private void ReadFrameColors(byte[] indices, byte[] colorTable, GifImageDescriptor descriptor)
{
int imageWidth = logicalScreenDescriptor.Width;
int imageHeight = logicalScreenDescriptor.Height;
if (currentFrame == null){
currentFrame = new Color2[imageWidth*imageHeight];
}
Color2[] lastFrame = null;
if (graphicsControlExtension != null && graphicsControlExtension.DisposalMethod == DisposalMethod.RestoreToPrevious){
lastFrame = new Color2[imageWidth*imageHeight];
Array.Copy(currentFrame, lastFrame, lastFrame.Length);
}
int offset, i = 0;
int interlacePass = 0; // The interlace pass
int interlaceIncrement = 8; // The interlacing line increment
int interlaceY = 0; // The current interlaced line
for (int y = descriptor.Top; y < descriptor.Top + descriptor.Height; y++){
// Check if this image is interlaced.
int writeY; // the target y offset to write to
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 (interlaceY >= descriptor.Height){
interlacePass++;
switch (interlacePass){
case 1:
interlaceY = 4;
break;
case 2:
interlaceY = 2;
interlaceIncrement = 4;
break;
case 3:
interlaceY = 1;
interlaceIncrement = 2;
break;
}
}
writeY = interlaceY + descriptor.Top;
interlaceY += interlaceIncrement;
} else{
writeY = y;
}
for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width; x++){
offset = (writeY*imageWidth) + x;
int index = indices[i];
if (graphicsControlExtension == null || graphicsControlExtension.TransparencyFlag == false ||
graphicsControlExtension.TransparencyIndex != index){
// Stored in r-> g-> b-> a order.
int indexOffset = index*3;
Color2 pixel = Color2.FromArgb(colorTable[indexOffset], colorTable[indexOffset + 1], colorTable[indexOffset + 2]);
currentFrame[offset] = pixel;
}
i++;
}
}
Color2[] pixels = new Color2[imageWidth*imageHeight];
Array.Copy(currentFrame, pixels, pixels.Length);
ImageBase currentImage;
if (decodedImage.Pixels == null){
currentImage = decodedImage;
currentImage.SetPixels(imageWidth, imageHeight, pixels);
currentImage.Quality = colorTable.Length/3;
if (graphicsControlExtension != null && graphicsControlExtension.DelayTime > 0){
decodedImage.FrameDelay = graphicsControlExtension.DelayTime;
}
} else{
ImageFrame frame = new ImageFrame();
currentImage = frame;
currentImage.SetPixels(imageWidth, imageHeight, pixels);
currentImage.Quality = colorTable.Length/3;
if (graphicsControlExtension != null && graphicsControlExtension.DelayTime > 0){
currentImage.FrameDelay = graphicsControlExtension.DelayTime;
}
decodedImage.Frames.Add(frame);
}
if (graphicsControlExtension != null){
if (graphicsControlExtension.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;
// Stored in r-> g-> b-> a order.
currentFrame[offset] = default(Color2);
}
}
} else if (graphicsControlExtension.DisposalMethod == DisposalMethod.RestoreToPrevious){
currentFrame = lastFrame;
}
}
}
private byte[] ReadFrameLocalColorTable(GifImageDescriptor imageDescriptor)
{
byte[] localColorTable = null;
if (imageDescriptor.LocalColorTableFlag){
localColorTable = new byte[imageDescriptor.LocalColorTableSize*3];
currentStream.Read(localColorTable, 0, localColorTable.Length);
}
return localColorTable;
}
private GifImageDescriptor ReadImageDescriptor()
{
byte[] buffer = new byte[9];
currentStream.Read(buffer, 0, buffer.Length);
byte packed = buffer[8];
GifImageDescriptor imageDescriptor = new GifImageDescriptor{
Left = BitConverter.ToInt16(buffer, 0),
Top = BitConverter.ToInt16(buffer, 2),
Width = BitConverter.ToInt16(buffer, 4),
Height = BitConverter.ToInt16(buffer, 6),
LocalColorTableFlag = ((packed & 0x80) >> 7) == 1,
LocalColorTableSize = 2 << (packed & 0x07),
InterlaceFlag = ((packed & 0x40) >> 6) == 1
};
return imageDescriptor;
}
private byte[] ReadFrameIndices(GifImageDescriptor imageDescriptor)
{
int dataSize = currentStream.ReadByte();
LzwDecoder lzwDecoder = new LzwDecoder(currentStream);
byte[] indices = lzwDecoder.DecodePixels(imageDescriptor.Width, imageDescriptor.Height, dataSize);
return indices;
}