// 从协议中获取字符串内容
public String GetString()
{
if (bytes == null)
{
return("");
}
if (bytes.Length < start + 4)
{
return("");
}
// 获得协议中字符串的长度
int strLen = MyBitConverter.ToInt32(bytes, start);
if (bytes.Length < start + 4 + strLen)
{
return("");
}
// 获得协议中具体的字符串的内容
String str = System.Text.Encoding.UTF8.GetString(bytes, start + sizeof(Int32), strLen);
// start指针前移
this.start = start + 4 + strLen;
return(str);
}
/// <summary>
/// Reads a PNG header chunk.
/// </summary>
/// <param name="headerBlock">Block of data containing headers.</param>
/// <param name="offset">Offset in data to begin header.</param>
public PNGChunk(byte[] headerBlock, int offset = 8)
{
Length = MyBitConverter.ToInt32(headerBlock, offset, MyBitConverter.Endianness.BigEndian);
ChunkType = MyBitConverter.ToInt32(headerBlock, offset + 4, MyBitConverter.Endianness.BigEndian);
ChunkData = new byte[Length];
Array.Copy(headerBlock, offset + 8, ChunkData, 0, Length);
CRC = MyBitConverter.ToInt32(headerBlock, offset + 8 + Length, MyBitConverter.Endianness.BigEndian);
}
public int GetInt()
{
if (bytes == null)
{
return(0);
}
if (bytes.Length < start + 4)
{
return(0);
}
int result = MyBitConverter.ToInt32(bytes, start);
start = start + 4;
return(result);
}
/// <summary>
/// Read field descriptor from block.
/// A "property" of the image.
/// </summary>
/// <param name="IDBlock">Block containing descriptor, but NOT it's data.</param>
/// <param name="endianness">Big or little endianness defined by TIFF header.</param>
/// <param name="dataStream">Full image stream to read descriptor data from.</param>
public FieldDescriptor(byte[] IDBlock, MyBitConverter.Endianness endianness, Stream dataStream)
{
FieldTag = (FieldTags)MyBitConverter.ToInt16(IDBlock, 0, endianness);
FieldType = (FieldTypes)MyBitConverter.ToInt16(IDBlock, 2, endianness);
FieldLength = MyBitConverter.ToInt32(IDBlock, 4, endianness);
DataOffset = MyBitConverter.ToInt32(IDBlock, 8, endianness);
// Read data indicated by descriptor
long oldOffset = dataStream.Position;
dataStream.Seek(DataOffset, SeekOrigin.Begin);
Data = new byte[FieldLength];
dataStream.Read(Data, 0, FieldLength);
// Reset stream position for next descriptor
dataStream.Seek(oldOffset, SeekOrigin.Begin);
}
/// <summary>
/// Loads PNG header from stream.
/// </summary>
/// <param name="stream">Fully formatted header stream. Position not relevant, but not reset.</param>
/// <returns>Header length.</returns>
protected override long Load(Stream stream)
{
base.Load(stream);
byte[] temp = stream.ReadBytes(HeaderSize);
if (!CheckIdentifier(temp))
{
throw new FormatException("Stream is not a PNG Image");
}
PNGChunk header = new PNGChunk(temp);
Width = MyBitConverter.ToInt32(header.ChunkData, 0, MyBitConverter.Endianness.BigEndian);
Height = MyBitConverter.ToInt32(header.ChunkData, 4, MyBitConverter.Endianness.BigEndian);
BitDepth = header.ChunkData[8];
colourType = (ColourType)header.ChunkData[9];
CompressionMethod = (CompressionMethods)header.ChunkData[10];
FilterMethod = (FilterMethods)header.ChunkData[11];
InterlaceMethod = (InterlaceMethdods)header.ChunkData[12];
return(-1); // Since we don't know the length of the entire header, no point returning any value.
}
