; vi:filetype=z80:
	section code,"c"

	include defs.inc

main:
	call init

	ld hl, FB_ADDR + 25
	call draw_logo
	call drawbg

.mainloop:
	jr .mainloop

init:
	; setup attributes
	ld hl, ATTR_ADDR
	ld a, $47
	ld b, 24
.attry:	ld c, 32
.attrx:	ld (hl), a
	inc hl
	dec c
	jr nz, .attrx
	dec b
	jr nz, .attry

	; clear screen
	ld hl, FB_ADDR
	xor a
	ld b, 192
.clry:	ld c, 32
.clrx:	ld (hl), a
	inc hl
	dec c
	jr nz, .clrx
	dec b
	jr nz, .clry

	; set border
	out (ULA_PORT), a
	
	ret

; expects X -> c, Y -> b, returns in de
calc_cell_addr:
	push af
	sla b
	sla b		; change from blocks to pixels
	sla b
	; construct low address byte -> e
	ld a, b		; start with Y
	sla a
	sla a
	and $e0		; keep top 3 bits
	ld e, a		; move into e
	ld a, c		; a <- X
	and $1f		; keep low 5 bits
	or e		; combine with Y bits
	ld e, a		; move the result back to e
	; construct high address byte -> d
	ld a, b		; start with Y again
	sra a
	sra a
	sra a
	and $18		; keep bits 3 and 4
	ld d, a		; keep it in d
	ld a, b		; grap Y one more time
	and $7		; keep low 3 bits of Y in a
	or d		; combine with Y6-Y7
	ld bc, FB_ADDR
	or b		; combine with high byte of fb address
	ld d, a		; move result back to d
	pop af
	ret

	; hl: dest
draw_logo:
	push hl
	ld de, logo
	ld b, 16
.logoy:	ld c, 7
	push bc
.logox: ld a, (de)
	ld (hl), a
	inc de
	inc l
	dec c
	jr nz, .logox
	ld bc, 7
	sbc hl, bc
	inc h

	ld a, h
	and $e7
	ld h, a 
	and $7
	jr nz, .skipinc
	ld a, l
	add $20
	ld l, a
.skipinc:
	pop bc
	dec b
	jr nz, .logoy
	pop hl

	; attr
	ld a, h
	srl a
	srl a
	srl a
	or $58
	ld h, a
	ld a, $42

	push hl
	pop ix
	ld b, 7
.sattr:	ld (ix), a
	ld (ix + 32), a
	inc ix
	dec b
	jr nz, .sattr
	ret

	; de: dest
	; a: char
putchar:
	; is it a digit?
	sub '0'
	ret c
	cp 11
	jr nc, .notdigit
	push bc
	ld bc, glyph_0
	jr .common
.notdigit:
	; is it A-Z ?
	sub 'A'-'0'
	ret c
	cp 30
	ret nc
	push bc
	ld bc, glyph_a
.common:
	push de
	push hl
	sla a
	sla a
	sla a
	ld h, 0
	ld l, a
	add hl, bc
	ld c, 8
.chartop:
	ld a, (hl)
	ld (de), a
	inc d
	inc hl
	dec c
	jr nz, .chartop
	pop hl
	pop de
	pop bc
	ret

	; de: dest
	; hl: str
putstr:
	push de
	push bc
.loop:	xor a
	ld b, (hl)
	cp b
	jr z, .done
	ld a, b
	call putchar
	inc hl
	inc e
	jr .loop
.done:	pop bc
	pop de
	ret

	; de: dest
	; a: number
putbin8:
	push de
	push bc
	ld b, 8
.loop:	rlca
	push af
	and 1
	add '0'
	call putchar
	pop af
	inc e
	dec b
	jr nz, .loop
	pop bc
	pop de
	ret

putbin5:
	push de
	push bc
	ld b, 5
	rlca
	rlca
	rlca
	jr putbin8.loop

	; hl: string
	; return -> a
strlen:
	push hl
	xor a
	ld b, a
.loop:	cp (hl)
	jr z, .done
	inc hl
	inc b
	jr .loop
.done:	ld a, b
	pop hl
	ret

	include glyphs.inc
	include logo.inc
	include tiles.inc