private static void ReadImage(GifStream stream, GifImage gifImage, List <GraphicEx> graphics,
int frameCount)
{
var imageDescriptor = stream.GetImageDescriptor();
var frame = new GifFrame {
ImageDescriptor = imageDescriptor, LocalColorTable = gifImage.GlobalColorTable
};
if (imageDescriptor.LocalColorTableFlag)
{
frame.LocalColorTable = stream.ReadByte(imageDescriptor.LocalColorTableSize * 3);
}
var lzwDecoder = new LZWDecoder(stream);
var dataSize = stream.Read();
frame.ColorDepth = dataSize;
var pixel = lzwDecoder.DecodeImageData(imageDescriptor.Width, imageDescriptor.Height, dataSize);
frame.IndexedPixel = pixel;
var blockSize = stream.Read();
_ = new DataStruct(blockSize, stream);
var graphicEx = graphics[frameCount];
frame.GraphicExtension = graphicEx;
frame.Image = GetImageFromPixel(pixel, imageDescriptor.Width, imageDescriptor.Height, frame.Palette,
imageDescriptor.InterlaceFlag);
gifImage.Frames.Add(frame);
}
internal DataStruct(int blockSize, GifStream streamHelper)
{
BlockSize = (byte)blockSize;
if (BlockSize > 0)
{
Data = streamHelper.ReadByte(BlockSize);
}
}
internal DataStruct(int blockSize, Stream stream)
{
var streamHelper = new GifStream(stream);
BlockSize = (byte)blockSize;
if (BlockSize > 0)
{
Data = streamHelper.ReadByte(BlockSize);
}
}
/// <summary>
/// 对gif图像文件进行解码
/// </summary>
/// <param name="gifPath">gif文件路径</param>
internal static GifImage Decode(string gifPath)
{
using (var stream = new GifStream(new FileStream(gifPath, FileMode.Open)))
{
var gifImage = new GifImage();
var graphics = new List <GraphicEx>();
var frameCount = 0;
//读取文件头
//开始6字节是GIF署名 文件版本号，GIF署名 是“GIF”，文件版本号为 "87a"或"89a"
//87a 是 1987 版，89a 是 1989 提出的，所以就需要跳过 6 字节
gifImage.Header = stream.ReadString(6);
//读取逻辑屏幕标示符
gifImage.LogicalScreenDescriptor = stream.GetLogicalScreenDescriptor();
if (gifImage.LogicalScreenDescriptor.GlobalColorTableFlag)
{
//读取全局颜色列表
gifImage.GlobalColorTable =
stream.ReadByte(gifImage.LogicalScreenDescriptor.GlobalColorTableSize * 3);
}
int nextFlag;
while ((nextFlag = stream.Read()) != GifExtensions.Terminator)
{
if (nextFlag == GifExtensions.ImageLabel)
{
ReadImage(stream, gifImage, graphics, frameCount);
frameCount++;
}
else if (nextFlag == GifExtensions.ExtensionIntroducer)
{
var gcl = stream.Read();
switch (gcl)
{
case GifExtensions.GraphicControlLabel:
{
var graphicEx = stream.GetGraphicControlExtension();
graphics.Add(graphicEx);
break;
}
case GifExtensions.CommentLabel:
{
var comment = stream.GetCommentEx();
gifImage.CommentExtensions.Add(comment);
break;
}
case GifExtensions.ApplicationExtensionLabel:
{
var applicationEx = stream.GetApplicationEx();
gifImage.ApplictionExtensions.Add(applicationEx);
break;
}
case GifExtensions.PlainTextLabel:
{
var textEx = stream.GetPlainTextEx();
gifImage.PlainTextExtensions.Add(textEx);
break;
}
}
}
else if (nextFlag == GifExtensions.EndIntroducer)
{
//到了文件尾
break;
}
}
return(gifImage);
}
}
