oam_meta_spr_pal.s

.importzp TEMP, _oam_off, sp
.import popa, popax
.include "nes.inc"
.include "zpvars.inc"

;void __fastcall__ oam_meta_spr_pal(unsigned char x,unsigned char y,unsigned char pal,const unsigned char *metasprite);

.export _oam_meta_spr_pal

_oam_meta_spr_pal:

	sta <PTR
	stx <PTR+1

	ldy #2				;three popa calls replacement, performed in reversed order
	lda (sp),y
	dey
	sta <SCRX
	lda (sp),y
	dey
	sta <SCRY
	lda (sp),y
	sta <DST			;this is palette, just repurposing RAM variable name

	ldx _oam_off

@1:

	lda (PTR),y			;x offset
	cmp #$80
	beq @2
	iny
	clc
	adc <SCRX
	sta OAM_BUF+3,x
	lda (PTR),y			;y offset
	iny
	clc
	adc <SCRY
	sta OAM_BUF+0,x
	lda (PTR),y			;tile
	iny
	sta OAM_BUF+1,x
	lda (PTR),y			;attribute
	iny
	and #$fc			;remove palette bits
	ora <DST			;add new palette bits
	sta OAM_BUF+2,x
	inx
	inx
	inx
	inx
	jmp @1

@2:

	stx _oam_off
	
	lda <sp
	adc #2				;carry is always set here, so it adds 3
	sta <sp
	bcc @3
	inc <sp+1

@3:

	rts