ORG	$4357
; SYS 17239 or CALL 17239

EMPTY2	=	$00
TREE2	=	$44
FIRE2	=	$99

; common available zero page


GBASL	=	$26
GBASH	=	$27

SEED2	=	$28
SEED0	=	$29
SEED1	=	$2A

H2	=	$2B
V2	=	$2C
PLOTC	=	$2D
COLOR	=	$2E
PAGE	=	$2F
TOPL	=	$30
TOPH	=	$31
MIDL	=	$32
MIDH	=	$33
BTML	=	$34
BTMH	=	$35
PLOTL	=	$36
PLOTH	=	$37
lastzp	=	$38

tablelo	=	$5000
tablehi = tablelo+25

	JSR START
	STA V2
	LDA #$4C ; JMP instruction
	STA SEED2 ; temporary JMP
	LDX #$00 ; y coord
table:
	TXA
	JSR SEED2 ; temporary JMP GBASCALC
	LDA GBASL
	STA tablelo,X
	LDA GBASH
	STA tablehi,X
	LDY #$00
	TYA
clrline:
	STA (GBASL),Y
	INY
	CPY #40
	BNE clrline

	INX
	CPX V2
	BNE table

	JSR sseed0
	JSR sseed2

	LDX #$60
	STX PAGE
	STX TOPH
	LDY #$00
	STY TOPL
	TYA
zero:	STA (TOPL),Y
	INY
	BNE zero
	INX
	STX TOPH
	CPX #$80
	BNE zero

loop3:
	LDX #0
	STX TOPL
	LDA #41
	STA MIDL
	STA PLOTL
	LDA #83
	STA BTML
	LDA PAGE
	STA TOPH
	STA MIDH
	STA BTMH
	EOR #$10
	STA PLOTH
	STA PAGE
loop2:
	TXA
	STX V2
	LSR       ; F800 PLOT-like...
	; PHP       ; F801
	TAY	 ; save A in Y without touching C
	LDA #$0F
	BCC over2
	ADC #$E0
over2:	STA PLOTC   ; PLOT...
	LDA tablelo,Y ; lookup instead of GBASCALC
	STA GBASL
	LDA tablehi,Y
	STA GBASH
	; PLP     ; continue PLOT
	LDY #$01 ; x coord
loop1:
	STY H2
	LDA (MIDL),Y
	STA (PLOTL),Y
	BEQ empty
	BPL tree
	LDA #EMPTY2
doplot:	LDY H2
	STA (PLOTL),Y
	DEY
	EOR (GBASL),Y
	AND PLOTC
	EOR (GBASL),Y
	STA (GBASL),Y
noplot:
	LDY H2
	INY
	CPY #41
	BNE loop1
	LDA MIDL
	STA TOPL
	LDA MIDH
	STA TOPH
	LDA BTML
	STA MIDL
	STA PLOTL
	CLC
	ADC #42
	STA BTML
	LDA BTMH
	EOR #$10
	STA PLOTH
	EOR #$10		
	STA MIDH
	ADC #$00
	STA BTMH
	LDX V2
	INX
	CPX #48
	BNE loop2
	JSR QUIT
	JMP loop3
empty:
	DEC SEED2
	BNE noplot
	JSR sseed2 ; probability f
	LDA #TREE2
	BNE doplot
ignite:
	LDA #FIRE2
	BNE doplot
tree:
	DEC SEED0
	BNE check
	DEC SEED1
	BNE check
	JSR sseed0 ; probability p
	BNE ignite
check:
	LDA (TOPL),Y ; n
	ORA (BTML),Y ; s
	DEY
	ORA (TOPL),Y ; nw
	ORA (MIDL),Y ; w
	ORA (BTML),Y ; sw
	INY
	INY
	ORA (TOPL),Y ; ne
	ORA (MIDL),Y ; e
	ORA (BTML),Y ; se
	BMI ignite
	BPL noplot

sseed0:
	LDA #$17 ; 1 in 10007 (prime)
	STA SEED0
	LDA #$27
	STA SEED1
	RTS
sseed2:
	LDA #$65  ; 1 in 101 (prime)
	STA SEED2
	RTS

default:
	LDA #<GBASCALC ; setup GBASCALC
	STA SEED0
	LDA #>GBASCALC
	STA SEED1
	LDA #25 ; screen rows
	RTS
GBASCALC:
	LDY #$00
	STY GBASH		
	ASL
	ASL
	ASL
	STA GBASL
	ASL
	ROL GBASH
	ASL
	ROL GBASH
	ADC GBASL
	STA GBASL
	LDA GBASH
	ADC #$04
	STA GBASH
	RTS

QUIT:
	LDA $E000

; APPLE II

	CMP #$4C
	BNE c64quit

	BIT $C000 ; apple ii keypress?
	BPL CONTINUE ; no keypressed then continue
	BIT $C010 ; clear keyboard strobe
	BIT $C051 ; text mode

; end APPLE II specific

ABORT:
	PLA
	PLA

	LDX #GBASL
restorzp:
	LDA $5100,X
	STA $00,X
	INX
	CPX #lastzp
	BNE restorzp

CONTINUE:
	RTS

START:
	LDX #GBASL
savezp:
	LDA $00,X
	STA $5100,X
	INX
	CPX #lastzp
	BNE savezp

; machine ???

