Extract sprite type 1 in TWG

extract_sprite_1.py

# -*- coding: utf-8 -*-

# Extract sprites

import argparse
import struct
import os

# mode 13h resolution
MONITOR_WIDTH = 320
MONITOR_HEIGHT = 200
# bright pink
SPRITE_BACKGROUND = (255, 0, 255)

parser = argparse.ArgumentParser(description='Extract sprites.')
parser.add_argument('-p', required=True, help='palette file', dest='pal')
parser.add_argument('-f', required=True, help='compressed sprites file',
                    dest='spr')
args = parser.parse_args()

# read palette
pal = []
with open(args.pal, 'rb') as f:
  for i in range(256):
    bytes = f.read(3)
    bytes = struct.unpack('<BBB', bytes)
    pal.append((bytes[0], bytes[1], bytes[2]))

# extract sprites
with open(args.spr, 'rb') as f:
  # header
  f.seek(0x42, os.SEEK_SET)

  # total number of sprites
  bytes = f.read(2)
  bytes = struct.unpack('<H', bytes)
  num = bytes[0]

  # zero padding
  f.seek(60, os.SEEK_CUR)

  offsets = []
  for n in range(num):
    bytes = f.read(4)
    bytes = struct.unpack('<I', bytes)
    offsets.append(bytes[0])

  n = 0
  for ofs in offsets:
    f.seek(ofs, os.SEEK_SET)

    # length of compressed pixel data
    bytes = f.read(4)
    bytes = struct.unpack('<I', bytes)
    len = bytes[0]

    # width
    bytes = f.read(2)
    bytes = struct.unpack('<H', bytes)
    width = bytes[0]
    assert 320 >= width

    # height
    bytes = f.read(2)
    bytes = struct.unpack('<H', bytes)
    height = bytes[0]
    assert 200 >= height

    # unknown
    f.seek(2, os.SEEK_CUR)
    f.seek(2, os.SEEK_CUR)

    # number of compressed chunks
    bytes = f.read(2)
    bytes = struct.unpack('<H', bytes)
    chunks = bytes[0]

    # reset monitor
    monitor = []
    for i in range(MONITOR_WIDTH * MONITOR_HEIGHT):
      monitor.append(SPRITE_BACKGROUND)

    # draw a sprite on monitor
    idx = 0
    for c in range(chunks):
      bytes = f.read(2)
      bytes = struct.unpack('<H', bytes)
      blanks = bytes[0]
      idx = idx + blanks

      bytes = f.read(1)
      bytes = struct.unpack('<B', bytes)
      drawn = 4 * bytes[0]

      bytes = f.read(1)
      bytes = struct.unpack('<B', bytes)
      drawn = drawn + bytes[0]
    
      for d in range(drawn):
        bytes = f.read(1)
        bytes = struct.unpack('<B', bytes)
        pal_idx = bytes[0]
        monitor[idx] = pal[pal_idx]
        idx = idx + 1

    # write a sprite to file
    out_name = os.path.basename(args.spr)
    out_name = out_name + '.%05d' % n + '.ppm'

    with open(out_name, 'w') as out:
      out.write('P3\n')
      out.write('%d %d\n' % (width, height))
      out.write('255\n')
      
      for h in range(height):
        for w in range(width):
          rgb = monitor[320 * h + w]
          out.write('%d %d %d\n' % (rgb[0], rgb[1], rgb[2]))

    n = n + 1