wad3texture_to_gif.py

import sys
import argparse

def vlc_lzw_compress(data, nbit=8):
    assert 1 < nbit < 9, 'nbit must satisfies, 1 < nbit < 9'
        
    # LZW encoding
    CLR = 1<<nbit
    END = CLR+1
    d = {}
    n = nbit+1
    x = END+1
    y = 1 << n
    O = [(CLR, n)]
    k = (data[0],)
    for i in data[1:]:
        k = (k[0],i)
        if k in d:
            k = (d[k],)
        else:
            d[k] = x
            O.append((k[0], n))
            if x == y:
                n += 1
                y <<= 1
            x += 1
            if x == 0x1000:
                O.append((CLR, n))
                d = {}
                n = nbit+1
                x = END+1
                y = 1 << n
            k = (k[1],)
    O.append((k[0], n))
    O.append((END, n))

    # 8-bit string encoding
    b = bytearray()
    x = 0
    y = 0
    for i, j in O:
        x |= (i << y)
        y += j
        while y >= 8:
            b.append(x & 0xff)
            x >>= 8
            y -= 8

    if y:
        b.append(x)

    return bytes(b)

def main():
    usage = '''wad3texture_to_gif < gif > wad'''
    parser = argparse.ArgumentParser(usage=usage)
    args = parser.parse_args()

    # read wad file
    wad = sys.stdin.buffer.read()

    # parsing wad and get texture
    num_dirs = int.from_bytes(wad[0x4:0xc], 'little')
    dir_offset = int.from_bytes(wad[0x8:0xc], 'little')

    o = dir_offset
    entry_offset = int.from_bytes(wad[o+0:o+4], 'little')
    disk_size = int.from_bytes(wad[o+4:o+8], 'little')
    o0 = entry_offset
    o1 = o0 + disk_size
    entry = wad[o0:o1]

    width = int.from_bytes(entry[0x10:0x14], 'little')
    height = int.from_bytes(entry[0x14:0x18], 'little')
    mip0_offset = int.from_bytes(entry[0x18:0x1c], 'little')

    o0 = mip0_offset
    o1 = o0 + width * height
    mip0 = entry[o0:o1]

    mip4_offset = int.from_bytes(entry[0x24:0x28], 'little')
    o = mip4_offset + width * height // 64
    colors_used = int.from_bytes(entry[o:o+2], 'little')

    o0 = mip4_offset + width * height // 64 + 0x2
    o1 = o0 + colors_used * 3
    pallet = entry[o0:o1]

    mip0_compressed = vlc_lzw_compress(mip0)
    #width = height = 3
    #mip0_compressed = vlc_lzw_compress(b'\x00\x00\x00\xff\x00\xff\xff\x00\xff')

    b = (
         # Header

         # Magic
         b'GIF'
         # Version
         + b'89a'
         # Logical Screen Width
         + width.to_bytes(2, 'little')
         # Logical Screen Height
         + height.to_bytes(2, 'little')
         # Global Color Table Flag = true
         # Color Resolution = 7
         # Sort Flag = false
         # Size of Global Color Table = 0
         + b'\xf7'
         # Background Color Index
         + b'\xff'
         # Pixel Aspect Ratio
         + b'\x00'
         # Global Color Table
         + pallet

         # Graphic Control Extension

         # Extension Introducer
         + b'\x21'
         # Graphic Control Label
         + b'\xf9'
         # Block Size
         + b'\x04'
         # Reserved = 0
         # Disposal Method = 0
         # User Input Flag = false
         # Transparent Color Flag = true
         + b'\x01'
         # Delay Time
         + b'\x00\x00'
         # Transparent Color Index
         + b'\xff'
         # Block Terminator
         + b'\x00'

         # Image Descriptor

         # Image Separator
         + b'\x2c'
         # Image Left Position
         + b'\x00\x00'
         # Image Top Position
         + b'\x00\x00'
         # Image Width
         + width.to_bytes(2, 'little')
         # Image Height
         + height.to_bytes(2, 'little')
         # Local Color Table Flag = true
         # Interlace Flag = false
         # Sort Flag = false
         # Reserved = 0
         # Size of Local Color Table = 0
         + b'\x00'
         # Local Color Table
         + b''
         # LZW Minimum Code Size
         + b'\x08'
         + b''.join(
             # Block Size
             len(mip0_compressed[i:i+0xff]).to_bytes(1)
             # Image Data
             + mip0_compressed[i:i+0xff]
             for i in range(0, len(mip0_compressed), 0xff)
         )

         # Block Terminator
         + b'\x00'

         # Trailer
         + b'\x3b')

    # write gif file
    sys.stdout.buffer.write(b)

if __name__ == '__main__':
    main()