pt3: visualize: we have fire

pt3_player/Makefile

@@ -44,7 +44,8 @@ PT3_PLAYER:	pt3_player.o
 	ld65 -o PT3_PLAYER pt3_player.o -C ../linker_scripts/apple2_1000.inc
 
 pt3_player.o:	pt3_player.s \
-	gr_fast_clear.s pt3_lib.s interrupt_handler.s fire.s zp.inc
+	gr_fast_clear.s pt3_lib.s interrupt_handler.s random16.s fire.s \
+	zp.inc
 	ca65 -o pt3_player.o pt3_player.s -l pt3_player.lst
 
 #

pt3_player/fire.s

@@ -17,12 +17,11 @@ fire_init:
 clear_fire_loop:
 
 	lda	#0
-	ldy	#40
+	ldy	#39
 clear_fire_line_loop:
-	beq	done_fire_line_loop
 	sta	(FIRE_FB_L),Y
 	dey
-	jmp	clear_fire_line_loop
+	bpl	clear_fire_line_loop
 done_fire_line_loop:
 
 	clc
@@ -96,12 +95,18 @@ fire_fb_update:
 	ldy	#39
 fire_fb_update_loop:
 
+	jsr	random16
+
+	lda	SEEDL
+	and	#$1
+	sta	FIRE_Q
+
 	; get next line color
 	lda	(FIRE_FB2_L),Y
 
 	; adjust it
-	clc
-	adc	#$ff
+	sec
+	sbc	FIRE_Q
 
 	; saturate to 0
 	bpl	fb_positive

pt3_player/pageflip.s

@@ -0,0 +1,24 @@
+	;==========
+	; page_flip
+	;==========
+
+page_flip:
+	lda	DISP_PAGE						; 3
+	beq	page_flip_show_1					; 2nt/3
+page_flip_show_0:
+        bit	PAGE0							; 4
+	lda	#4							; 2
+	sta	DRAW_PAGE	; DRAW_PAGE=1				; 3
+	lda	#0							; 2
+	sta	DISP_PAGE	; DISP_PAGE=0				; 3
+	rts								; 6
+page_flip_show_1:
+	bit	PAGE1							; 4
+	sta	DRAW_PAGE	; DRAW_PAGE=0				; 3
+	lda	#1							; 2
+	sta	DISP_PAGE	; DISP_PAGE=1				; 3
+	rts								; 6
+							;====================
+							; DISP_PAGE=0 	26
+							; DISP_PAGE=1	24
+

pt3_player/pt3_player.s

@@ -588,7 +588,7 @@ song_list:
 .include	"interrupt_handler.s"
 .include	"pt3_lib.s"
 .include	"fire.s"
-
+.include	"random16.s"
 
 ;=========
 ; strings

pt3_player/random16.s

@@ -0,0 +1,60 @@
+; 16-bit 6502 Random Number Generator
+
+; Linear feedback shift register PRNG by White Flame
+; http://codebase64.org/doku.php?id=base:small_fast_16-bit_prng
+
+; The Apple II KEYIN routine increments this field
+; while waiting for keypress
+
+;SEEDL = $4E
+;SEEDH = $4F
+
+XOR_MAGIC = $7657	; "vW"
+
+	;=============================
+	; random16
+	;=============================
+	; takes:
+	;	not 0, cc = 5+  = 27
+	;	not 0, cs = 5+12+19 = 36
+	;	$0000	  = 5+7+19 = 31
+	;	$8000     = 5+6+14 = 25
+	;	$XX00	  = 5+6+7+19 = 37
+random16:
+
+	lda	SEEDL							; 3
+	beq	lowZero		; $0000 and $8000 are special values	; 2
+
+	asl	SEEDL		; Do a normal shift			; 5
+	lda	SEEDH							; 3
+	rol								; 2
+	bcc	noEor							; 2
+
+doEor:
+				; high byte is in A
+
+
+	eor	#>XOR_MAGIC						; 2
+	sta	SEEDH							; 3
+	lda	SEEDL							; 3
+	eor	#<XOR_MAGIC						; 2
+	sta	SEEDL							; 3
+	rts								; 6
+
+lowZero:
+									; 1
+	lda	SEEDH							; 3
+	beq	doEor		; High byte is also zero		; 3
+				; so apply the EOR
+									; -1
+				; wasn't zero, check for $8000
+	asl								; 2
+	beq	noEor		; if $00 is left after the shift	; 2
+				; then it was $80
+	bcs	doEor		; else, do the EOR based on the carry	; 3
+
+noEor:
+									; 1
+	sta	SEEDH							; 3
+
+	rts								; 6

pt3_player/zp.inc

@@ -35,6 +35,9 @@ CSWH	EQU $37
 KSWL	EQU $38		; key in routine
 KSWH	EQU $39
 
+SEEDL	EQU	$4E
+SEEDH	EQU	$4F
+
 
 ; dos33 zero page = 26-2f, 35-38, 3e 3f 40-4d 
 ; overlap applesoft  67-6a,6f,70,af,b0,ca-cd,d8 
@@ -120,6 +123,7 @@ FIRE_FB_H	EQU $A5
 FIRE_FB2_L	EQU $A6
 FIRE_FB2_H	EQU $A7
 FIRE_FB_LINE	EQU $A8
+FIRE_Q		EQU $A9
 
 ; More zero-page addresses
 ; we try not to conflict with anything DOS, MONITOR or BASIC related