Fix UOP frame header bounds and center off-by-one

Ultima/AnimationsUopLoader.cs

@@ -22,6 +22,9 @@ internal static class AnimationsUopLoader
         internal const int _maxAnimActions = 80;
         private const int _maxDirections = 5;
 
+        /// <summary>"AMOU", the first four bytes of every animation frame payload.</summary>
+        private const uint _frameMagic = 0x554F4D41;
+
         /// <summary>
         /// Size of the fixed part of one AnimationSequence group record: the four leading fields,
         /// the per frame bytes and the reserved block. Two variable length lists follow it.
@@ -568,14 +571,20 @@ private static byte[] ReadEntryData(UopEntry entry)
 
         private static AnimationFrame[] ParseUopFrames(byte[] data, int direction, bool flip)
         {
-            if (data.Length < 36)
+            // The header is 40 bytes; frame count and table offset sit at 32 and 36
+            if (data.Length < 40)
             {
                 return null;
             }
 
             using var memoryStream = new MemoryStream(data);
             using var reader = new BinaryReader(memoryStream);
 
+            if (reader.ReadUInt32() != _frameMagic)
+            {
+                return null;
+            }
+
             reader.BaseStream.Seek(32, SeekOrigin.Begin);
             int frameCount = reader.ReadInt32();
             uint dataStart = reader.ReadUInt32();

UoFiddler.Controls/Forms/AnimationEditForm.cs

@@ -1043,7 +1043,7 @@ private void OnFrameCountBarChanged(object sender, EventArgs e)
             }
 
             AnimIdx edit = AnimationEdit.GetAnimation(_fileType, _currentBody, _currentAction, _currentDir);
-            if (edit != null && edit.Frames.Count >= FramesTrackBar.Value)
+            if (edit != null && edit.Frames.Count > FramesTrackBar.Value)
             {
                 CenterXNumericUpDown.Value = edit.Frames[FramesTrackBar.Value].Center.X;
                 CenterYNumericUpDown.Value = edit.Frames[FramesTrackBar.Value].Center.Y;