dos33fsprogs/fancy_lores/disp4048d.s

; Display a 40x48d lo-res image

; Uses the 40x48d page1/page2 every-1-scanline pageflip mode

; by deater (Vince Weaver) <vince@deater.net>

; Zero Page
FRAMEBUFFER	= $00	; $00 - $0F
YPOS		= $10
YPOS_SIN	= $11
CH		= $24
CV		= $25
GBASL		= $26
GBASH		= $27
BASL		= $28
BASH		= $29
FRAME		= $60
BLARGH		= $69
DRAW_PAGE	= $EE
LASTKEY		= $F1
PADDLE_STATUS	= $F2
TEMP		= $FA
WHICH		= $FB

; Soft Switches
KEYPRESS= $C000
KEYRESET= $C010
SET_GR	= $C050 ; Enable graphics
FULLGR	= $C052	; Full screen, no text
PAGE0	= $C054 ; Page0
PAGE1	= $C055 ; Page1
LORES	= $C056	; Enable LORES graphics
PADDLE_BUTTON0 = $C061
PADDL0	= $C064
PTRIG	= $C070

; ROM routines

TEXT	= $FB36				;; Set text mode
HOME	= $FC58				;; Clear the text screen
WAIT	= $FCA8				;; delay 1/2(26+27A+5A^2) us

MAX	= 3

	lda	#$ff
	sta	WHICH

start_over:
	inc	WHICH
	lda	WHICH
	cmp	#MAX
	bne	in_range
	lda	#0
	sta	WHICH

in_range:

	;===================
	; init screen
	jsr	TEXT
	jsr	HOME
	bit	KEYRESET

	;===================
	; init vars

	lda	#0
	sta	DRAW_PAGE

	;=============================
	; Load graphic page0

	lda	#$0c
	sta	BASH
	lda	#$00
	sta	BASL                    ; load image to $c00

	lda	WHICH
	asl
	asl				; which*4
	tay

	lda	pictures,Y
	sta	GBASL
	lda	pictures+1,Y
	sta	GBASH
	jsr	load_rle_gr

	lda	#4
	sta	DRAW_PAGE

	jsr	gr_copy_to_current	; copy to page1

	; GR part
	bit	PAGE1
	bit	LORES							; 4
	bit	SET_GR							; 4
	bit	FULLGR							; 4

	jsr	wait_until_keypressed


	;=============================
	; Load graphic page1

	lda	#$0c
	sta	BASH
	lda	#$00
	sta	BASL                    ; load image to $c00

	lda	WHICH
	asl
	asl				; which*4
	tay

	lda	pictures+2,Y
	sta	GBASL
	lda	pictures+3,Y
	sta	GBASH
	jsr	load_rle_gr

	lda	#0
	sta	DRAW_PAGE

	jsr	gr_copy_to_current

	; GR part
	bit	PAGE0

	jsr	wait_until_keypressed


	;==============================
	; 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	gr_copy_to_current		; 6+ 9292
	; 10193 - 9298 = 895
	; Fudge factor (unknown) -30 = 865

	; GR part
	bit	LORES							; 4
	bit	SET_GR							; 4
	bit	FULLGR							; 4

	; Try X=88 Y=2 cycles=893 R2

	nop
        ldy     #2							; 2
loopA:
        ldx	#88							; 2
loopB:
        dex                                                             ; 2
        bne     loopB                                                   ; 2nt/3

        dey                                                             ; 2
        bne     loopA                                                   ; 2nt/3

        jmp     display_loop
.align  $100


	;================================================
	; Display Loop
	;================================================
	; each scan line 65 cycles
	;       1 cycle each byte (40cycles) + 25 for horizontal
	;       Total of 12480 cycles to draw screen
	; Vertical blank = 4550 cycles (70 scan lines)
	; Total of 17030 cycles to get back to where was

	; We want to alternate between page1 and page2 every 65 cycles
        ;       vblank = 4550 cycles to do scrolling


	; 2 + 48*(  (4+2+25*(2+3)) + (4+2+23*(2+3)+4+5)) + 9)
	;     48*[(6+125)-1] + [(6+115+10)-1]

display_loop:

	ldy	#96						; 2

outer_loop:

	bit	PAGE0						; 4
	ldx	#12		; 65 cycles with PAGE0		; 2
page0_loop:			; delay 61+bit
	dex							; 2
	bne	page0_loop					; 2/3


	; bit(4) -1(fallthrough) + loop*5 -1(fallthrouh)+4 extra = 61
	; 5L = 55

	bit	PAGE1						; 4
	ldx	#11		; 65 cycles with PAGE1		; 2
				;
page1_loop:			; delay 115+(7 loop)+4 (bit)+4(extra)
	dex							; 2
	bne	page1_loop					; 2/3

	dey							; 2
	bne	outer_loop					; 2/3



	;======================================================
	; We have 4550 cycles in the vblank, use them wisely
	;======================================================
	; do_nothing should be      4550+1 -2-9 -7= 4533

	jsr	do_nothing				; 6

	lda	KEYPRESS				; 4
	bpl	no_keypress				; 3
	jmp	start_over
no_keypress:

	jmp	display_loop				; 3



	;=================================
	; do nothing
	;=================================
	; and take 4533-6 = 4527 cycles to do it
do_nothing:

	; Try X=4 Y=174 cycles=4525 R2

	nop	; 2

	ldy	#174							; 2
loop1:
	ldx	#4							; 2
loop2:
	dex								; 2
	bne	loop2							; 2nt/3

	dey								; 2
	bne	loop1							; 2nt/3


	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

gr_offsets:
	.word	$400,$480,$500,$580,$600,$680,$700,$780
	.word	$428,$4a8,$528,$5a8,$628,$6a8,$728,$7a8
	.word	$450,$4d0,$550,$5d0,$650,$6d0,$750,$7d0


.include "../asm_routines/gr_unrle.s"
.include "../asm_routines/keypress.s"
.include "gr_copy.s"

pictures:
	.word apple_low,apple_high
	.word katahdin_low,katahdin_high
	.word spacebars_low,spacebars_high

.include "apple_40_48d.inc"
.include "katahdin_40_48d.inc"
.include "spacebars_40_48d.inc"