; thick sine

; zero page
GBASL	= $26
GBASH	= $27
YY	= $69
ROW_SUM = $70

HGR_X           = $E0
HGR_XH          = $E1
HGR_Y           = $E2
HGR_COLOR       = $E4
HGR_PAGE        = $E6

FRAME	= $FC
SUM	= $FD
SAVEX	= $FE
SAVEY	= $FF


thick_sine:

	;==================
	; create sinetable

	ldy	#0		; Y is 0
sinetable_loop:
	tya							; 2
	and	#$3f	; wrap sine at 63 entries		; 2

	cmp	#$20
	php		; save pos/negative for later

	and	#$1f

	cmp	#$10
	bcc	sin_left		; blt

sin_right:
	; sec	carry should be set here
	eor	#$FF
	adc	#$20			; 32-X
sin_left:
	tax
	lda	sinetable_base,X				; 4+

	plp
	bcc	sin_done

sin_negate:
	; carry set here
	eor	#$ff
	adc	#0		; FIXME: this makes things off by 1

sin_done:
	sta	sinetable,Y

	iny
	bne	sinetable_loop

	; Y is 0 at this point?

done:
	jmp	done


sinetable_base:
; this is actually (32*sin(x))
.byte $00,$03,$06,$09,$0C,$0F,$11,$14
.byte $16,$18,$1A,$1C,$1D,$1E,$1F,$1F
.byte $20


sinetable=$6000