private static bool TryReadChunkHeader(Stream stream, out ChunkHeader chunkHeader)
{
chunkHeader = default;
var position = stream.Position;
if (!StreamHelper.TryReadHeaderBytes(stream, out var headerBytes))
{
return(false);
}
var length = StreamHelper.ReadBigEndianInt32(headerBytes, 0);
var name = Encoding.ASCII.GetString(headerBytes, 4, 4);
chunkHeader = new ChunkHeader(position, length, name);
return(true);
}
private static ImageHeader ReadImageHeader(Stream stream, byte[] crc)
{
if (!TryReadChunkHeader(stream, out var header))
{
throw new ArgumentException("The provided stream did not contain a single chunk.");
}
if (header.Name != "IHDR")
{
throw new ArgumentException($"The first chunk was not the IHDR chunk: {header}.");
}
if (header.Length != 13)
{
throw new ArgumentException($"The first chunk did not have a length of 13 bytes: {header}.");
}
var ihdrBytes = new byte[13];
var read = stream.Read(ihdrBytes, 0, ihdrBytes.Length);
if (read != 13)
{
throw new InvalidOperationException($"Did not read 13 bytes for the IHDR, only found: {read}.");
}
read = stream.Read(crc, 0, crc.Length);
if (read != 4)
{
throw new InvalidOperationException($"Did not read 4 bytes for the CRC, only found: {read}.");
}
var width = StreamHelper.ReadBigEndianInt32(ihdrBytes, 0);
var height = StreamHelper.ReadBigEndianInt32(ihdrBytes, 4);
var bitDepth = ihdrBytes[8];
var colorType = ihdrBytes[9];
var compressionMethod = ihdrBytes[10];
var filterMethod = ihdrBytes[11];
var interlaceMethod = ihdrBytes[12];
return(new ImageHeader(width, height, bitDepth, (ColorType)colorType, (CompressionMethod)compressionMethod, (FilterMethod)filterMethod,
(InterlaceMethod)interlaceMethod));
}
