Extract sprites type 6 in TWG

extract_sprite_6.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):
    buf = f.read(3)
    buf = struct.unpack('<BBB', buf)
    pal.append((buf[0], buf[1], buf[2]))

# extract sprites
with open(args.spr, 'rb') as f:
  f.seek(0, os.SEEK_END)
  file_len = f.tell()
  f.seek(0, os.SEEK_SET)

  # header
  f.seek(0x42, os.SEEK_SET)

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

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

  for n in range(num):
    buf = f.read(4)
    buf = struct.unpack('<I', buf)
    length = buf[0]
    
    # width
    buf = f.read(2)
    buf = struct.unpack('<H', buf)
    width = buf[0]
    assert MONITOR_WIDTH >= width
    
    # height
    buf = f.read(2)
    buf = struct.unpack('<H', buf)
    height = buf[0]
    assert MONITOR_HEIGHT >= height

    assert (4 + width * height) == length    
    
    # unknown
    f.seek(2, os.SEEK_CUR)
    f.seek(2, os.SEEK_CUR)

    buf = f.read(2)
    buf = struct.unpack('<H', buf)
    assert buf[0] == width

    buf = f.read(2)
    buf = struct.unpack('<H', buf)
    assert buf[0] == height

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

    # draw a sprite on monitor
    for idx in range(width * height):
      assert f.tell() < file_len

      buf = f.read(1)
      buf = struct.unpack('<B', buf)
      pal_idx = buf[0]
      if 0xff != pal_idx: # maybe, 0xff means 'Not painted'.
        monitor[idx] = pal[pal_idx]

    # 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[width * h + w]
          out.write('%d %d %d\n' % (rgb[0], rgb[1], rgb[2]))

  assert f.tell() == file_len