From b7cc008326a9cabb55a1f29dd1e6078794798fac Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Tue, 14 Nov 2023 15:31:12 +0100
Subject: [PATCH 01/14] initial code for ext_instance_features

---
 build/SharpGLTF.CodeGen/Constants.cs          |   7 ++
 .../Ext.EXT_InstanceFeatures.cs               |  33 ++++++
 build/SharpGLTF.CodeGen/Program.cs            |   4 +-
 .../Schemas/EXT_instance_features/README.md   |   8 ++
 .../schema/featureId.schema.json              |  43 +++++++
 .../schema/featureIdAttribute.schema.json     |   8 ++
 .../node.EXT_instance_features.schema.json    |  27 +++++
 .../SharpGLTF.CodeGen.csproj                  |  12 ++
 .../Schema2/CesiumExtensions.cs               |   1 +
 .../Ext.CESIUM_ext_instance_features.g.cs     | 110 ++++++++++++++++++
 .../Schema2/MeshExtInstanceFeatures.cs        |  63 ++++++++++
 .../ExtInstanceFeaturesTests.cs               |  65 +++++++++++
 12 files changed, 380 insertions(+), 1 deletion(-)
 create mode 100644 build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs
 create mode 100644 build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/README.md
 create mode 100644 build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureId.schema.json
 create mode 100644 build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureIdAttribute.schema.json
 create mode 100644 build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/node.EXT_instance_features.schema.json
 create mode 100644 src/SharpGLTF.Cesium/Schema2/Generated/Ext.CESIUM_ext_instance_features.g.cs
 create mode 100644 src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
 create mode 100644 tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs

diff --git a/build/SharpGLTF.CodeGen/Constants.cs b/build/SharpGLTF.CodeGen/Constants.cs
index 335e7510..eecb3950 100644
--- a/build/SharpGLTF.CodeGen/Constants.cs
+++ b/build/SharpGLTF.CodeGen/Constants.cs
@@ -15,6 +15,8 @@ static class Constants
         /// </summary>
         public static string LocalRepoDirectory => System.IO.Path.Combine(System.IO.Path.GetDirectoryName(typeof(Program).Assembly.Location), "glTF");
 
+        public static string ProgramDirectory => System.IO.Path.GetDirectoryName(typeof(Program).Assembly.Location);
+
         #endregion
 
         #region main schema paths
@@ -51,6 +53,11 @@ internal static string VendorExtensionPath(string ext, string json)
             return System.IO.Path.Combine(VendorSchemaDir, ext, "schema", json);
         }
 
+        internal static string CustomExtensionsPath(string ext, string json)
+        {
+            return System.IO.Path.Combine(ProgramDirectory, "Schemas", ext, "schema", json);
+        }
+
         #endregion
 
         #region code generation output paths
diff --git a/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs b/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs
new file mode 100644
index 00000000..b8a20de4
--- /dev/null
+++ b/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs
@@ -0,0 +1,33 @@
+using SharpGLTF.CodeGen;
+using SharpGLTF.SchemaReflection;
+using System.Collections.Generic;
+
+namespace SharpGLTF
+{
+    class ExtInstanceFeaturesExtension : SchemaProcessor
+    {
+        public override string GetTargetProject() { return Constants.CesiumProjectDirectory; }
+
+        private static string RootSchemaUri => Constants.CustomExtensionsPath("EXT_instance_features", "node.EXT_instance_features.schema.json");
+
+        public override void PrepareTypes(CSharpEmitter newEmitter, SchemaType.Context ctx)
+        {
+            newEmitter.SetRuntimeName("EXT_instance_features glTF Node extension", "MeshExtInstanceFeatures");
+            newEmitter.SetRuntimeName("Feature ID in EXT_instance_features", "MeshExtInstanceFeatureID");
+        }
+
+        public override IEnumerable<(string TargetFileName, SchemaType.Context Schema)> Process()
+        {
+            yield return ("Ext.CESIUM_ext_instance_features.g", ProcessNode());
+        }
+
+        private static SchemaType.Context ProcessNode()
+        {
+            var ctx = SchemaProcessing.LoadSchemaContext(RootSchemaUri);
+            ctx.IgnoredByCodeEmitter("glTF Property");
+            ctx.IgnoredByCodeEmitter("glTF Child of Root Property");
+            ctx.IgnoredByCodeEmitter("Texture Info");
+            return ctx;
+        }
+    }
+}
\ No newline at end of file
diff --git a/build/SharpGLTF.CodeGen/Program.cs b/build/SharpGLTF.CodeGen/Program.cs
index 0722c9bb..0ffa1666 100644
--- a/build/SharpGLTF.CodeGen/Program.cs
+++ b/build/SharpGLTF.CodeGen/Program.cs
@@ -21,7 +21,7 @@ static void Main(string[] args)
 
