ootw: forgot a file

ootw/gr_overlay.s

@@ -0,0 +1,103 @@
+	;=========================================================
+	; gr_overlay, 40x48 version
+	;=========================================================
+	; copy 0xc00 to DRAW_PAGE
+	; then overlay with 0x1000, treating 0xa as transparent
+
+gr_overlay:
+	jsr	gr_copy_to_current
+
+	ldy	#0
+	lda	#40
+	sta	CH		; xsize is in CH			; 3
+	lda	#46
+	sta	CV		; ysize is in CV			; 3
+
+gr_overlay_loop:
+
+	ldy	CV							; 3
+	lda	gr_offsets,Y	; lookup low-res memory address		; 4
+	sta	OUTL		; store out low byte of addy		; 3
+	sta	INL
+	lda	gr_offsets+1,Y	; look up high byte			; 4
+	clc
+	adc	DRAW_PAGE	;					; 3
+	sta	OUTH		; and store it out			; 3
+
+	lda	gr_offsets+1,Y	; look up high byte			; 4
+	clc
+	adc	#$c		; force to start at $1000
+	sta	INH
+
+				; OUTH:OUTL now points at right place
+
+	ldx	CH		; load xsize into x			; 3
+	ldy	#0
+gr_overlay_put_pixel:
+	lda	(INL),Y			; get sprite colors		; 5
+
+	; check if completely transparent
+	; if so, skip
+
+	cmp	#$aa			; if all zero, transparent	; 2
+	beq	gr_overlay_done_draw	; don't draw it			; 2nt/3
+
+	sta	COLOR			; save color for later		; 3
+
+	; check if top pixel transparent
+
+	and	#$f0			; check if top nibble zero	; 2
+	cmp	#$a0
+	bne	gr_overlay_bottom	; if not skip ahead		; 2nt/3
+
+	lda	COLOR
+	and	#$0f
+	sta	COLOR
+
+	lda	#$f0			; setup mask			; 2
+	sta	MASK							; 3
+	bmi	gr_overlay_mask		; always?			; 3
+
+
+gr_overlay_bottom:
+	lda	COLOR			; re-load color			; 3
+	and	#$0f			; check if bottom nibble zero	; 2
+	cmp	#$0a
+	bne	put_sprite_all		; if not, skip ahead		; 2nt/3
+								;=============
+								;	7/8
+
+	lda	COLOR
+	and	#$f0
+	sta	COLOR
+	lda	#$0f							; 2
+	sta	MASK			; setup mask			; 3
+								;===========
+								;         5
+
+gr_overlay_mask:
+	lda	(OUTL),Y		; get color at output		; 5
+	and	MASK			; mask off unneeded part	; 3
+	ora	COLOR			; or the color in		; 3
+	sta	(OUTL),Y		; store it back			; 6
+
+	jmp	gr_overlay_done_draw	; we are done			; 3
+
+put_sprite_all:
+	lda	COLOR			; load color			; 3
+	sta	(OUTL),Y		; and write it out		; 6
+
+
+gr_overlay_done_draw:
+	iny
+	dex				; decrement x counter		; 2
+	bne	gr_overlay_put_pixel	; if not done, keep looping	; 2nt/3
+
+	dec	CV			; decemenet total y count	; 5
+	dec	CV
+	bpl	gr_overlay_loop		; loop if not done		; 2nt/3
+
+
+	rts				; return			; 6
+
+