项目结构调整

Others/WpfAnimatedGif/Decoding/GifLogicalScreenDescriptor.cs

@@ -0,0 +1,43 @@
+using System;
+using System.IO;
+
+namespace WpfAnimatedGif.Decoding
+{
+    internal class GifLogicalScreenDescriptor
+    {
+        public int Width { get; private set; }
+        public int Height { get; private set; }
+        public bool HasGlobalColorTable { get; private set; }
+        public int ColorResolution { get; private set; }
+        public bool IsGlobalColorTableSorted { get; private set; }
+        public int GlobalColorTableSize { get; private set; }
+        public int BackgroundColorIndex { get; private set; }
+        public double PixelAspectRatio { get; private set; }
+
+        internal static GifLogicalScreenDescriptor ReadLogicalScreenDescriptor(Stream stream)
+        {
+            var descriptor = new GifLogicalScreenDescriptor();
+            descriptor.Read(stream);
+            return descriptor;
+        }
+
+        private void Read(Stream stream)
+        {
+            byte[] bytes = new byte[7];
+            stream.ReadAll(bytes, 0, bytes.Length);
+
+            Width = BitConverter.ToUInt16(bytes, 0);
+            Height = BitConverter.ToUInt16(bytes, 2);
+            byte packedFields = bytes[4];
+            HasGlobalColorTable = (packedFields & 0x80) != 0;
+            ColorResolution = ((packedFields & 0x70) >> 4) + 1;
+            IsGlobalColorTableSorted = (packedFields & 0x08) != 0;
+            GlobalColorTableSize = 1 << ((packedFields & 0x07) + 1);
+            BackgroundColorIndex = bytes[5];
+            PixelAspectRatio =
+                bytes[5] == 0
+                    ? 0.0
+                    : (15 + bytes[5]) / 64.0;
+        }
+    }
+}