/// <inheritdoc/>
protected override void Dispose(bool disposing)
{
if (this.isDisposed)
{
return;
}
if (disposing)
{
// dispose managed resources
this.deflateStream.Dispose();
// Add the crc
uint crc = (uint)this.adler32.Value;
this.rawStream.WriteByte((byte)((crc >> 24) & 0xFF));
this.rawStream.WriteByte((byte)((crc >> 16) & 0xFF));
this.rawStream.WriteByte((byte)((crc >> 8) & 0xFF));
this.rawStream.WriteByte((byte)(crc & 0xFF));
}
this.deflateStream = null;
base.Dispose(disposing);
this.isDisposed = true;
}
/// <summary>
/// Initializes a new instance of the <see cref="ZlibDeflateStream"/> class.
/// </summary>
/// <param name="memoryAllocator">The memory allocator to use for buffer allocations.</param>
/// <param name="stream">The stream to compress.</param>
/// <param name="level">The compression level.</param>
public ZlibDeflateStream(MemoryAllocator memoryAllocator, Stream stream, PngCompressionLevel level)
{
int compressionLevel = (int)level;
this.rawStream = stream;
// Write the zlib header : http://tools.ietf.org/html/rfc1950
// CMF(Compression Method and flags)
// This byte is divided into a 4 - bit compression method and a
// 4-bit information field depending on the compression method.
// bits 0 to 3 CM Compression method
// bits 4 to 7 CINFO Compression info
//
// 0 1
// +---+---+
// |CMF|FLG|
// +---+---+
const int Cmf = 0x78;
int flg = 218;
// http://stackoverflow.com/a/2331025/277304
if (compressionLevel >= 5 && compressionLevel <= 6)
{
flg = 156;
}
else if (compressionLevel >= 3 && compressionLevel <= 4)
{
flg = 94;
}
else if (compressionLevel <= 2)
{
flg = 1;
}
// Just in case
flg -= ((Cmf * 256) + flg) % 31;
if (flg < 0)
{
flg += 31;
}
this.rawStream.WriteByte(Cmf);
this.rawStream.WriteByte((byte)flg);
this.deflateStream = new DeflaterOutputStream(memoryAllocator, this.rawStream, compressionLevel);
}