public static void Decode(ByteStream data, Bitmap dest)
{
PNGHeader header = data.Struct <PNGHeader>(true);
Debug.Assert(header.Signature == PNGSignature, "Specified file was not a PNG file.");
ByteStream idatStream = new ByteStream();
while (true)
{
PNGChunkHeader chunkHeader = data.Struct <PNGChunkHeader>(true);
string chunkType = Encoding.ASCII.GetString(chunkHeader.Type, 4);
byte[] chunkBytes = data.Read(chunkHeader.Length);
ByteStream chunkData = new ByteStream(chunkBytes);
PNGChunkFooter chunkFooter = data.Struct <PNGChunkFooter>(true);
Debug.Assert(Crc32(chunkHeader.ToBytes().Concat(chunkBytes).ToArray(), 4) == chunkFooter.CRC, chunkType + " chunk's CRC mismatched!");
switch (chunkType)
{
case "IHDR":
PNGIHDR ihdr = chunkData.Struct <PNGIHDR>(true);
Debug.Assert(ihdr.BitDepth == 8 && ihdr.ColorType == 6 && ihdr.CompressionMethod == 0 &&
ihdr.FilterMethod == 0 && ihdr.InterlaceMethod == 0, "The specified PNG file uses an unsupported format.");
dest.Width = ihdr.Width;
dest.Height = ihdr.Height;
dest.Pixels = new byte[ihdr.Width * ihdr.Height * 4];
break;
case "IDAT":
idatStream.Write(chunkData.Read(chunkHeader.Length));
break;
case "IEND":
idatStream.Seek(0, SeekOrigin.Begin);
PNGIDATHeader idatHeader = idatStream.Struct <PNGIDATHeader>(true);
byte[] idatData;
PNGIDATFooter idatFooter;
using (MemoryStream target = new MemoryStream())
using (DeflateStream decompressionStream = new DeflateStream(idatStream, CompressionMode.Decompress)) {
decompressionStream.CopyTo(target);
idatData = target.ToArray();
idatStream.Seek(-4);
idatFooter = idatStream.Struct <PNGIDATFooter>(true);
}
Debug.Assert(idatFooter.CheckValue == Alder32(idatData), "IDAT chunk compression check value mismatch!");
int scanlineSize = dest.Width * 4;
for (int scanline = 0; scanline < dest.Height; scanline++)
{
int offset = scanline * scanlineSize;
Array.Copy(idatData, offset + scanline + 1, dest.Pixels, offset, scanlineSize);
}
return;
}
}
}
private static void WriteChunk(MemoryStream stream, string type, byte[] data)
{
PNGChunkHeader header = new PNGChunkHeader {
Length = data.Length,
};
for (int i = 0; i < 4; i++)
{
header.Type[i] = (byte)type[i];
}
PNGChunkFooter footer = new PNGChunkFooter {
CRC = Crc32(header.ToBytes().Concat(data).ToArray(), 4),
};
stream.Write(header.ToBytes(true));
stream.Write(data);
stream.Write(footer.ToBytes(true));
}