FF
2550 ADC #0
2560 TAX
2570 PLA
2580 ABOK RTS
2590 ;
2600 ;SUBROUTINE TO SCALE OFFSET
2610 SCALE = *     ;T1=T2*YR/XR
2620 STA T2
2630 STX T2+1
2640 LDA #0
2650 STA T1
2660 STA T1+1
2670 LDX #17
2680 CLC  ;16 BIT INTEGER MATH
2690 MULLP ROR T1+1
2700 ROR T1
2710 ROR T2+1
2720 ROR T2
2730 BCC DECN1
2740 CLC
2750 LDA YR
2760 ADC T1
2770 STA T1
2780 LDA YR+1
2790 ADC T1+1
2800 STA T1+1
2810 DECN1  DEX
2820 BNE MULLP
2830 LDA XR
2840 ORA XR+1
2850 BEQ ERROR
2860 LDA #0
2870 STA T1
2880 STA T1+1
2890 LDX #16      ;16 BIT INTEGER MATH
2900 DIVLP ROL T2
2910 ROL T2+1
2920 ROL T1
2930 ROL T1+1
2940 SEC
2950 LDA T1
2960 SBC XR
2970 TAY
2980 LDA T1+1
2990 SBC XR+1
3000 BCC DECN2
3010 STY T1
3020 STA T1+1
3030 DECN2  DEX
3040 BNE DIVLP
3050 ROL T2
3060 ROL T2+1
3070 LDA T2
3080 LDX T2+1
3090 RTS
3100 ERROR JMP $BB8A ;"DIVISION BY ZERO"
3110 ;
3120 .END