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 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;
}
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;
}
}
