Fix GIF decoder not handling deferred clear codes properly

Author: UnknownShadow200

MCGalaxy/util/Imaging/GifDecoder.cs

@@ -103,7 +103,7 @@ void ReadMarkers(byte[] src, SimpleBitmap bmp) {
                     case MARKER_IMAGE_END:
                         return;
                     default:
-                        Fail("unknown marker");
+                        Fail("unknown marker:" + marker.ToString("X2"));
                         break;
                 }
             }
@@ -251,9 +251,7 @@ void ReadImage(byte[] src, SimpleBitmap bmp) {
                     break;
                 }
 
-                if (code > availCode) {
-                    Fail("invalid code");
-                }
+                if (code > availCode) Fail("invalid code");
 
                 // Add new entry to code table unless it's full
                 // GIF spec allows this as per 'deferred clear codes'
@@ -268,15 +266,14 @@ void ReadImage(byte[] src, SimpleBitmap bmp) {
 
                     // Check if inserted code was last free entry of table
                     // If this is the case, then the table is immediately expanded
-                    if ((availCode & codeMask) == 0 && availCode != (MAX_CODES - 1)) {
+                    if ((availCode & codeMask) == 0 && availCode != MAX_CODES) {
                         codeLen++;
                         codeMask = (1 << codeLen) - 1;
                         Array.Resize(ref dict, 1 << codeLen);
                     }
                 }
 
                 prevCode = code;
-                // TODO output code
 
                 // "top" entry is actually last entry in chain
                 int chain_len = dict[code].len;

MCGalaxy/util/Imaging/JpegDecoder.cs

@@ -31,8 +31,50 @@ public static bool DetectHeader(byte[] data) {
         }
 
         public override SimpleBitmap Decode(byte[] src) {
+            SetBuffer(src);
+            SimpleBitmap bmp = new SimpleBitmap();
+            
+            ReadMarkers(src, bmp);
             Fail("JPEG decoder unfinished");
             return null;
         }
+        
+        const ushort MARKER_IMAGE_BEG = 0xFFD8;
+        const ushort MARKER_IMAGE_END = 0xFFD9;
+        const ushort MARKER_APP0      = 0xFFE0;
+        const ushort MARKER_TBL_QUANT = 0xFFDB;
+        const ushort MARKER_TBL_HUFF  = 0xFFC4;
+        
+        void ReadMarkers(byte[] src, SimpleBitmap bmp) {
+            for (;;)
+            {
+                int offset    = AdvanceOffset(2);
+                ushort marker = MemUtils.ReadU16_BE(src, offset);
+                
+                switch (marker)
+                {
+                    case MARKER_IMAGE_BEG:
+                        break; // Nothing to do
+                    case MARKER_IMAGE_END:
+                        return;
+                    case MARKER_APP0:
+                    case MARKER_TBL_QUANT:
+                    case MARKER_TBL_HUFF:
+                        SkipMarker(src);
+                        break;
+                        
+                    default:
+                        Fail("unknown marker:" + marker.ToString("X4"));
+                        break;
+                }
+            }
+        }
+        
+        void SkipMarker(byte[] src) {
+            int offset = AdvanceOffset(2);
+            ushort len = MemUtils.ReadU16_BE(src, offset);
+            // length *includes* 2 bytes of length
+            AdvanceOffset(len - 2);
+        }
     }
 }