IRandomGenerator DetectEncryptionScheme()
{
var first_entry = Dir.First();
int signature = (File.View.ReadInt32(first_entry.Offset) >> 8) & 0xFFFF;
byte seed = File.View.ReadByte(first_entry.Offset + first_entry.Size - 1);
IRandomGenerator[] rng_list =
{
new LehmerRandomGenerator(),
new CRuntimeRandomGenerator(),
};
foreach (var rng in rng_list)
{
rng.SRand(seed);
rng.Rand(); // skip LZSS control byte
int test = signature;
test ^= PakOpener.Key[rng.Rand() % PakOpener.Key.Length];
test ^= PakOpener.Key[rng.Rand() % PakOpener.Key.Length] << 8;
// FIXME
// as key is rather short, this detection could produce false results sometimes
if (0x4D42 == test) // 'BM'
{
return(rng);
}
}
throw new UnknownEncryptionScheme();
}
public byte[] ReadFrame(BdfFrame frame)
{
byte[] pixels;
if (!frame.Incremental)
{
if (null != FirstFrame && 0 == frame.Number)
{
return(FirstFrame);
}
pixels = new byte[frame.Width * frame.Height * 3];
using (var input = File.CreateStream(frame.Offset, frame.Size))
DecodeFrame(input, pixels);
if (null == FirstFrame && 0 == frame.Number)
{
FirstFrame = pixels;
}
}
else
{
if (null == FirstFrame)
{
var base_frame = Dir.First() as BdfFrame;
FirstFrame = new byte[base_frame.Width * base_frame.Height * 3];
using (var input = File.CreateStream(base_frame.Offset, base_frame.Size))
DecodeFrame(input, FirstFrame);
}
pixels = FirstFrame.Clone() as byte[];
int i = 1;
foreach (BdfFrame entry in Dir.Skip(1))
{
if (i++ > frame.Number)
{
break;
}
using (var input = File.CreateStream(entry.Offset, entry.Size))
DecodeFrame(input, pixels, entry.Incremental);
}
}
return(pixels);
}
