async Task ParseAsync(GIFDecoderStreamReader stream, bool skipTypeIdentifier)
{
if (!skipTypeIdentifier)
{
TypeIdentifier = stream.ReadString(3);
}
else
{
TypeIdentifier = "GIF";
}
if (IsGIFHeader)
{
Version = stream.ReadString(3);
Width = stream.ReadShort();
Height = stream.ReadShort();
int flags = stream.Read();
BackgroundColorIndex = stream.Read();
PixelAspectRatio = stream.Read();
if (UseGlobalColorTable(flags))
{
GlobalColorTable = await GIFColorTable.CreateColorTableAsync(stream, GlobalColorTableSize(flags)).ConfigureAwait(false);
BackgroundColor = GlobalColorTable.Data[BackgroundColorIndex];
}
}
else
{
throw new GIFDecoderFormatException("Unknown GIF format type identifier: " + TypeIdentifier);
}
}
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 <GIFColorTable> CreateColorTableAsync(GIFDecoderStreamReader stream, short size)
{
var colorTable = new GIFColorTable(size);
await colorTable.ParseAsync(stream).ConfigureAwait(false);
return(colorTable);
}
public static async Task <GIFHeader> CreateHeaderAsync(GIFDecoderStreamReader stream, bool skipTypeIdentifier = false)
{
GIFHeader header = new GIFHeader();
await header.ParseAsync(stream, skipTypeIdentifier).ConfigureAwait(false);
if (!header.IsGIFHeader)
{
header = null;
}
return(header);
}
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);
}
async Task ParseGIFBitmapHeaderAsync(GIFDecoderStreamReader stream)
{
Bounds = new GIFBitmap.Rect(stream.ReadShort(), stream.ReadShort(), stream.ReadShort(), stream.ReadShort());
ColorTable = _header.GlobalColorTable;
int flags = stream.Read();
if (UseLocalColorTable(flags))
{
ColorTable = await GIFColorTable.CreateColorTableAsync(stream, LocalColorTableSize(flags)).ConfigureAwait(false);
}
BackgroundColor = _header.BackgroundColor;
IsInterlaced = UseInterlace(flags);
}
void ParseGraphicControlExtension(GIFDecoderStreamReader stream)
{
int blockSize = stream.Read();
if (blockSize != 4)
{
throw new GIFDecoderFormatException("Invalid graphic control extension size.");
}
int flags = stream.Read();
SetDisposeMethod(flags);
SetDelay(stream.ReadShort());
SetTransparency(flags, stream.Read());
// Consume block terminator.
stream.Read();
}
async Task ParseApplicationExtensionAsync(GIFDecoderStreamReader stream)
{
var blockSize = await stream.ReadBlockAsync().ConfigureAwait(false);
if (blockSize >= NetscapeApplicationExtensionID.Length)
{
var buffer = stream.CurrentBlockBuffer;
string identifier = System.Text.Encoding.UTF8.GetString(buffer, 0, NetscapeApplicationExtensionID.Length);
if (identifier.Equals(NetscapeApplicationExtensionID, StringComparison.OrdinalIgnoreCase))
{
await ParseNetscapeApplicationExtensionAsync(stream).ConfigureAwait(false);
return;
}
}
await stream.SkipBlockAsync().ConfigureAwait(false);
return;
}
async Task ParseExtensionAsync(GIFDecoderStreamReader stream)
{
int blockCode = stream.Read();
switch (blockCode)
{
case GIFBlockCodes.GraphicsControlExtension:
ParseGraphicControlExtension(stream);
break;
case GIFBlockCodes.ApplicationExtensionBlock:
await ParseApplicationExtensionAsync(stream).ConfigureAwait(false);
break;
default:
await stream.SkipBlockAsync().ConfigureAwait(false);
break;
}
}
async Task ParseNetscapeApplicationExtensionAsync(GIFDecoderStreamReader stream)
{