             processors.Add(new MainSchemaProcessor());
 
-            // ---------------------------------------------- Add extensions            
+            //// ---------------------------------------------- Add extensions            
 
             // material extensions       
             processors.Add(new UnlitExtension());
@@ -56,6 +56,8 @@ static void Main(string[] args)
             // other
             processors.Add(new XmpJsonLdExtension());
 
+            processors.Add(new ExtInstanceFeaturesExtension());
+
             // ----------------------------------------------  process all files
 
             foreach (var processor in processors)
diff --git a/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/README.md b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/README.md
new file mode 100644
index 00000000..0f6ec6c9
--- /dev/null
+++ b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/README.md
@@ -0,0 +1,8 @@
+# EXT_instance_features
+
+This directory contains schema's for Cesium extension 
+EXT_instance_features
+
+Specs: https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_instance_features
+
+Schema's are copied from https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_instance_features/schema
diff --git a/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureId.schema.json b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureId.schema.json
new file mode 100644
index 00000000..bc237fcb
--- /dev/null
+++ b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureId.schema.json
@@ -0,0 +1,43 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "featureId.schema.json",
+  "title": "Feature ID in EXT_instance_features",
+  "type": "object",
+  "description": "Feature IDs stored in a GPU mesh instancing attribute",
+  "allOf": [
+    {
+      "$ref": "glTFProperty.schema.json"
+    }
+  ],
+  "properties": {
+    "featureCount": {
+      "type": "integer",
+      "minimum": 1,
+      "description": "The number of unique features in the attribute."
+    },
+    "nullFeatureId": {
+      "type": "integer",
+      "minimum": 0,
+      "description": "A value that indicates that no feature is associated with this instance."
+    },
+    "label": {
+      "type": "string",
+      "pattern": "^[a-zA-Z_][a-zA-Z0-9_]*$",
+      "description": "A label assigned to this feature ID set. Labels must be alphanumeric identifiers matching the regular expression `^[a-zA-Z_][a-zA-Z0-9_]*$`."
+    },
+    "attribute": {
+      "description": "An attribute containing feature IDs. When this is omitted, then the feature IDs are assigned to the GPU instances by their index.",
+      "$ref": "featureIdAttribute.schema.json"
+    },
+    "propertyTable": {
+      "type": "integer",
+      "minimum": 0,
+      "description": "The index of the property table containing per-feature property values. Only applicable when using the `EXT_structural_metadata` extension."
+    },
+    "extensions": {},
+    "extras": {}
+  },
+  "required": [
+    "featureCount"
+  ]
+}
\ No newline at end of file
diff --git a/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureIdAttribute.schema.json b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureIdAttribute.schema.json
new file mode 100644
index 00000000..6e1bc8d2
--- /dev/null
+++ b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/featureIdAttribute.schema.json
@@ -0,0 +1,8 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "featureIdAttribute.schema.json",
+  "title": "Feature ID Attribute in EXT_instance_features",
+  "type": "integer",
+  "minimum": 0,
+  "description": "An integer value used to construct a string in the format `_FEATURE_ID_<set index>` which is a reference to a key in `EXT_mesh_gpu_instancing.attributes` dictionary (e.g. a value of `0` corresponds to `_FEATURE_ID_0`)."
+}
\ No newline at end of file
diff --git a/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/node.EXT_instance_features.schema.json b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/node.EXT_instance_features.schema.json
new file mode 100644
index 00000000..d49f6d97
--- /dev/null
+++ b/build/SharpGLTF.CodeGen/Schemas/EXT_instance_features/schema/node.EXT_instance_features.schema.json
@@ -0,0 +1,27 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "node.EXT_instance_features.schema.json",
+  "title": "EXT_instance_features glTF Node extension",
+  "type": "object",
+  "description": "An object describing per-instance feature IDs.",
+  "allOf": [
+    {
+      "$ref": "glTFProperty.schema.json"
+    }
+  ],
+  "properties": {
+    "featureIds": {
+      "type": "array",
+      "description": "An array of feature ID sets.",
+      "minItems": 1,
+      "items": {
+        "$ref": "featureId.schema.json"
+      }
+    },
+    "extensions": {},
+    "extras": {}
+  },
+  "required": [
+    "featureIds"
+  ]
+}
\ No newline at end of file
diff --git a/build/SharpGLTF.CodeGen/SharpGLTF.CodeGen.csproj b/build/SharpGLTF.CodeGen/SharpGLTF.CodeGen.csproj
index 54a037ab..92936f5e 100644
--- a/build/SharpGLTF.CodeGen/SharpGLTF.CodeGen.csproj
+++ b/build/SharpGLTF.CodeGen/SharpGLTF.CodeGen.csproj
@@ -11,4 +11,16 @@
     <PackageReference Include="NJsonSchema.CodeGeneration.CSharp" Version="10.9.0" />
   </ItemGroup>
 
