Convert PaintWorks Animation (Apple IIgs $C2 filetype) to Animated GIF

c2-to-animgif.py

# Example: python c2-to-animgif.py anim.c2 outputname.gif
from PIL import Image,ImageDraw 		# `pip3 install pillow==7.0.0` if you don't have it
from sys import argv, stdout
import glob, tempfile, struct, os

def get_scanline_palette(scanline):
    scb = shr_buffer[0x7D00+scanline]   # SCBs start at $E19D00 (SHR RAM starts offset +$2000)
    cur_pal_num = scb & 0x0F
    pal_offset = 0x7E00+(cur_pal_num*16*2) # each pal is 16 colors * 2 bytes per color
    # now make a dict of each index => (r,g,b) tuple
    result = {}
    for i in range(0,16):
        g = shr_buffer[pal_offset+(i*2)] >> 4 & 0x0F
        b = shr_buffer[pal_offset+(i*2)] & 0x0F
        r = shr_buffer[pal_offset+(i*2)+1]

        # expand to 24-bit color colorspace for png/rgb
        r += (r*16)
        g += (g*16)
        b += (b*16)
        result[i] = (r,g,b)
    return result

def return_frame():
    # Create new indexed (P) image
    img = Image.new('P', (320, 200), color = 'red')
    d = ImageDraw.Draw(img)

    # foreach scanline
    for y in range(0,200):
        # get scanline palette (as dict k=>(r,g,b))
        curPal = get_scanline_palette(y)
        # foreach byte (2 pixels)
        for x in range(0,160): # 320/2=160 because 2 pixels per byte = 160 bytes per scanline row
            data = shr_buffer[(y*160)+x]
            px1 = data >> 4
            px2 = data & 0x0F
            d.point((x*2,y),curPal[px1])
            d.point(((x*2)+1,y),curPal[px2])
    return img

def get_long():
    result = get_word() + (get_word() << 16)    # get two words ;) 
    return result

def get_word():
    global decode_stream_ptr
    result = c2_buffer[decode_stream_ptr] + \
             (c2_buffer[decode_stream_ptr+1] << 8)
    decode_stream_ptr += 2
    return result

def decode_next_frame():
    global shr_buffer
    zero_offset = False
    while not zero_offset:
        offset = get_word()
        if offset == 0:
            zero_offset = True
            get_word()
            continue
        value = get_word()
        shr_buffer[offset] = value & 0xFF
        shr_buffer[offset+1] = value >> 8
    return True


# READ PAINTWORKS ANIMATION FILE
c2_buffer = bytearray(open(argv[1], "rb").read())
# INITIALIZE
tickscaler = 19 # this scales the delay in output gif; 19 seems close to Platinum Paint delay
decode_stream_ptr = 0x8000
animdata_len = get_long()
tickcount = get_word()
decode_stream_ptr = 0x800C # Skip to anim frames now
finished = False
outfile = argv[2]
shr_buffer = c2_buffer[0:0x8000] # first $8000 is just raw frame to put in SHR RAM
frames = []
while decode_stream_ptr < len(c2_buffer):
    stdout.write(".") 
    stdout.flush()
    img = return_frame()
    frames.append(img)
    decode_next_frame()

print("\nSaving {} frames to {}".format(len(frames), outfile))
# Save into a GIF file that loops forever
frames[0].save(outfile, dither=None, append_images=frames[1:], save_all=True, duration=tickcount*tickscaler, loop=0)