Fix issue by cloning template objects and overriding GID's in tmj parsing

src/DotTiled/Layers/Objects/EllipseObject.cs

@@ -1,7 +1,25 @@
+using System.Linq;
+
 namespace DotTiled;
 
 /// <summary>
 /// An ellipse object in a map. The existing <see cref="Object.X"/>, <see cref="Object.Y"/>, <see cref="Object.Width"/>,
 /// and <see cref="Object.Height"/> properties are used to determine the size of the ellipse.
 /// </summary>
-public class EllipseObject : Object { }
+public class EllipseObject : Object
+{
+  internal override Object Clone() => new EllipseObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+  };
+}

src/DotTiled/Layers/Objects/Object.cs

@@ -64,4 +64,10 @@ public abstract class Object : HasPropertiesBase
 
   /// <inheritdoc/>
   public override IList<IProperty> GetProperties() => Properties;
+
+  /// <summary>
+  /// Creates a deep copy of the object.
+  /// </summary>
+  /// <returns></returns>
+  internal abstract Object Clone();
 }

src/DotTiled/Layers/Objects/PointObject.cs

@@ -1,7 +1,25 @@
+using System.Linq;
+
 namespace DotTiled;
 
 /// <summary>
 /// A point object in a map. The existing <see cref="Object.X"/> and <see cref="Object.Y"/> properties are used to
 /// determine the position of the point.
 /// </summary>
-public class PointObject : Object { }
+public class PointObject : Object
+{
+  internal override Object Clone() => new PointObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+  };
+}

src/DotTiled/Layers/Objects/PolygonObject.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using System.Numerics;
 
 namespace DotTiled;
@@ -14,4 +15,20 @@ public class PolygonObject : Object
   /// <see cref="Object.X"/> and <see cref="Object.Y"/> are used as the origin of the polygon.
   /// </summary>
   public required List<Vector2> Points { get; set; }
+
+  internal override Object Clone() => new PolygonObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+    Points = Points.ToList(),
+  };
 }

src/DotTiled/Layers/Objects/PolylineObject.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using System.Numerics;
 
 namespace DotTiled;
@@ -13,4 +14,20 @@ public class PolylineObject : Object
   /// The points that make up the polyline. <see cref="Object.X"/> and <see cref="Object.Y"/> are used as the origin of the polyline.
   /// </summary>
   public required List<Vector2> Points { get; set; }
+
+  internal override Object Clone() => new PolylineObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+    Points = Points.ToList(),
+  };
 }

src/DotTiled/Layers/Objects/RectangleObject.cs

@@ -1,7 +1,25 @@
+using System.Linq;
+
 namespace DotTiled;
 
 /// <summary>
 /// A rectangle object in a map. The existing <see cref="Object.X"/>, <see cref="Object.Y"/>, <see cref="Object.Width"/>,
 /// and <see cref="Object.Height"/> properties are used to determine the size of the rectangle.
 /// </summary>
-public class RectangleObject : Object { }
+public class RectangleObject : Object
+{
+  internal override Object Clone() => new RectangleObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+  };
+}

src/DotTiled/Layers/Objects/TextObject.cs

@@ -1,4 +1,5 @@
 using System.Globalization;
+using System.Linq;
 
 namespace DotTiled;
 
@@ -113,4 +114,32 @@ public class TextObject : Object
   /// The text to be displayed.
   /// </summary>
   public string Text { get; set; } = "";
+
+  internal override Object Clone() => new TextObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+
+    FontFamily = FontFamily,
+    PixelSize = PixelSize,
+    Wrap = Wrap,
+    Color = Color,
+    Bold = Bold,
+    Italic = Italic,
+    Underline = Underline,
+    Strikeout = Strikeout,
+    Kerning = Kerning,
+    HorizontalAlignment = HorizontalAlignment,
+    VerticalAlignment = VerticalAlignment,
+    Text = Text,
+  };
 }

src/DotTiled/Layers/Objects/TileObject.cs

@@ -1,3 +1,5 @@
+using System.Linq;
+
 namespace DotTiled;
 
 /// <summary>
@@ -14,4 +16,21 @@ public class TileObject : Object
   /// The flipping flags for the tile.
   /// </summary>
   public FlippingFlags FlippingFlags { get; set; }
+
+  internal override Object Clone() => new TileObject
+  {
+    ID = ID,
+    Name = Name,
+    Type = Type,
+    X = X,
+    Y = Y,
+    Width = Width,
+    Height = Height,
+    Rotation = Rotation,
+    Visible = Visible,
+    Template = Template,
+    Properties = Properties.Select(p => p.Clone()).ToList(),
+    GID = GID,
+    FlippingFlags = FlippingFlags,
+  };
 }

src/DotTiled/Serialization/Tmj/TmjReaderBase.Data.cs

@@ -19,8 +19,7 @@ public abstract partial class TmjReaderBase
 
   internal static Chunk ReadChunk(JsonElement element, Optional<DataCompression> compression, DataEncoding encoding)
   {
-    var data = ReadDataWithoutChunks(element, compression, encoding);
-
+    var data = element.GetRequiredPropertyCustom<Data>("data", e => ReadDataWithoutChunks(e, compression, encoding));
     var x = element.GetRequiredProperty<int>("x");
     var y = element.GetRequiredProperty<int>("y");
     var width = element.GetRequiredProperty<int>("width");

src/DotTiled/Serialization/Tmj/TmjReaderBase.ObjectLayer.cs

@@ -76,12 +76,13 @@ public abstract partial class TmjReaderBase
     List<Vector2> polygonDefault = null;
     List<Vector2> polylineDefault = null;
     List<IProperty> propertiesDefault = [];
+    Optional<uint> gidDefault = Optional.Empty;
 
     var template = element.GetOptionalProperty<string>("template");
     if (template.HasValue)
     {
       var resolvedTemplate = _externalTemplateResolver(template.Value);
-      var templObj = resolvedTemplate.Object;
+      var templObj = resolvedTemplate.Object.Clone();
 
       idDefault = templObj.ID;
       nameDefault = templObj.Name;
@@ -97,10 +98,11 @@ public abstract partial class TmjReaderBase
       pointDefault = templObj is PointObject;
       polygonDefault = (templObj is PolygonObject polygonObj) ? polygonObj.Points : null;
       polylineDefault = (templObj is PolylineObject polylineObj) ? polylineObj.Points : null;
+      gidDefault = (templObj is TileObject tileObj) ? tileObj.GID : Optional.Empty;
     }
 
     var ellipse = element.GetOptionalProperty<bool>("ellipse").GetValueOr(ellipseDefault);
-    var gid = element.GetOptionalProperty<uint>("gid");
+    var gid = element.GetOptionalProperty<uint>("gid").GetValueOrOptional(gidDefault);
     var height = element.GetOptionalProperty<float>("height").GetValueOr(heightDefault);
     var id = element.GetOptionalProperty<uint>("id").GetValueOrOptional(idDefault);
     var name = element.GetOptionalProperty<string>("name").GetValueOr(nameDefault);

src/DotTiled/Serialization/Tmx/TmxReaderBase.ObjectLayer.cs

@@ -74,7 +74,7 @@ public abstract partial class TmxReaderBase
     var template = _reader.GetOptionalAttribute("template");
     DotTiled.Object obj = null;
     if (template.HasValue)
-      obj = _externalTemplateResolver(template.Value).Object;
+      obj = _externalTemplateResolver(template.Value).Object.Clone();
 
     uint idDefault = obj?.ID.GetValueOr(0) ?? 0;
     string nameDefault = obj?.Name ?? "";