private void ReadFrameColors(byte[] indices, byte[] colorTable, GifImageDescriptor descriptor)
{
int imageWidth = _descriptor.Width;
int imageHeight = _descriptor.Height;
if (_currentFrame == null)
{
_currentFrame = new byte[imageWidth * imageHeight * 4];
}
byte[] lastFrame = null;
if (_graphicsControl != null &&
_graphicsControl.DisposalMethod == DisposalMethod.RestoreToPrevious)
{
lastFrame = new byte[imageWidth * imageHeight * 4];
Array.Copy(_currentFrame, lastFrame, lastFrame.Length);
}
int offset = 0, i = 0, index = -1;
int iPass = 0; // the interlace pass
int iInc = 8; // the interlacing line increment
int iY = 0; // the current interlaced line
int writeY = 0; // the target y offset to write to
for (int y = descriptor.Top; y < descriptor.Top + descriptor.Height; y++)
{
// Check if this image is interlaced.
if (descriptor.InterlaceFlag)
{
// If so then we read lines at predetermined offsets.
// When an entire image height worth of offset lines has been read we consider this a pass.
// With each pass the number of offset lines changes and the starting line changes.
if (iY >= descriptor.Height)
{
iPass++;
switch (iPass)
{
case 1:
iY = 4;
break;
case 2:
iY = 2;
iInc = 4;
break;
case 3:
iY = 1;
iInc = 2;
break;
}
}
writeY = iY + descriptor.Top;
iY += iInc;
}
else
{
writeY = y;
}
for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width; x++)
{
offset = writeY * imageWidth + x;
index = indices[i];
if (_graphicsControl == null ||
_graphicsControl.TransparencyFlag == false ||
_graphicsControl.TransparencyIndex != index)
{
_currentFrame[offset * 4 + 0] = colorTable[index * 3 + 2];
_currentFrame[offset * 4 + 1] = colorTable[index * 3 + 1];
_currentFrame[offset * 4 + 2] = colorTable[index * 3 + 0];
_currentFrame[offset * 4 + 3] = (byte)255;
}
i++;
}
}
var pixels = new byte[imageWidth * imageHeight * 4];
Array.Copy(_currentFrame, pixels, pixels.Length);
_frames.Add(new Image(imageWidth, imageHeight, pixels));
if (_graphicsControl != null)
{
if (_graphicsControl.DisposalMethod == DisposalMethod.RestoreToBackground)
{
for (int y = descriptor.Top; y < descriptor.Top + descriptor.Height; y++)
{
for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width; x++)
{
offset = y * imageWidth + x;
_currentFrame[offset * 4 + 0] = 0;
_currentFrame[offset * 4 + 1] = 0;
_currentFrame[offset * 4 + 2] = 0;
_currentFrame[offset * 4 + 3] = 0;
}
}
}
else if (_graphicsControl.DisposalMethod == DisposalMethod.RestoreToPrevious)
{
_currentFrame = lastFrame;
}
}
}
private byte[] ReadFrameIndices(GifImageDescriptor imageDescriptor)
{
int dataSize = _stream.ReadByte();
LZWDecoder lzwDecoder = new LZWDecoder(_stream);
byte[] indices = lzwDecoder.DecodePixels(imageDescriptor.Width, imageDescriptor.Height, dataSize);
return indices;
}
private byte[] ReadFrameLocalColorTable(GifImageDescriptor imageDescriptor)
{
byte[] localColorTable = null;
if (imageDescriptor.LocalColorTableFlag == true)
{
localColorTable = new byte[imageDescriptor.LocalColorTableSize * 3];
_stream.Read(localColorTable, 0, localColorTable.Length);
}
return localColorTable;
}
private GifImageDescriptor ReadImageDescriptor()
{
byte[] buffer = new byte[9];
_stream.Read(buffer, 0, buffer.Length);
byte packed = buffer[8];
GifImageDescriptor imageDescriptor = new GifImageDescriptor();
imageDescriptor.Left = BitConverter.ToInt16(buffer, 0);
imageDescriptor.Top = BitConverter.ToInt16(buffer, 2);
imageDescriptor.Width = BitConverter.ToInt16(buffer, 4);
imageDescriptor.Height = BitConverter.ToInt16(buffer, 6);
imageDescriptor.LocalColorTableFlag = ((packed & 0x80) >> 7) == 1;
imageDescriptor.LocalColorTableSize = 2 << (packed & 0x07);
imageDescriptor.InterlaceFlag = ((packed & 0x40) >> 6) == 1;
return imageDescriptor;
}