This is both kind-of on and off topic... I plan to investigate what kind of data I can extract from Panzer Dragoon Saga, and one of the few Sega-internal formats is PRS. I found a closed-source decompressor, and a few open-source (in cpp and c#) that seemed to be unnecessarily complicated. I implemented this routine in python so that other people have a better reference, and I can investigate Saga. I compared the output on NiGHTS with the closed-source decompressor, and the result is identical.
Unfortunately I don't have a model or texture viewer, yet.
(On-topic because the algorithm is based on LZS similar to Xenogears and FF7, so maybe useful if this extension was picked up by square.)
# SEGA PRS Decompression (LZS variant)
# Credits:
# based on information/comparing output with
# Nemesis/http://www.romhacking.net/utils/671/
# puyotools/http://code.google.com/p/puyotools/
# fuzziqer software prs/http://www.fuzziqersoftware.com/projects.php
import array
class DecompressPrs:
def __init__(self, data):
self.ibuf = array.array("B", data)
self.obuf = array.array("B")
self.iofs = 0
self.bit = 0
self.cmd = 0
def getByte(self):
val = self.ibuf[self.iofs]
self.iofs += 1
return val
def getBit(self):
if self.bit == 0:
self.cmd = self.getByte()
self.bit = 8
bit = self.cmd & 1
self.cmd >>= 1
self.bit -= 1
return bit
def decompress(self):
while self.iofs < len(self.ibuf):
cmd = self.getBit()
if cmd:
self.obuf.append(self.ibuf[self.iofs])
self.iofs += 1
else:
t = self.getBit()
if t:
a = self.getByte()
b = self.getByte()
offset = ((b << 8) | a) >> 3
amount = a & 7
if self.iofs < len(self.ibuf):
if amount == 0:
amount = self.getByte() + 1
else:
amount += 2
start = len(self.obuf) - 0x2000 + offset
else:
amount = 0
for j in xrange(2):
amount <<= 1
amount |= self.getBit()
offset = self.getByte()
amount += 2
start = len(self.obuf) - 0x100 + offset
for j in xrange(amount):
if start < 0:
self.obuf.append(0)
elif start < len(self.obuf):
self.obuf.append(self.obuf[start])
else:
self.obuf.append(0)
start += 1
return self.obuf.tostring()
def main():
import glob, os
list = glob.glob("NiGHTS/*.PRS")
for file in list:
f = open(file, "rb")
data = f.read()
f.close()
prs = DecompressPrs(data)
data = prs.decompress()
outfile = os.path.splitext(file)[0] + ".bin"
f = open(outfile, "wb")
f.write(data)
f.close()
if __name__ == "__main__":
main()
No fancy user interface, you'll have to fix the path to your data in the main routine, or integrate it into your own framework.
