项目结构调整

Others/WpfAnimatedGif/Decoding/GifImageDescriptor.cs

@@ -0,0 +1,43 @@
+using System;
+using System.IO;
+
+namespace WpfAnimatedGif.Decoding
+{
+    internal class GifImageDescriptor
+    {
+        public int Left { get; private set; }
+        public int Top { get; private set; }
+        public int Width { get; private set; }
+        public int Height { get; private set; }
+        public bool HasLocalColorTable { get; private set; }
+        public bool Interlace { get; private set; }
+        public bool IsLocalColorTableSorted { get; private set; }
+        public int LocalColorTableSize { get; private set; }
+
+        private GifImageDescriptor()
+        {
+        }
+
+        internal static GifImageDescriptor ReadImageDescriptor(Stream stream)
+        {
+            var descriptor = new GifImageDescriptor();
+            descriptor.Read(stream);
+            return descriptor;
+        }
+
+        private void Read(Stream stream)
+        {
+            byte[] bytes = new byte[9];
+            stream.ReadAll(bytes, 0, bytes.Length);
+            Left = BitConverter.ToUInt16(bytes, 0);
+            Top = BitConverter.ToUInt16(bytes, 2);
+            Width = BitConverter.ToUInt16(bytes, 4);
+            Height = BitConverter.ToUInt16(bytes, 6);
+            byte packedFields = bytes[8];
+            HasLocalColorTable = (packedFields & 0x80) != 0;
+            Interlace = (packedFields & 0x40) != 0;
+            IsLocalColorTableSorted = (packedFields & 0x20) != 0;
+            LocalColorTableSize = 1 << ((packedFields & 0x07) + 1);
+        }
+    }
+}