+  <ItemGroup>
+    <None Update="Schemas\EXT_instance_features\schema\featureId.schema.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+    <None Update="Schemas\EXT_instance_features\schema\featureIdAttribute.schema.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+    <None Update="Schemas\EXT_instance_features\schema\node.EXT_instance_features.schema.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
 </Project>
diff --git a/src/SharpGLTF.Cesium/Schema2/CesiumExtensions.cs b/src/SharpGLTF.Cesium/Schema2/CesiumExtensions.cs
index c013bf5f..83f3bee2 100644
--- a/src/SharpGLTF.Cesium/Schema2/CesiumExtensions.cs
+++ b/src/SharpGLTF.Cesium/Schema2/CesiumExtensions.cs
@@ -21,6 +21,7 @@ public static void RegisterExtensions()
             _CesiumRegistered = true;
 
             ExtensionsFactory.RegisterExtension<MeshPrimitive, CesiumPrimitiveOutline>("CESIUM_primitive_outline");
+            ExtensionsFactory.RegisterExtension<Node, MeshExtInstanceFeatures>("EXT_instance_features");
         }
     }
 }
diff --git a/src/SharpGLTF.Cesium/Schema2/Generated/Ext.CESIUM_ext_instance_features.g.cs b/src/SharpGLTF.Cesium/Schema2/Generated/Ext.CESIUM_ext_instance_features.g.cs
new file mode 100644
index 00000000..14f20c7b
--- /dev/null
+++ b/src/SharpGLTF.Cesium/Schema2/Generated/Ext.CESIUM_ext_instance_features.g.cs
@@ -0,0 +1,110 @@
+// <auto-generated/>
+
+//------------------------------------------------------------------------------------------------
+//      This file has been programatically generated; DON´T EDIT!
+//------------------------------------------------------------------------------------------------
+
+#pragma warning disable SA1001
+#pragma warning disable SA1027
+#pragma warning disable SA1028
+#pragma warning disable SA1121
+#pragma warning disable SA1205
+#pragma warning disable SA1309
+#pragma warning disable SA1402
+#pragma warning disable SA1505
+#pragma warning disable SA1507
+#pragma warning disable SA1508
+#pragma warning disable SA1652
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Numerics;
+using System.Text.Json;
+
+namespace SharpGLTF.Schema2
+{
+	using Collections;
+
+	/// <summary>
+	/// Feature IDs stored in a GPU mesh instancing attribute
+	/// </summary>
+	#if NET6_0_OR_GREATER
+	[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
+	#endif
+	[global::System.CodeDom.Compiler.GeneratedCodeAttribute("SharpGLTF.CodeGen", "1.0.0.0")]
+	partial class MeshExtInstanceFeatureID : ExtraProperties
+	{
+	
+		private Int32? _attribute;
+		
+		private const Int32 _featureCountMinimum = 1;
+		private Int32 _featureCount;
+		
+		private String _label;
+		
+		private const Int32 _nullFeatureIdMinimum = 0;
+		private Int32? _nullFeatureId;
+		
+		private const Int32 _propertyTableMinimum = 0;
+		private Int32? _propertyTable;
+		
+	
+		protected override void SerializeProperties(Utf8JsonWriter writer)
+		{
+			base.SerializeProperties(writer);
+			SerializeProperty(writer, "attribute", _attribute);
+			SerializeProperty(writer, "featureCount", _featureCount);
+			SerializeProperty(writer, "label", _label);
+			SerializeProperty(writer, "nullFeatureId", _nullFeatureId);
+			SerializeProperty(writer, "propertyTable", _propertyTable);
+		}
+	
+		protected override void DeserializeProperty(string jsonPropertyName, ref Utf8JsonReader reader)
