项目结构调整

Others/WpfAnimatedGif/Decoding/GifHelpers.cs

@@ -0,0 +1,110 @@
+using System;
+using System.IO;
+using System.Text;
+
+namespace WpfAnimatedGif.Decoding
+{
+    internal static class GifHelpers
+    {
+        public static string ReadString(Stream stream, int length)
+        {
+            byte[] bytes = new byte[length];
+            stream.ReadAll(bytes, 0, length);
+            return Encoding.ASCII.GetString(bytes);
+        }
+
+        public static byte[] ReadDataBlocks(Stream stream, bool discard)
+        {
+            MemoryStream ms = discard ? null : new MemoryStream();
+            using (ms)
+            {
+                int len;
+                while ((len = stream.ReadByte()) > 0)
+                {
+                    byte[] bytes = new byte[len];
+                    stream.ReadAll(bytes, 0, len);
+                    if (ms != null)
+                        ms.Write(bytes, 0, len);
+                }
+                if (ms != null)
+                    return ms.ToArray();
+                return null;
+            }
+        }
+
+        public static GifColor[] ReadColorTable(Stream stream, int size)
+        {
+            int length = 3 * size;
+            byte[] bytes = new byte[length];
+            stream.ReadAll(bytes, 0, length);
+            GifColor[] colorTable = new GifColor[size];
+            for (int i = 0; i < size; i++)
+            {
+                byte r = bytes[3 * i];
+                byte g = bytes[3 * i + 1];
+                byte b = bytes[3 * i + 2];
+                colorTable[i] = new GifColor(r, g, b);
+            }
+            return colorTable;
+        }
+
+        public static bool IsNetscapeExtension(GifApplicationExtension ext)
+        {
+            return ext.ApplicationIdentifier == "NETSCAPE"
+                && Encoding.ASCII.GetString(ext.AuthenticationCode) == "2.0";
+        }
+
+        public static ushort GetRepeatCount(GifApplicationExtension ext)
+        {
+            if (ext.Data.Length >= 3)
+            {
+                return BitConverter.ToUInt16(ext.Data, 1);
+            }
+            return 1;
+        }
+
+        public static Exception UnexpectedEndOfStreamException()
+        {
+            return new GifDecoderException("Unexpected end of stream before trailer was encountered");
+        }
+
+        public static Exception UnknownBlockTypeException(int blockId)
+        {
+            return new GifDecoderException("Unknown block type: 0x" + blockId.ToString("x2"));
+        }
+
+        public static Exception UnknownExtensionTypeException(int extensionLabel)
+        {
+            return new GifDecoderException("Unknown extension type: 0x" + extensionLabel.ToString("x2"));
+        }
+
+        public static Exception InvalidBlockSizeException(string blockName, int expectedBlockSize, int actualBlockSize)
+        {
+            return new GifDecoderException(
+                string.Format(
+                    "Invalid block size for {0}. Expected {1}, but was {2}",
+                    blockName,
+                    expectedBlockSize,
+                    actualBlockSize));
+        }
+
+        public static Exception InvalidSignatureException(string signature)
+        {
+            return new GifDecoderException("Invalid file signature: " + signature);
+        }
+
+        public static Exception UnsupportedVersionException(string version)
+        {
+            return new GifDecoderException("Unsupported version: " + version);
+        }
+
+        public static void ReadAll(this Stream stream, byte[] buffer, int offset, int count)
+        {
+            int totalRead = 0;
+            while (totalRead < count)
+            {
+                totalRead += stream.Read(buffer, offset + totalRead, count - totalRead);
+            }
+        }
+    }
+}