/// <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>
internal 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);
}
/// <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)
{
FileStream fs = null;
StreamHelper streamHelper = null;
GifImage gifImage = new GifImage();
List <GraphicEx> graphics = new List <GraphicEx>();
int frameCount = 0;
try
{
fs = new FileStream(gifPath, FileMode.Open);
streamHelper = new StreamHelper(fs);
//读取文件头
gifImage.Header = streamHelper.ReadString(6);
//读取逻辑屏幕标示符
gifImage.LogicalScreenDescriptor = streamHelper.GetLCD(fs);
if (gifImage.LogicalScreenDescriptor.GlobalColorTableFlag)
{
//读取全局颜色列表
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)
{
//到了文件尾
break;
}
nextFlag = streamHelper.Read();
}
}
catch
{
throw;
}
finally
{
fs.Close();
}
return(gifImage);
}