/// <summary>
/// Gets the most specific <see cref="GifExtension"/>-derivate from the byte representation starting from the current position in the <see cref="Stream"/>.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing the byte representation of a <see cref="GifExtension"/>.</param>
/// <returns>A most specific <see cref="GifExtension"/>-derivate corresponding to the byte representation.</returns>
internal static GifExtension FromStream(Stream stream)
{
if (stream.ReadByte() != header)
{
throw new FormatException("Stream has to have an Extension coming up!");
}
var functionCode = (byte)stream.ReadByte();
var data = GifDataStream.Decode(stream);
var extension = getSpecificExtension.ContainsKey(functionCode) ?
getSpecificExtension[functionCode](data) : new GenericGifExtension(data);
extension.FunctionCode = functionCode;
return(extension);
}
/// <summary>
/// Gets the decompressed Color Data starting from the current position in the <see cref="Stream"/>.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing the compressed Color Data.</param>
/// <returns>The decompressed Color Data.</returns>
public static byte[] Decode(Stream stream)
{
var startCodeSize = (byte)stream.ReadByte();
if (startCodeSize < minStartCodeSize || startCodeSize > maxStartCodeSize)
{
throw new ArgumentOutOfRangeException("startCodeSize", "The encoded start code size has to be between 2 and 8!");
}
var indexStream = new List <byte>();
var codeData = GifDataStream.Decode(stream);
using (var codeStream = new BitStream.BitStream(new MemoryStream(codeData)))
{
var codeTable = new List <CodeTableEntry>();
buildCodeTable(codeTable, startCodeSize);
var codeSize = startCodeSize + 1u;
var indexBuffer = new List <byte>();
CodeTableEntry codeEntry;
ushort prevCode = getColorCodeCount(startCodeSize);
var first = true;
do
{
var codeBytes = new byte[2];
codeStream.ReadBits(codeBytes, 0, codeSize);
var code = BitConverter.ToUInt16(codeBytes, 0);
if (code < codeTable.Count)
{
codeEntry = codeTable[code];
if (codeEntry == CodeTableEntry.Clear)
{
indexBuffer.Clear();
buildCodeTable(codeTable, startCodeSize);
first = true;
}
else if (codeEntry != CodeTableEntry.EndOfInformation)
{
indexStream.AddRange(codeTable[code].Colors);
if (!first)
{
indexBuffer.Clear();
indexBuffer.AddRange(codeTable[prevCode].Colors);
indexBuffer.Add(codeTable[code].Colors[0]);
codeTable.Add(CodeTableEntry.MakeColorEntry(indexBuffer.ToArray()));
}
first = false;
}
}
else if (code == codeTable.Count)
{
indexBuffer.Clear();
indexBuffer.AddRange(codeTable[prevCode].Colors);
indexBuffer.Add(codeTable[prevCode].Colors[0]);
codeEntry = CodeTableEntry.MakeColorEntry(indexBuffer.ToArray());
codeTable.Add(codeEntry);
indexStream.AddRange(codeTable[code].Colors);
}
else
{
throw new ArgumentOutOfRangeException("code", "Encoded code was too large. Expected: " + codeTable.Count + " or less; got: " + code);
}
if (Math.Pow(2, codeSize) <= codeTable.Count)
{
++codeSize;
}
prevCode = code;
}while (codeEntry != CodeTableEntry.EndOfInformation);
}
return(indexStream.ToArray());
}
