/// <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);
}
}