megademo: re-use some infrastructure from fireworks demo

megademo/Makefile

@@ -21,7 +21,7 @@ MEGADEMO:	megademo.o
 
 megademo.o:	megademo.s \
 	zp.inc hardware.inc \
-	gr_offsets.s \
+	gr_hline.s gr_offsets.s vapor_lock.s \
 	c64_opener.s c64.img.lz4 \
 	falling_apple.s apple_40_96.inc
 	ca65 -o megademo.o megademo.s -l megademo.lst

megademo/falling_apple.s

@@ -73,62 +73,11 @@ falling_apple:
 	; setup graphics for vapor lock
 	;==============================
 
-	; Clear Page0
-	lda	#$0
-	sta	DRAW_PAGE
-	lda	#$44
-	jsr	clear_gr
-
-	; Make screen half green
-	lda	#$11
-	ldy	#24
-	jsr	clear_page_loop
-
-
-	;=====================================================
-	; attempt vapor lock
-	;  by reading the "floating bus" we can see most recently
-	;  written value of the display
-	; we look for $55 (which is the grey line)
-	;=====================================================
-	; See:
-	;	Have an Apple Split by Bob Bishop
-        ;	Softalk, October 1982
-
-	; Challenges: each scan line scans 40 bytes.
-	; The blanking happens at the *beginning*
-	; So 65 bytes are scanned, starting at adress of the line - 25
-
-	; the scan takes 8 cycles, look for 4 repeats of the value
-	; to avoid false positive found if the horiz blanking is mirroring
-	; the line (max 3 repeats in that case)
-
-vapor_lock_loop:		; first make sure we have all zeroes
-	LDA #$11
-zxloop:
-	LDX #$04
-wiloop:
-	CMP $C051
-	BNE zxloop
-	DEX
-	BNE wiloop
-
-	LDA #$44		; now look for our border color (4 times)
-zloop:
-	LDX #$04
-qloop:
-	CMP $C051
-	BNE zloop
-	DEX
-	BNE qloop
-
-	; found first line of black after green, at up to line 26 on screen
-        ; so we want roughly 22 lines * 4 = 88*65 = 5720 + 4550 = 10270
-	; - 65 (for the scanline we missed) = 10205 - 12 = 10193
+	jsr	vapor_lock			; 6?
 
 	jsr	gr_copy_to_current		; 6+ 9292
-	; 10193 - 9298 = 895
-	; Fudge factor (unknown) -30 = 865
+	; 10193 - 9298 = 889
+	; Fudge factor (unknown) -24 = 865
 
 	; GR part
 	bit	LORES							; 4
@@ -237,43 +186,6 @@ loop2:
 	rts							; 6
 
 
-
-	;==================================
-	; HLINE
-	;==================================
-
-	; Color in A
-	; Y has which line
-hline:
-	pha							; 3
-	ldx	gr_offsets,y					; 4+
-	stx	hline_loop+1					; 4
-	lda	gr_offsets+1,y					; 4+
-	clc							; 2
-	adc	DRAW_PAGE					; 3
-	sta	hline_loop+2					; 4
-	pla							; 4
-	ldx	#39						; 2
-hline_loop:
-	sta	$5d0,X		; 38				; 5
-	dex							; 2
-	bpl	hline_loop					; 2nt/3
-	rts							; 6
-
-	;==========================
-	; Clear gr screen
-	;==========================
-	; Color in A
-clear_gr:
-	ldy	#46
-clear_page_loop:
-	jsr	hline
-	dey
-	dey
-	bpl	clear_page_loop
-	rts
-
-
 .include "../asm_routines/gr_unrle.s"
 .include "gr_copy.s"
 

megademo/gr_copy.s

@@ -4,7 +4,7 @@
 	; copy 0xc00 to DRAW_PAGE
 	;
 	; 45 + 2 + 120*(8*9 + 5) -1 + 6 = 9292
-
+.align	$100
 gr_copy_to_current:
 
 	lda	DRAW_PAGE					; 3

megademo/gr_hline.s

@@ -0,0 +1,34 @@
+	;==================================
+	; HLINE
+	;==================================
+
+	; Color in A
+	; Y has which line
+hline:
+	pha							; 3
+	ldx	gr_offsets,y					; 4+
+	stx	hline_loop+1					; 4
+	lda	gr_offsets+1,y					; 4+
+	clc							; 2
+	adc	DRAW_PAGE					; 3
+	sta	hline_loop+2					; 4
+	pla							; 4
+	ldx	#39						; 2
+hline_loop:
+	sta	$5d0,X		; 38				; 5
+	dex							; 2
+	bpl	hline_loop					; 2nt/3
+	rts							; 6
+
+	;==========================
+	; Clear gr screen
+	;==========================
+	; Color in A
+clear_gr:
+	ldy	#46
+clear_page_loop:
+	jsr	hline
+	dey
+	dey
+	bpl	clear_page_loop
+	rts

megademo/megademo.s

@@ -36,3 +36,6 @@ loop_forever:
 	.include	"c64_opener.s"
 	.include	"falling_apple.s"
 	.include	"gr_offsets.s"
+	.include	"gr_hline.s"
+	.include	"vapor_lock.s"
+

megademo/vapor_lock.s

@@ -0,0 +1,58 @@
+	;==============================
+	; setup graphics for vapor lock
+	;==============================
+vapor_lock:
+
+	; Clear Page0
+	lda	#$0
+	sta	DRAW_PAGE
+	lda	#$44
+	jsr	clear_gr
+
+	; Make screen half green
+	lda	#$11
+	ldy	#24
+	jsr	clear_page_loop
+
+
+	;=====================================================
+	; attempt vapor lock
+	;  by reading the "floating bus" we can see most recently
+	;  written value of the display
+	; we look for $55 (which is the grey line)
+	;=====================================================
+	; See:
+	;	Have an Apple Split by Bob Bishop
+        ;	Softalk, October 1982
+
+	; Challenges: each scan line scans 40 bytes.
+	; The blanking happens at the *beginning*
+	; So 65 bytes are scanned, starting at adress of the line - 25
+
+	; the scan takes 8 cycles, look for 4 repeats of the value
+	; to avoid false positive found if the horiz blanking is mirroring
+	; the line (max 3 repeats in that case)
+
+vapor_lock_loop:		; first make sure we have all zeroes
+	LDA #$11
+zxloop:
+	LDX #$04
+wiloop:
+	CMP $C051
+	BNE zxloop
+	DEX
+	BNE wiloop
+
+	LDA #$44		; now look for our border color (4 times)
+zloop:
+	LDX #$04
+qloop:
+	CMP $C051
+	BNE zloop
+	DEX
+	BNE qloop
+
+	rts
+
+
+