int blockSize = await stream.ReadBlockAsync().ConfigureAwait(false);
while (blockSize > 0)
{
if (stream.CurrentBlockBuffer[0] == 1 && blockSize == 3)
{
int count = (stream.CurrentBlockBuffer[2] << 8) | stream.CurrentBlockBuffer[1];
if (count == 0)
{
LoopCount = int.MaxValue;
}
else if (count != 0)
{
LoopCount = count;
}
}
blockSize = await stream.ReadBlockAsync().ConfigureAwait(false);
}
}
async Task ParseAsync(GIFDecoderStreamReader stream)
{
int toRead = _colorData.Length;
int bytesRead = await stream.ReadAsync(_colorData, toRead).ConfigureAwait(false);
if (bytesRead < toRead)
{
throw new GIFDecoderFormatException("Invalid color table size.");
}
int currentColor = 0;
int currentColorData = 0;
while (currentColor < _size)
{
int r = _colorData[currentColorData++];
int g = _colorData[currentColorData++];
int b = _colorData[currentColorData++];
var rgb = (r << 16) | (g << 8) | b;
_colorTable[currentColor++] = (int)(0xFF000000 | rgb);
}
}
public async Task DecodeAsync(GIFDecoderStreamReader stream, int width, int height)
{
int pixelCount = width * height;
InitializeBuffers(pixelCount);
int nullCode = -1;
int inCode = nullCode;
int oldCode = nullCode;
int currentCode = nullCode;
int dataSize = stream.Read();
int codeSize = dataSize + 1;
int codeMask = (1 << codeSize) - 1;
int clearCode = 1 << dataSize;
int endOfInformationCode = clearCode + 1;
int availableCode = clearCode + 2;
for (currentCode = 0; currentCode < clearCode; currentCode++)
{
_prefix[currentCode] = 0;
_suffix[currentCode] = (byte)currentCode;
}
int datum = 0;
int bits = 0;
int count = 0;
int firstCode = 0;
int currentStackIndex = 0;
int currentPixelIndex = 0;
int currentBitIndex = 0;
int i = 0;
for (i = 0; i < pixelCount;)
{
if (currentStackIndex == 0)
{
if (bits < codeSize)
{
if (count == 0)
{
count = await stream.ReadBlockAsync().ConfigureAwait(false);
if (count <= 0)
{
break;
}
currentBitIndex = 0;
}
datum += (stream.CurrentBlockBuffer[currentBitIndex] << bits);
bits += 8;
currentBitIndex++;
count--;
continue;
}
currentCode = datum & codeMask;
datum >>= codeSize;
bits -= codeSize;
if ((currentCode > availableCode) || (currentCode == endOfInformationCode))
{
break;
}
if (currentCode == clearCode)
{
codeSize = dataSize + 1;
codeMask = (1 << codeSize) - 1;
availableCode = clearCode + 2;
oldCode = nullCode;
continue;
}
if (oldCode == nullCode)
{
_pixelStack[currentStackIndex++] = _suffix[currentCode];
oldCode = currentCode;
firstCode = currentCode;
continue;
}
inCode = currentCode;
if (currentCode == availableCode)
{
_pixelStack[currentStackIndex++] = (byte)firstCode;
currentCode = oldCode;
}
while (currentCode > clearCode)
{
_pixelStack[currentStackIndex++] = _suffix[currentCode];
currentCode = _prefix[currentCode];
}
firstCode = _suffix[currentCode];
if (availableCode >= DecoderStackSize)
{
break;
}
_pixelStack[currentStackIndex++] = (byte)firstCode;
_prefix[availableCode] = (short)oldCode;
_suffix[availableCode] = (byte)firstCode;
availableCode++;
if (((availableCode & codeMask) == 0) && (availableCode < DecoderStackSize))
{
codeSize++;
codeMask += availableCode;
}
oldCode = inCode;
}
currentStackIndex--;
_pixels[currentPixelIndex++] = _pixelStack[currentStackIndex];
i++;
}
for (i = currentPixelIndex; i < pixelCount; i++)
{
_pixels[i] = 0;
}
}
