private static void ReadImage(StreamHelper streamHelper, Stream fs, GifImage gifImage, List <GraphicEx> graphics, int frameCount)
{
ImageDescriptor imgDes = streamHelper.GetImageDescriptor(fs);
GifFrame frame = new GifFrame();
frame.ImageDescriptor = imgDes;
frame.LocalColorTable = gifImage.GlobalColorTable;
if (imgDes.LctFlag)
{
frame.LocalColorTable = streamHelper.ReadByte(imgDes.LctSize * 3);
}
LZWDecoder lzwDecoder = new LZWDecoder(fs);
int dataSize = streamHelper.Read();
frame.ColorDepth = dataSize;
byte[] pixels = lzwDecoder.DecodeImageData(imgDes.Width, imgDes.Height, dataSize, imgDes.InterlaceFlag);
frame.IndexedPixel = pixels;
int blockSize = streamHelper.Read();
DataStruct data = new DataStruct(blockSize, fs);
GraphicEx graphicEx = null;
if (graphics.Count > 0)
{
graphicEx = graphics[frameCount];
}
frame.GraphicExtension = graphicEx;
// Handle delta GIF images
WriteableBitmap prev;
if ((gifImage.LogicalScreenDescriptor.Packed == 245) && (frameCount > 0))
{
prev = gifImage.Frames[frameCount - 1].Image;
}
else
{
prev = null;
}
WriteableBitmap img = GetImageFromPixel(pixels, frame.Palette, imgDes.InterlaceFlag, imgDes.Width, imgDes.Height, prev);
frame.Image = img;
gifImage.Frames.Add(frame);
}
/// <summary>
/// 从文件数据流中读取图形控制扩展(Graphic Control Extension)
/// </summary>
/// <param name="stream"></param>
/// <returns></returns>
public GraphicEx GetGraphicControlExtension(Stream stream)
{
GraphicEx gex = new GraphicEx();
int blockSize = Read();
if (blockSize != GraphicEx.BlockSize)
{
throw new Exception("数据格式错误！");
}
gex.Packed = (byte)Read();
gex.TransparencyFlag = (gex.Packed & 0x01) == 1;
gex.DisposalMethod = (gex.Packed & 0x1C) >> 2;
gex.Delay = ReadShort();
gex.TranIndex = (byte)Read();
Read();
return(gex);
}
public static GifImage Decode(Stream fs)
{
StreamHelper streamHelper = null;
GifImage gifImage = new GifImage();
List <GraphicEx> graphics = new List <GraphicEx>();
int frameCount = 0;
streamHelper = new StreamHelper(fs);
gifImage.Header = streamHelper.ReadString(6);
gifImage.LogicalScreenDescriptor = streamHelper.GetLCD(fs);
if (gifImage.LogicalScreenDescriptor.GlobalColorTableFlag)
{
gifImage.GlobalColorTable = streamHelper.ReadByte(gifImage.LogicalScreenDescriptor.GlobalColorTableSize * 3);
}
int nextFlag = streamHelper.Read();
while (nextFlag != 0)
{
if (nextFlag == GifExtensions.ImageLabel)
{
ReadImage(streamHelper, fs, gifImage, graphics, frameCount);
frameCount++;
}
else if (nextFlag == GifExtensions.ExtensionIntroducer)
{
int gcl = streamHelper.Read();
switch (gcl)
{
case GifExtensions.GraphicControlLabel:
{
GraphicEx graphicEx = streamHelper.GetGraphicControlExtension(fs);
graphics.Add(graphicEx);
break;
}
case GifExtensions.CommentLabel:
{
CommentEx comment = streamHelper.GetCommentEx(fs);
gifImage.CommentExtensions.Add(comment);
break;
}
case GifExtensions.ApplicationExtensionLabel:
{
ApplicationEx applicationEx = streamHelper.GetApplicationEx(fs);
gifImage.ApplictionExtensions.Add(applicationEx);
break;
}
case GifExtensions.PlainTextLabel:
{
PlainTextEx textEx = streamHelper.GetPlainTextEx(fs);
gifImage.PlainTextEntensions.Add(textEx);
break;
}
}
}
else if (nextFlag == GifExtensions.EndIntroducer)
{
break;
}
nextFlag = streamHelper.Read();
}
return(gifImage);
}
