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);
}
private void ReadFrame()
{
GifImageDescriptor imageDescriptor = ReadImageDescriptor();
byte[] localColorTable = ReadFrameLocalColorTable(imageDescriptor);
byte[] indices = ReadFrameIndices(imageDescriptor);
// Determine the color table for this frame. If there is a local one, use it
// otherwise use the global color table.
byte[] colorTable = localColorTable != null ? localColorTable : _globalColorTable;
ReadFrameColors(indices, colorTable, imageDescriptor);
int blockSize = _stream.ReadByte();
if (blockSize > 0)
{
_stream.Seek(blockSize, SeekOrigin.Current);
}
}
private void ReadFrameColors(byte[] indices, byte[] colorTable, GifImageDescriptor descriptor)
{
int imageWidth = _logicalScreenDescriptor.Width;
int imageHeight = _logicalScreenDescriptor.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 + 0];
_currentFrame[offset * 4 + 1] = colorTable[index * 3 + 1];
_currentFrame[offset * 4 + 2] = colorTable[index * 3 + 2];
_currentFrame[offset * 4 + 3] = (byte)255;
}
i++;
}
}
byte[] pixels = new byte[imageWidth * imageHeight * 4];
Array.Copy(_currentFrame, pixels, pixels.Length);
_currentFrame = new byte[imageWidth * imageHeight * 4];
GifFrame frame = new GifFrame(imageWidth, imageHeight);
int indx = 0;
byte r, g, b, a;
for (uint y = 0; y < frame.height; y++)
{
for (uint x = 0; x < frame.width; x++)
{
r = pixels[indx];
indx++;
g = pixels[indx];
indx++;
b = pixels[indx];
indx++;
a = pixels[indx];
indx++;
frame.SetPixelEx(x, y, new Color32(r, g, b, a));
}
}
pixels = null;
System.GC.Collect();
_image.AddFrame(frame);
if (_graphicsControl != null)
{
if (_graphicsControl.DelayTime > 0)
{
_image.timePerFrame = _graphicsControl.DelayTime;
}
if (_graphicsControl.DisposalMethod == DisposalMethod.RestoreToBackground)
{
//GifFrame im = new GifFrame(imageWidth, imageHeight);
//im.Clear(new Color32(0,0,0,0));
//_image.AddFrame(im);
//_image.loop = false;
}
else if (_graphicsControl.DisposalMethod == DisposalMethod.RestoreToPrevious)
{
_image.loop = true;
}
}
}