	LDA $E000 ; terribly unreliable, oh well

; APPLE II

	CMP #$4C ; apple ii?
	BNE c64start ; nope, try another

	BIT $C056 ; low resolution
	BIT $C052 ; full screen
	BIT $C054 ; page one
	BIT $C050 ; graphics
; GBASCALC = $F847
	LDA #$47
	STA SEED0
	LDA #$F8
	STA SEED1
	LDA #24 ; screen rows
	RTS

; end APPLE II specific

; COMMODORE 64 specific

c64quit:

; COMMODORE 64

	CMP #$85 ; commodore 64?
	BNE CONTINUE ; nope, default to no keypress

	LDA $C6 ; commodore keyboard buffer length
	BEQ CONTINUE ; no keypressed then continue

	LDA #$00
	STA $C6
	LDA $D016 ; Screen control register #2
	AND #$EF  ; Bit #4: 0 = Multicolor mode off.
	STA $D016
	LDA #21 ; default character set
	STA $D018
	BNE ABORT

c64start:

	CMP #$85 ; commodore 64?
	BEQ c64yes ; yes
	JMP default ; no, default to boringness
c64yes:
	LDA #$00  ; black
	STA $D020 ; border
	LDA #$00  ; black
	STA $D021 ; background
	LDA #$05  ; dark green
	STA $D022 ; Extra background color #1
	LDA #$08  ; orange
	STA $D023 ; Extra background color #2
	LDA $D016 ; Screen control register #2
	ORA #$10  ; Bit #4: 1 = Multicolor mode on.
	STA $D016

	LDA #$30  ; 0011 0000 $3000 charset page
	STA PLOTH
	LSR
	LSR
	STA PLOTC ; 0000 1100 #$0C
; 53272 $D018
; POKE 53272,(PEEK(53272)AND240)+12: REM SET CHAR POINTER TO MEM. 12288
;     Bits #1-#3: In text mode, pointer to character memory
;    (bits #11-#13), relative to VIC bank, memory address $DD00
;     %110, 6: $3000-$37FF, 12288-14335.
	LDA $D018
	AND #$F0
	ORA PLOTC
	STA $D018
; setup nine characters

; 00- 00 00
	LDA #$00 ; chr(0) * 8
	STA PLOTL
	; --- LDA #$00 ; already zero
	TAX ; LDX #$00
	JSR charset

; 04- 00 55
	LDA #32 ; chr(4) * 8
	STA PLOTL
	LDA #$55
	; LDX #$00 ; already zero
	JSR charset

; 09- 00 AA
	LDA #72 ; chr(9) * 8
	STA PLOTL
	LDA #$AA
	; LDX #$00 ; already zero
	JSR charset

; 40- 55 00
	LDA PLOTH ; 512 = chr(64) * 8
	CLC
	ADC #$02
	STA PLOTH
	LDX #$00
	STX PLOTL
	LDA #$00
	LDX #$55
	JSR charset

; 44- 55 55
	LDA #32 ; chr(68) * 8
	STA PLOTL
	TXA ; LDA #$55
	; LDX #$55 ; already 55
	JSR charset

; 49- 55 AA
	LDA #72 ; chr(73) * 8
	STA PLOTL
	LDA #$AA
	; LDX #$55 ; already 55
	JSR charset

; 90- AA 00
	LDA PLOTH ; chr(144) * 8
	CLC
	ADC #$02
	STA PLOTH
	LDA #128
	STA PLOTL
	LDA #$00
	LDX #$AA
	JSR charset

; 94- AA 55
	LDA #160 ; chr(148) * 8
	STA PLOTL
	LDA #$55
	; LDX #$AA ; already AA
	JSR charset

; 99- AA AA
	LDA #200 ; chr(153) * 8
	STA PLOTL
	TXA ; LDA #$AA
	; LDX #$AA ; already AA
	JSR charset
	JMP default
charset:
	LDY #$00
chartop:
	STA (PLOTL),Y
	INY
	CPY #$04
	BNE chartop
	TXA
charbtm:
	STA (PLOTL),Y
	INY
	CPY #$08
	BNE charbtm
	RTS

; end COMMODORE 64 specific