ChocolateBird/scripts/loaders/snes/battle_bgs.gd

const NUM_COLUMNS := 32
const NUM_ROWS := 20
const LENGTH := NUM_COLUMNS * NUM_ROWS  # 0x500 / 2  # Expanded length 0x500, RLE step produces 0x280 tile mappings
const NUM_BATTLE_BG_TILESETS := 21  # These combine with a RAM skip amount to form a subset used as a tile atlas
const NUM_BATTLE_BG_TILEMAPS := 28
const NUM_BATTLE_BG_FLIPSETS := 9
const IMAGE_FORMAT := Image.FORMAT_LA8
const compression = preload('res://scripts/loaders/snes/compression.gd')


class TileMapping:
	var tile_index: int
	var palette: int
	var priority: bool
	var h_flip: bool
	var v_flip: bool

	static func from_tilemap_word(w: int) -> TileMapping:
		var t := TileMapping.new()
		t.tile_index = w & 0x03FF
		t.palette = (w & 0x1C00) >> 10
		t.priority = bool(w & 0x2000)
		t.h_flip = bool(w & 0x4000)
		t.v_flip = bool(w & 0x8000)
		return t

	static func from_battle_byte(b: int) -> TileMapping:
		var t := TileMapping.new()
		t.tile_index = b & 0x7F  # In-game this gets |= 0x80, as the BG tiles are from 0x80 to 0xFF
		t.palette = b >> 7  # In-game this gets incremented by 1, as the BG palettes are #1 and #2 leaving #0 for UI elements
		return t

	func serialize(buffer: StreamPeer) -> void:
		# 8bit for tile_index
		# 6bit for palette
		# 1bit for each flip
		# Do nothing with priority, should have two textures for each layer depending on it
		buffer.put_u8(self.tile_index)
		var byte2 := self.palette
		if self.h_flip:
			byte2 += 0x40
		if self.v_flip:
			byte2 += 0x80
		buffer.put_u8(byte2)


static func decompress_battle_tilemap(buffer: StreamPeer) -> Array:
	# Decompresses the tilemap for a battle background.
	# Battle BGs use a type of RLE with 2byte repeat and 1byte incremental repeat.
	var mappings := []
	while len(mappings) < LENGTH:
		var byte := buffer.get_u8()
		if byte != 0xFF:
			mappings.append(TileMapping.from_battle_byte(byte))
		else:  # Byte begins a repeat code
			var repeat_code := buffer.get_u8()
			var repeat := repeat_code & 0x3F
			byte = buffer.get_u8()
			if repeat_code & 0x80:  # Repeat 2 tiles
				var byte2 := buffer.get_u8()
				for i in repeat:
					mappings.append(TileMapping.from_battle_byte(byte))
					mappings.append(TileMapping.from_battle_byte(byte2))
			else:  # Incremental repeat
				var inc := buffer.get_u8()
				if repeat_code & 0x40:  # Negative increment
					inc = -inc
				for i in repeat:
					mappings.append(TileMapping.from_battle_byte(byte))
					byte += inc
	return mappings

static func apply_battle_tilemap_flips(buffer: StreamPeer, tilemap: Array):
	var tile_i := 0
	while tile_i < LENGTH:
		var a := buffer.get_u8()
		if a == 0x00: # Skip N*8 tiles
			tile_i += buffer.get_u8() * 8
		else:
			# Each bit is a tile, 1 means flip horizontally
			for b in range(7, -1, -1):
				tilemap[tile_i].h_flip = bool((a>>b) & 0x01)
				tile_i += 1

static func add_anim_palettes(buffer: StreamPeer, palettes: Array):
	# TODO: check if the very first entry is added too
	var pal1_id: int = palettes[0][0]
	var pal2_id: int = palettes[0][1]
	while true:
		var b := buffer.get_u8()
		if b == 0xFF:
			break
		if b & 0x80:
			pal2_id = b & 0x7F
		else:
			pal1_id = b
		palettes.append([pal1_id, pal2_id])

static func get_anim_tiles(buffer: StreamPeer) -> Array:
	var output := []
	while true:
		var b := buffer.get_u8()  # 2 MSb frame number (0-3), 6 bit tile index to replace
		var b2 := buffer.get_u8()  # tile index to copy from
		if (b == 0xFF) or (b2 == 0xFF):
			break
		output.append([b, b2])
	return output

static func array_of_tilemappings_to_image(tilemappings: Array) -> Image:
	var out := Image.new()
	var buffer := StreamPeerBuffer.new()
	for tilemapping in tilemappings:
		tilemapping.serialize(buffer)
	out.create_from_data(NUM_COLUMNS, NUM_ROWS, false, IMAGE_FORMAT, buffer.data_array)
	return out

static func get_all_battle_background_tilesets(buffer: StreamPeer, tileset_offsets: Array, skip_offsets: Array) -> Array:
	# Convert these to 4bpp tiles to create your atlases
	var raw_tilesets := {}  # key is offset, value is decompressed tiles
	var tilesets := []
	for i in NUM_BATTLE_BG_TILESETS:
		var skip: int = skip_offsets[i] - 0x7FC000
		var offset: int = tileset_offsets[i] - 0xC00000
		if not (offset in raw_tilesets):
			buffer.seek(offset)
			raw_tilesets[offset] = compression.decompress_lzss(buffer)
		var raw: PoolByteArray = raw_tilesets[offset]
		var skipped_raw := raw.subarray(skip, -1)
		tilesets.append(skipped_raw)
	return tilesets

static func get_all_battle_background_tilemaps(buffer: StreamPeerBuffer, data: Dictionary) -> Array:
	var tbl_battle_backgrounds: Array = data.tbl_battle_backgrounds
	var tilesets = get_all_battle_background_tilesets(buffer, data.ptrs_battle_background_tilesets, data.ptrs_battle_background_tileset_skips)

	var tilemaps = []
	for i in NUM_BATTLE_BG_TILEMAPS:
		buffer.seek(data.ptrs_battle_background_tilemaps[i] + 0x140000)
		tilemaps.append(decompress_battle_tilemap(buffer))

	var output := []
	for tbl in tbl_battle_backgrounds:
		var out := {}
		out.tileset = tilesets[tbl.tileset_id]
		out.palette_ids = [tbl.palette_ids]
		var tilemap = tilemaps[tbl.tilemap_id]
		if tbl.tilemap_flips_id < NUM_BATTLE_BG_FLIPSETS:  # 0xFF means no flips
			buffer.seek(data.ptrs_battle_background_tilemap_flips[tbl.tilemap_flips_id] + 0x140000)
			apply_battle_tilemap_flips(buffer, tilemap)
		out.tilemap_image = array_of_tilemappings_to_image(tilemap)
		if tbl.palcycle_id < 0xFF:
			buffer.seek(data.ptrs_battle_background_palette_animations[tbl.palcycle_id] + 0x140000)
			add_anim_palettes(buffer, out.palette_ids)
		if tbl.tilecycle_id > 0:
			buffer.seek(data.ptrs_battle_background_tile_animations[tbl.tilecycle_id] + 0x140000)
			out.animated_tiles = get_anim_tiles(buffer)
		output.append(out)

	return output