+		{
+			switch (jsonPropertyName)
+			{
+				case "attribute": _attribute = DeserializePropertyValue<Int32?>(ref reader); break;
+				case "featureCount": _featureCount = DeserializePropertyValue<Int32>(ref reader); break;
+				case "label": _label = DeserializePropertyValue<String>(ref reader); break;
+				case "nullFeatureId": _nullFeatureId = DeserializePropertyValue<Int32?>(ref reader); break;
+				case "propertyTable": _propertyTable = DeserializePropertyValue<Int32?>(ref reader); break;
+				default: base.DeserializeProperty(jsonPropertyName,ref reader); break;
+			}
+		}
+	
+	}
+
+	/// <summary>
+	/// An object describing per-instance feature IDs.
+	/// </summary>
+	#if NET6_0_OR_GREATER
+	[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
+	#endif
+	[global::System.CodeDom.Compiler.GeneratedCodeAttribute("SharpGLTF.CodeGen", "1.0.0.0")]
+	partial class MeshExtInstanceFeatures : ExtraProperties
+	{
+	
+		private const int _featureIdsMinItems = 1;
+		private List<MeshExtInstanceFeatureID> _featureIds;
+		
+	
+		protected override void SerializeProperties(Utf8JsonWriter writer)
+		{
+			base.SerializeProperties(writer);
+			SerializeProperty(writer, "featureIds", _featureIds, _featureIdsMinItems);
+		}
+	
+		protected override void DeserializeProperty(string jsonPropertyName, ref Utf8JsonReader reader)
+		{
+			switch (jsonPropertyName)
+			{
+				case "featureIds": DeserializePropertyList<MeshExtInstanceFeatureID>(ref reader, _featureIds); break;
+				default: base.DeserializeProperty(jsonPropertyName,ref reader); break;
+			}
+		}
+	
+	}
+
+}
diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
new file mode 100644
index 00000000..9e7e76d4
--- /dev/null
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
@@ -0,0 +1,63 @@
+using SharpGLTF.Validation;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace SharpGLTF.Schema2
+{
+    public partial class MeshExtInstanceFeatures
+    {
+        private Node  _node;
+        internal MeshExtInstanceFeatures(Node node)
+        {
+            _node = node;
+            _featureIds = new List<MeshExtInstanceFeatureID>();
+        }
+
+        public List<MeshExtInstanceFeatureID> FeatureIds
+        {
+            get
+            {
+                return _featureIds;
+            }
+            set
+            {
+                if (value == null) { _featureIds = null; return; }
+
+                _featureIds = value;
+            }
+        }
+
+        protected override void OnValidateContent(ValidationContext validate)
+        {
+            var extInstanceFeatures = (MeshExtInstanceFeatures)_node.Extensions.FirstOrDefault();
+
+            validate.NotNull(nameof(FeatureIds), extInstanceFeatures.FeatureIds);
+            validate.IsTrue(nameof(FeatureIds), extInstanceFeatures.FeatureIds.Count > 0, "Instance FeatureIds has items");
+
+            base.OnValidateContent(validate);
+        }
+    }
+
+    public partial class MeshExtInstanceFeatureID
+    {
+        public MeshExtInstanceFeatureID(int featureCount, int? attribute = null, int? propertyTable = null, string label = null, int? nullFeatureId = null)
+        {
+            _featureCount = featureCount;
+            _attribute = attribute;
