项目结构调整

Others/WpfAnimatedGif/Decoding/GifExtension.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.IO;
+
+namespace WpfAnimatedGif.Decoding
+{
+    internal abstract class GifExtension : GifBlock
+    {
+        internal const int ExtensionIntroducer = 0x21;
+
+        internal static GifExtension ReadExtension(Stream stream, IEnumerable<GifExtension> controlExtensions, bool metadataOnly)
+        {
+            // Note: at this point, the Extension Introducer (0x21) has already been read
+
+            int label = stream.ReadByte();
+            if (label < 0)
+                throw GifHelpers.UnexpectedEndOfStreamException();
+            switch (label)
+            {
+                case GifGraphicControlExtension.ExtensionLabel:
+                    return GifGraphicControlExtension.ReadGraphicsControl(stream);
+                case GifCommentExtension.ExtensionLabel:
+                    return GifCommentExtension.ReadComment(stream);
+                case GifPlainTextExtension.ExtensionLabel:
+                    return GifPlainTextExtension.ReadPlainText(stream, controlExtensions, metadataOnly);
+                case GifApplicationExtension.ExtensionLabel:
+                    return GifApplicationExtension.ReadApplication(stream);
+                default:
+                    throw GifHelpers.UnknownExtensionTypeException(label);
+            }
+        }
+    }
+}