public async Task ParseAsync(Stream stream, bool skipTypeIdentifier = false, bool ignoreImageData = false)
{
if (stream != null)
{
GIFBitmap previousBitmap = null;
GIFBitmap currentBitmap = null;
GIFBitmapDecoder decoder = new GIFBitmapDecoder();
GIFDecoderStreamReader reader = new GIFDecoderStreamReader(stream);
StartParsing();
GIFHeader header = await GIFHeader.CreateHeaderAsync(reader, skipTypeIdentifier).ConfigureAwait(false);
currentBitmap = await GIFBitmap.CreateBitmapAsync(reader, header, decoder, previousBitmap, ignoreImageData).ConfigureAwait(false);
while (currentBitmap != null)
{
AddBitmap(header, currentBitmap, ignoreImageData);
previousBitmap = currentBitmap;
currentBitmap = await GIFBitmap.CreateBitmapAsync(reader, header, decoder, previousBitmap, ignoreImageData).ConfigureAwait(false);
}
FinishedParsing();
}
else
{
throw new ArgumentNullException(nameof(stream));
}
}
async Task ParseImageDescriptorAsync(GIFDecoderStreamReader stream, GIFBitmapDecoder decoder, GIFBitmap previousBitmap, bool ignoreImageData)
{
await ParseGIFBitmapHeaderAsync(stream).ConfigureAwait(false);
if (IsTransparent)
{
ColorTable.SetTransparency(TransparencyIndex);
}
DataPosition = stream.CurrentPosition;
if (!ignoreImageData)
{
// Decode LZW data stream.
await decoder.DecodeAsync(stream, _header.Width, _header.Height).ConfigureAwait(false);
// Compose bitmap from decoded data stream.
decoder.Compose(_header, this, previousBitmap);
// Consume block terminator.
await stream.SkipBlockAsync().ConfigureAwait(false);
}
else
{
// Read pass variable length LZW data stream.
// First byte is LZW code size followed by data blocks repeated until block terminator.
stream.Read();
await stream.SkipBlockAsync().ConfigureAwait(false);
}
if (IsTransparent)
{
ColorTable.ResetTransparency();
}
}
public static async Task <GIFBitmap> CreateBitmapAsync(GIFDecoderStreamReader stream, GIFHeader header, GIFBitmapDecoder decoder, GIFBitmap previousBitmap, bool ignoreImageData = false)
{
GIFBitmap currentBitmap = null;
bool haveImage = false;
bool done = false;
while (!done)
{
int blockCode = stream.Read();
if (blockCode == -1)
{
currentBitmap = null;
break;
}
switch (blockCode)
{
case GIFBlockCodes.ImageSeparator:
if (currentBitmap == null)
{
currentBitmap = new GIFBitmap(header);
}
await currentBitmap.ParseImageDescriptorAsync(stream, decoder, previousBitmap, ignoreImageData).ConfigureAwait(false);
haveImage = true;
done = true;
break;
case GIFBlockCodes.Extension:
if (currentBitmap == null)
{
currentBitmap = new GIFBitmap(header);
}
await currentBitmap.ParseExtensionAsync(stream).ConfigureAwait(false);
break;
case GIFBlockCodes.Trailer:
done = true;
if (!haveImage)
{
currentBitmap = null;
}
break;
default:
break;
}
}
return(currentBitmap);
}