+            _label = label;
+            _propertyTable = propertyTable;
+            _nullFeatureId = nullFeatureId;
+        }
+    }
+
+    public static class ExtInstanceFeatures
+    {
+        public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID> list)
+        {
+            if (list == null) { node.RemoveExtensions<MeshExtInstanceFeatures>(); return; }
+
+            var ext = node.UseExtension<MeshExtInstanceFeatures>();
+            ext.FeatureIds = list;
+        }
+    }
+}
diff --git a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
new file mode 100644
index 00000000..cce1d25a
--- /dev/null
+++ b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
@@ -0,0 +1,65 @@
+using NUnit.Framework;
+using SharpGLTF.Geometry;
+using SharpGLTF.Geometry.VertexTypes;
+using SharpGLTF.Materials;
+using SharpGLTF.Scenes;
+using SharpGLTF.Schema2;
+using SharpGLTF.Validation;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+
+namespace SharpGLTF.Cesium
+{
+    [Category("Toolkit.Scenes")]
+    public class ExtInstanceFeaturesTests
+    {
+        [SetUp]
+        public void SetUp()
+        {
+            CesiumExtensions.RegisterExtensions();
+        }
+
+        [Test(Description = "Creates a simple triangle with Cesium EXT_Instance_Features")]
+        public void AddExtInstanceFeatures()
+        {
+            TestContext.CurrentContext.AttachGltfValidatorLinks();
+
+            // todo: create a test with ext_mesh_gpu_instancing
+
+            var material = MaterialBuilder.CreateDefault();
+
+            var mesh = new MeshBuilder<VertexPosition>("mesh");
+
+            var prim = mesh.UsePrimitive(material);
+            prim.AddTriangle(new VertexPosition(-10, 0, 0), new VertexPosition(10, 0, 0), new VertexPosition(0, 10, 0));
+
+            var scene = new SceneBuilder();
+
+            scene.AddRigidMesh(mesh, Matrix4x4.Identity);
+
+            var model = scene.ToGltf2();
+
+            // following the sample at https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_instance_features#feature-id-by-gpu-instance
+            var featureId0 = new MeshExtInstanceFeatureID(2, 0, 0, "Forests",2);
+            var featureId1 = new MeshExtInstanceFeatureID(9, propertyTable: 1, label: "Trees");
+
+            var featureIds = new List<MeshExtInstanceFeatureID>() { featureId0, featureId1 };
+            model.LogicalNodes[0].SetFeatureIds(featureIds);
+
+            var cesiumExtInstanceFeaturesExtension = (MeshExtInstanceFeatures)model.LogicalNodes[0].Extensions.FirstOrDefault();
+            Assert.NotNull(cesiumExtInstanceFeaturesExtension.FeatureIds);
+
+            Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds.Equals(featureIds));
+            Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds[0].Equals(featureId0));
+            Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds[1].Equals(featureId1));
+
+            var ctx = new ValidationResult(model, ValidationMode.Strict, true);
+            model.ValidateContent(ctx.GetContext());
+
+            scene.AttachToCurrentTest("cesium_ext_instance_features.glb");
+            scene.AttachToCurrentTest("cesium_ext_instance_features.gltf");
+            scene.AttachToCurrentTest("cesium_ext_instance_features.plotly");
+        }
+    }
+}

