1 files changed, 117 insertions, 0 deletions
diff --git a/src/home/bg_map.asm b/src/home/bg_map.asm
new file mode 100644
index 0000000..43dfe7b
--- /dev/null
+++ b/src/home/bg_map.asm
@@ -0,0 +1,117 @@
+; reads structs:
+;   x (1 byte), y (1 byte), data (n bytes), $00
+;   x (1 byte), y (1 byte), data (n bytes), $00
+;   ...
+;   $ff
+; for each struct, writes data to BGMap0-translated x,y
+WriteDataBlocksToBGMap0:
+	call WriteDataBlockToBGMap0
+	bit 7, [hl] ; check for $ff
+	jr z, WriteDataBlocksToBGMap0
+	ret
+
+; reads struct:
+;   x (1 byte), y (1 byte), data (n bytes), $00
+; writes data to BGMap0-translated x,y
+WriteDataBlockToBGMap0:
+	ld b, [hl]
+	inc hl
+	ld c, [hl]
+	inc hl
+	push hl ; hl = addr of data
+	push bc ; b,c = x,y
+	ld b, -1
+.find_zero_loop
+	inc b
+	ld a, [hli]
+	or a
+	jr nz, .find_zero_loop
+	ld a, b ; length of data
+	pop bc ; x,y
+	push af
+	call BCCoordToBGMap0Address
+	pop af
+	ld b, a ; length of data
+	pop hl ; addr of data
+	or a
+	jr z, .move_to_next
+	push bc
+	push hl
+	call SafeCopyDataHLtoDE ; copy data to de (BGMap0 translated x,y)
+	pop hl
+	pop bc
+
+.move_to_next
+	inc b ; length of data += 1 (to account for the last $0)
+	ld c, b
+	ld b, 0
+	add hl, bc ; point to next structure
+	ret
+
+; writes a to [v*BGMap0 + BG_MAP_WIDTH * c + b]
+WriteByteToBGMap0:
+	push af
+	ld a, [wLCDC]
+	rla
+	jr c, .lcd_on
+	pop af
+	push hl
+	push de
+	push bc
+	push af
+	call BCCoordToBGMap0Address
+	pop af
+	ld [de], a
+	pop bc
+	pop de
+	pop hl
+	ret
+.lcd_on
+	pop af
+;	fallthrough
+
+; writes a to [v*BGMap0 + BG_MAP_WIDTH * c + b] during hblank
+HblankWriteByteToBGMap0: ; 06d9
+	push hl
+	push de
+	push bc
+	ld hl, wTempByte
+	push hl
+	ld [hl], a
+	call BCCoordToBGMap0Address
+	pop hl
+	ld b, 1
+	call HblankCopyDataHLtoDE
+	pop bc
+	pop de
+	pop hl
+	ret
+
+; copy a bytes of data from hl to vBGMap0 address pointed to by coord at bc
+CopyDataToBGMap0:
+	push bc
+	push hl
+	push af
+	call BCCoordToBGMap0Address
+	pop af
+	ld b, a
+	pop hl
+	call SafeCopyDataHLtoDE
+	pop bc
+	ret
+
+; copy b bytes of data from hl to de
+; if LCD on, copy during h-blank only
+SafeCopyDataHLtoDE: ; 6fc (0:6fc)
+	ld a, [wLCDC]
+	rla
+	jr c, JPHblankCopyDataHLtoDE
+.lcd_off_loop
+	ld a, [hli]
+	ld [de], a
+	inc de
+	dec b
+	jr nz, .lcd_off_loop
+	ret
+JPHblankCopyDataHLtoDE:
+	jp HblankCopyDataHLtoDE