This was a chunk of Applesoft Basic and a chunk of Assembly Language that worked in tandem to put the Apple IIgs in graphics display mode and then transport chunks of memory onto the screen. Its main purpose is to sneak around in memory after rebooting the machine, to examine how the program that was previously running moments earlier was storing its graphics.
Among other controls, it had a "wrapping interval", so you could move chunks of memory onto the display in intervals that matched the width of whatever graphics you were trying to examine. For example, if you were looking at a piece of art that was 80 pixels (40 bytes) wide, you could dial the interval down to 40 and the art would unscramble itself and appear on the screen as the artist intended.
3 S = 8263 4 G = 49193 5 L = 8216 6 POKE G,193 10 D$ = CHR$ (4) 20 PRINT : PRINT D$;"bload ga,a$2000" 30 B = 7:X = 12:P = 9:Y = 246 40 W = 16 50 POKE 0,W: POKE 1,0 60 POKE L,Y: POKE L + 1,X + (P * 16): POKE L + 2,B 70 CALL 8192 75 GET A$ 76 IF A$ = "0" THEN POKE G,65: GOTO 120 80 IF A$ = "4" AND W > 4 THEN W = W - 2 85 IF A$ = "6" AND W < 256 THEN W = W + 2 90 IF A$ = "1" THEN Y = Y - 1: IF Y = - 1 THEN Y = 255:A$ = "8" 92 IF A$ = "3" THEN Y = Y + 1: IF Y = 256 THEN Y = 0:A$ = "2" 94 IF A$ = "8" THEN X = X - 1: IF X = - 1 THEN X = 15:A$ = "7" 96 IF A$ = "2" THEN X = X + 1: IF X = 16 THEN X = 0:A$ = "9" 98 IF A$ = "7" THEN P = P - 1: IF P = - 1 THEN P = 15:A$ = "=" 99 IF A$ = "9" THEN P = P + 1: IF P = 16 THEN P = 0:A$ = "/" 100 IF A$ = "=" AND B > 2 THEN B = B - 1 101 IF A$ = "/" AND B < 34 THEN B = B + 1 102 IF A$ = "+" AND M > 0 THEN M = M - 1: POKE 2,M: CALL S 103 IF A$ = "-" AND M < 190 THEN M = M + 1: POKE 2,M: CALL S 110 GOTO 50 120 PRINT : PRINT "Stopped at:" 121 A = (P * 4096) + (X * 256) + Y 122 C = (M + 1) * W 123 PRINT "Bank:";B: PRINT "Data Width:";W: PRINT "Address:";A 124 PRINT "(Page:";P;")(Line:";X;")(Byte:";Y;")" 125 PRINT "Length marker at:";M 126 PRINT "Lenth x Width = ";C 130 PRINT : PRINT "To capture screen:" 140 PRINT "]mtr" 150 PRINT "*00/100065535 THEN D = D - 65535 186 PRINT MID$ (Q$, INT (A / 4096) + 1,1);:A = A - INT (A / 4096) * 4096 187 PRINT MID$ (Q$, INT (A / 256) + 1,1);:A = A - INT (A / 256) * 256 188 PRINT MID$ (Q$, INT (A / 16) + 1,1);:A = A - INT (A / 16) * 16 189 PRINT MID$ (Q$,A + 1,1);"."; 190 PRINT MID$ (Q$, INT (D / 4096) + 1,1);:D = D - INT (D / 4096) * 4096 191 PRINT MID$ (Q$, INT (D / 256) + 1,1);:D = D - INT (D / 256) * 256 192 PRINT MID$ (Q$, INT (D / 16) + 1,1);:D = D - INT (D / 16) * 16 193 PRINT MID$ (Q$,D + 1,1);"m" 194 PRINT "*bsave funky";W;"w,a$1000,l";C
Here's the Assembly Language portion, which was loaded into memory address $2000.
CLC
XCE
SEP #30 (shortm shortx)
LDA #E1
PHA
PLB
REP #30 (longm longx)
LDA #0000
STA 02
STA 04
STZ 06
LDX 02
LDY 04
LDA 079CF6,X
STA 2000,Y
INX
INX
INY
INY
INC 06
INC 06
LDA 06
CMP 00
BNE 2017 {-15}
LDA 02
CLC
ADC 00
STA 02
LDA 04
CLC
ADC #00A0
CMP #7900
BCC 200F {-2F}
SEP #30 (shortm shortx)
LDA #00
PHA
PLB
SEC
XCE
RTS
CLC
XCE
REP #30 (longm longx)
LDA 02
AND #00FF
STA 02
ASL
ASL
ADC 02
ASL
ASL
ASL
ASL
ASL
ADC 00
TAX
LDA #FEEF
STA E12000,X
SEP #30 (shortm shortx)
SEC
XCE
RTS