From f16732d15c913f6e0c982a6f09d0da3a703812aa Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 13:49:32 +0100
Subject: [PATCH 02/14] undo commenting

---
 build/SharpGLTF.CodeGen/Program.cs | 72 +++++++++++++++---------------
 1 file changed, 36 insertions(+), 36 deletions(-)

diff --git a/build/SharpGLTF.CodeGen/Program.cs b/build/SharpGLTF.CodeGen/Program.cs
index 38a2ca92..655b1f24 100644
--- a/build/SharpGLTF.CodeGen/Program.cs
+++ b/build/SharpGLTF.CodeGen/Program.cs
@@ -23,42 +23,42 @@ static void Main(string[] args)
 
             processors.Add(new MainSchemaProcessor());
 
-            //// ---------------------------------------------- Add extensions            
-
-            //// material extensions       
-            //processors.Add(new UnlitExtension());
-            //processors.Add(new IorExtension());
-            //processors.Add(new SheenExtension());
-            //processors.Add(new VolumeExtension());
-            //processors.Add(new SpecularExtension());
-            //processors.Add(new ClearCoatExtension());
-            //processors.Add(new IridescenceExtension());
-            //processors.Add(new TransmissionExtension());
-            //processors.Add(new EmissiveStrengthExtension());
-            //processors.Add(new SpecularGlossinessExtension());
-
-            //// cesium outlines
-            //processors.Add(new CesiumPrimitiveOutlineExtension());
-
-            //// lights
-            //processors.Add(new LightsPunctualExtension());
-
-            //// gpu mesh instancing
-            //processors.Add(new MeshGpuInstancingExtension());
-
-            //// textures
-            //processors.Add(new TextureTransformExtension());
-            //processors.Add(new TextureDDSExtension());
-            //processors.Add(new TextureWebpExtension());
-            //processors.Add(new TextureKtx2Extension());
-
-            //processors.Add(new AgiArticulationsExtension());
-            //processors.Add(new AgiStkMetadataExtension());
-
-            //// other
-            //processors.Add(new XmpJsonLdExtension());
-
-            //processors.Add(new ExtMeshFeaturesExtension());
+            // ---------------------------------------------- Add extensions            
+
+            // material extensions       
+            processors.Add(new UnlitExtension());
+            processors.Add(new IorExtension());
+            processors.Add(new SheenExtension());
+            processors.Add(new VolumeExtension());
+            processors.Add(new SpecularExtension());
+            processors.Add(new ClearCoatExtension());
+            processors.Add(new IridescenceExtension());
+            processors.Add(new TransmissionExtension());
+            processors.Add(new EmissiveStrengthExtension());
+            processors.Add(new SpecularGlossinessExtension());
+
+            // cesium outlines
+            processors.Add(new CesiumPrimitiveOutlineExtension());
+
+            // lights
+            processors.Add(new LightsPunctualExtension());
+
+            // gpu mesh instancing
+            processors.Add(new MeshGpuInstancingExtension());
+
+            // textures
+            processors.Add(new TextureTransformExtension());
+            processors.Add(new TextureDDSExtension());
+            processors.Add(new TextureWebpExtension());
+            processors.Add(new TextureKtx2Extension());
+
+            processors.Add(new AgiArticulationsExtension());
+            processors.Add(new AgiStkMetadataExtension());
+
+            // other
+            processors.Add(new XmpJsonLdExtension());
+
+            processors.Add(new ExtMeshFeaturesExtension());
 
             processors.Add(new ExtInstanceFeaturesExtension());
 

From 8fbe6072966e162e6ca789f00978d17bfff57961 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 15:36:22 +0100
Subject: [PATCH 03/14] add validation and guards

---
 .../Schema2/MeshExtInstanceFeatures.cs        | 72 +++++++++++++++++--
 1 file changed, 68 insertions(+), 4 deletions(-)

diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
index 9e7e76d4..844e7338 100644
--- a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
@@ -6,7 +6,7 @@ namespace SharpGLTF.Schema2
 {
     public partial class MeshExtInstanceFeatures
     {
-        private Node  _node;
+        private Node _node;
         internal MeshExtInstanceFeatures(Node node)
         {
             _node = node;
@@ -48,16 +48,80 @@ public MeshExtInstanceFeatureID(int featureCount, int? attribute = null, int? pr
             _propertyTable = propertyTable;
             _nullFeatureId = nullFeatureId;
         }
+
+        /// <summary>
+        /// The number of unique features in the attribute
+        /// </summary>
+        public int FeatureCount { get => _featureCount; }
+
+        /// <summary>
+        /// An attribute containing feature IDs. When this is omitted, then the feature IDs are assigned to the GPU instances by their index.
+        /// </summary>
+        public int? Attribute { get => _attribute; }
+
+        /// <summary>
+        /// A label assigned to this feature ID set
+        /// </summary>
+        public string Label { get => _label; }
+
+        /// <summary>
+        /// The index of the property table containing per-feature property values. Only applicable when using the `EXT_structural_metadata` extension.
+        /// </summary>
+        public int? PropertyTable { get => _propertyTable; }
+
+        /// <summary>
+        /// A value that indicates that no feature is associated with this instance
+        /// </summary>
+        public int? NullFeatureId { get => _nullFeatureId; }
     }
 
