RISCBoy

#!/usr/bin/env python3

from PIL import Image
import argparse

def bytes_from_bitstream_le(bitstream):
	accum = 0
	accum_size = 0
	while True:
		while accum_size < 8:
			nbits, newdata = next(bitstream)
			accum = accum | (newdata << accum_size)
			accum_size += nbits
		while accum_size >= 8:
			yield accum & 0xff
			accum = accum >> 8
			accum_size -= 8

def format_pixel(format, src_has_transparency, pixel):
	assert(format in ["argb1555", "argb1232", "p8", "p4", "p2", "p1"])
	if format == "argb1555":
		return (16, ((pixel[2] & 0xf8) >> 3) | \
			((pixel[1] & 0xf8) << 2) | \
			((pixel[0] & 0xf8) << 7) | \
			(((pixel[3] & 0x80) << 8) if len(pixel) > 3 and src_has_transparency else 0x8000))
	elif format == "argb1232":
		return (8, ((pixel[2] & 0xc0) >> 6) |\
			((pixel[1] & 0xe0) >> 3) | \
			((pixel[0] & 0xc0) >> 1) | \
			(pixel[3] & 0x80 if len(pixel) > 3 and src_has_transparency else 0x80))
	elif format in ["p8", "p4", "p2", "p1"]:
		size = int(format[1:])
		return (size, (pixel + src_has_transparency) & ((1 << size) - 1))
	else:
		raise Exception()

if __name__ == "__main__":
	parser = argparse.ArgumentParser()
	parser.add_argument("input", help="Input file name")
	parser.add_argument("output", help="Output file name")
	parser.add_argument("--tilesize", "-t", help="Tile size (pixels), default 8",
		default="8", choices=["8", "16"])
	parser.add_argument("--format", "-f", help="Output pixel format, default argb1555",
		default="argb1555", choices=["argb1555", "argb1232", "p8", "p4", "p2", "p1"])
	args = parser.parse_args()
	img = Image.open(args.input)
	ofile = open(args.output, "wb")
	tilesize = int(args.tilesize)

	format_is_paletted = args.format.startswith("p")
	image_is_transparent = img.mode == "RGBA" and img.getextrema()[3][0] < 255

	if format_is_paletted:
		ncolours_max = 1 << int(args.format[1:])
		ncolours_actual = min(ncolours_max, len(img.getcolors()))
		pimg = img.quantize(ncolours_max)
		palette = pimg.getpalette()
		# TODO haven't found a sane way to make PIL map transparency to palette
		if image_is_transparent:
			for x in range(img.width):
				for y in range(img.height):
					if not (img.getpixel((x, y))[3] & 0x80):
						pimg.putpixel((x, y), 255)

		with open(args.output + ".pal", "wb") as pfile:
			if image_is_transparent:
				pfile.write(bytes(2))
			pfile.write(bytes(bytes_from_bitstream_le(
				format_pixel("argb1555", False, palette[i:i+3]) for i in range(0, ncolours_actual * 3, 3)
			)))
		img = pimg

	for y in range(0, img.height - (tilesize - 1), tilesize):
		for x in range(0, img.width - (tilesize - 1), tilesize):
			tile = img.crop((x, y, x + tilesize, y + tilesize))
			ofile.write(bytes(bytes_from_bitstream_le(
				format_pixel(args.format, image_is_transparent, tile.getpixel((i, j))) for j in range(tilesize) for i in range(tilesize)
			)))