private GifFrame ReadImageData(BinaryReader reader)
{
var imageDescriptor = ImageDescriptor.Read(reader);
var localPalette = imageDescriptor.HasLocalPalette ? GifPalette.Read(reader, imageDescriptor.LocalPaletteColorCount) : null;
var lzwInitialCodeSize = reader.ReadByte() + 1;
var lzwBitReader = new GifLzwBitReader(new GifLzwByteReader(reader));
var lzwCodeSize = lzwInitialCodeSize;
var nextIncValue = (2 << (lzwCodeSize - 1)) - 1;
var decodeTable = new GifDecodeTable(_sreenDescriptor.GlobalPaletteColorCount);
int value;
#if SILVERLIGHT
var writeableBmp = new WriteableBitmap(_sreenDescriptor.Width, _sreenDescriptor.Height);
#else
var writeableBmp = new WriteableBitmap(_sreenDescriptor.Width, _sreenDescriptor.Height, 96.0, 96.0, PixelFormats.Bgra32, null);
#endif
var bmpWriter = new BmpWriter(writeableBmp, _globalPalette);
while (lzwBitReader.Read(lzwCodeSize, out value))
{
if (decodeTable.Count == nextIncValue)
{
lzwCodeSize++;
nextIncValue = (2 << (lzwCodeSize - 1)) - 1;
}
bool reset;
if (decodeTable.ProcessNextCode(value, bmpWriter, out reset) == false)
{
break;
}
if (reset)
{
lzwCodeSize = lzwInitialCodeSize;
nextIncValue = (2 << (lzwCodeSize - 1)) - 1;
}
if (lzwCodeSize > 12)
{
lzwCodeSize = 12;
}
}
bmpWriter.Flush();
return(new GifFrame(imageDescriptor, localPalette, writeableBmp));
}
public GifImageSource(Stream stream)
{
try
{
_gifStream = new MemoryStream();
stream.CopyTo(_gifStream);
_gifStream.Seek(0, SeekOrigin.Begin);
using (var reader = new BinaryReader(_gifStream))
{
var gifSign = new string(reader.ReadChars(6));
var gif89a = string.Equals(gifSign, "gif89a", StringComparison.OrdinalIgnoreCase);
var gif87a = string.Equals(gifSign, "gif87a", StringComparison.OrdinalIgnoreCase);
if ((gif87a || gif89a) == false)
{
return;
}
_sreenDescriptor = LogicalScreenDescriptor.Read(reader);
_globalPalette = _sreenDescriptor.HasGlobalPalette ? GifPalette.Read(reader, _sreenDescriptor.GlobalPaletteColorCount) : null;
while (true)
{
var ch = reader.ReadChar();
if (ch == ';' && reader.BaseStream.Position == reader.BaseStream.Length)
{
break;
}
switch (ch)
{
case '!':
SkipExtension(reader);
break;
case ',':
_frames.Add(ReadImage(reader));
break;
}
}
}
_isValid = true;
}
catch (Exception)
{
_isValid = false;
}
}