     public static class ExtInstanceFeatures
     {
-        public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID> list)
+        /// <summary>
+        /// Set the instance feature ids for this node.
+        /// </summary>
+        /// <param name="node"></param>
+        /// <param name="instanceFeatureIds"></param>
+        public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID> instanceFeatureIds)
         {
-            if (list == null) { node.RemoveExtensions<MeshExtInstanceFeatures>(); return; }
+            if (instanceFeatureIds == null) { node.RemoveExtensions<MeshExtInstanceFeatures>(); return; }
+
+            Guard.NotNullOrEmpty(instanceFeatureIds, nameof(instanceFeatureIds));
+
+            foreach (var instanceFeatureId in instanceFeatureIds)
+            {
+                ValidateInstanceFeatureId(node, instanceFeatureId);
+            };
 
             var ext = node.UseExtension<MeshExtInstanceFeatures>();
-            ext.FeatureIds = list;
+            ext.FeatureIds = instanceFeatureIds;
+        }
+
+        private static void ValidateInstanceFeatureId(Node node, MeshExtInstanceFeatureID item)
+        {
+            Guard.MustBeGreaterThanOrEqualTo((int)item.FeatureCount, 1, nameof(item.FeatureCount));
+
+            if (item.NullFeatureId.HasValue)
+            {
+                Guard.MustBeGreaterThanOrEqualTo((int)item.NullFeatureId, 0, nameof(item.NullFeatureId));
+            }
+            if (item.Label != null)
+            {
+                var regex = "^[a-zA-Z_][a-zA-Z0-9_]*$";
+                Guard.IsTrue(System.Text.RegularExpressions.Regex.IsMatch(item.Label, regex), nameof(item.Label));
+            }
+            if (item.Attribute.HasValue)
+            {
+                Guard.MustBeGreaterThanOrEqualTo((int)item.Attribute, 0, nameof(item.Attribute));
+                // todo: check attribute
+                // Guard that the custom vertex attribute (_FEATURE_ID_{attribute}) exists when FeatureID has attribute set
+                // var expectedVertexAttribute = $"_FEATURE_ID_{item.Attribute}";
+                // Guard.NotNull(primitive.GetVertexAccessor(expectedVertexAttribute), expectedVertexAttribute);
+            }
+            if (item.PropertyTable.HasValue)
+            {
+                Guard.MustBeGreaterThanOrEqualTo((int)item.PropertyTable, 0, nameof(item.PropertyTable));
+            }
         }
     }
 }

From ce996e690ee01200fcd5f525b7b9ece17f7d4944 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 16:19:42 +0100
Subject: [PATCH 04/14] create test with gpu instancing and
 ext_instance_features

---
 .../Schema2/MeshExtInstanceFeatures.cs        |   6 ++-
 .../ExtInstanceFeaturesTests.cs               |  47 +++++++++---------
 .../SharpGLTF.Cesium.Tests.csproj             |   6 +++
 tests/SharpGLTF.Cesium.Tests/tree.glb         | Bin 0 -> 20220 bytes
 4 files changed, 35 insertions(+), 24 deletions(-)
 create mode 100644 tests/SharpGLTF.Cesium.Tests/tree.glb

diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
index 844e7338..762b97c0 100644
--- a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
@@ -29,7 +29,7 @@ public List<MeshExtInstanceFeatureID> FeatureIds
 
         protected override void OnValidateContent(ValidationContext validate)
         {
-            var extInstanceFeatures = (MeshExtInstanceFeatures)_node.Extensions.FirstOrDefault();
+            var extInstanceFeatures = (MeshExtInstanceFeatures)_node.Extensions.Where(item => item is MeshExtInstanceFeatures).FirstOrDefault();
 
             validate.NotNull(nameof(FeatureIds), extInstanceFeatures.FeatureIds);
             validate.IsTrue(nameof(FeatureIds), extInstanceFeatures.FeatureIds.Count > 0, "Instance FeatureIds has items");
@@ -40,6 +40,10 @@ protected override void OnValidateContent(ValidationContext validate)
 
     public partial class MeshExtInstanceFeatureID
     {
+        public MeshExtInstanceFeatureID()
+        {
+        }
+
         public MeshExtInstanceFeatureID(int featureCount, int? attribute = null, int? propertyTable = null, string label = null, int? nullFeatureId = null)
         {
             _featureCount = featureCount;
diff --git a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
index cce1d25a..52a35eba 100644
--- a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
+++ b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
@@ -1,13 +1,12 @@
 using NUnit.Framework;
-using SharpGLTF.Geometry;
-using SharpGLTF.Geometry.VertexTypes;
-using SharpGLTF.Materials;
 using SharpGLTF.Scenes;
 using SharpGLTF.Schema2;
+using SharpGLTF.Transforms;
 using SharpGLTF.Validation;
 using System.Collections.Generic;
 using System.Linq;
 using System.Numerics;
+using System.Text.Json.Nodes;
 
 namespace SharpGLTF.Cesium
 {
@@ -21,33 +20,35 @@ public void SetUp()
         }
 
         [Test(Description = "Creates a simple triangle with Cesium EXT_Instance_Features")]
-        public void AddExtInstanceFeatures()
+        public void AddExtGpuInstanceFeatures()
         {
-            TestContext.CurrentContext.AttachGltfValidatorLinks();
+            var settings = SceneBuilderSchema2Settings.WithGpuInstancing;
+            settings.GpuMeshInstancingMinCount = 0;
 
-            // todo: create a test with ext_mesh_gpu_instancing
+            var modelRoot = ModelRoot.Load(ResourceInfo.From("tree.glb"));
+            var meshBuilder = modelRoot.LogicalMeshes.First().ToMeshBuilder();
+            var sceneBuilder = new SceneBuilder();
+            var quaternion = Quaternion.CreateFromYawPitchRoll(0, 0, 0);
+            var scale = Vector3.One;
 
-            var material = MaterialBuilder.CreateDefault();
+            sceneBuilder.
+                    AddRigidMesh(meshBuilder, new AffineTransform(scale, quaternion, new Vector3(-10, 0, 10))).
+                    WithExtras(JsonNode.Parse("{\"_FEATURE_ID_0\":0}"));
+            sceneBuilder.
+                    AddRigidMesh(meshBuilder, new AffineTransform(scale, quaternion, new Vector3(0, 0, 0))).
+                    WithExtras(JsonNode.Parse("{\"_FEATURE_ID_0\":1}"));
 
-            var mesh = new MeshBuilder<VertexPosition>("mesh");
 
-            var prim = mesh.UsePrimitive(material);
-            prim.AddTriangle(new VertexPosition(-10, 0, 0), new VertexPosition(10, 0, 0), new VertexPosition(0, 10, 0));
-
-            var scene = new SceneBuilder();
-
-            scene.AddRigidMesh(mesh, Matrix4x4.Identity);
-
-            var model = scene.ToGltf2();
-
-            // following the sample at https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_instance_features#feature-id-by-gpu-instance
-            var featureId0 = new MeshExtInstanceFeatureID(2, 0, 0, "Forests",2);
+            var featureId0 = new MeshExtInstanceFeatureID(2, 0, 0, "Forests", 2);
             var featureId1 = new MeshExtInstanceFeatureID(9, propertyTable: 1, label: "Trees");
 
             var featureIds = new List<MeshExtInstanceFeatureID>() { featureId0, featureId1 };
+
+            var model = sceneBuilder.ToGltf2(settings);
             model.LogicalNodes[0].SetFeatureIds(featureIds);
 
-            var cesiumExtInstanceFeaturesExtension = (MeshExtInstanceFeatures)model.LogicalNodes[0].Extensions.FirstOrDefault();
+            var cesiumExtInstanceFeaturesExtension = (MeshExtInstanceFeatures)model.LogicalNodes[0].Extensions.Where(item => item is MeshExtInstanceFeatures).FirstOrDefault();
+
             Assert.NotNull(cesiumExtInstanceFeaturesExtension.FeatureIds);
 
             Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds.Equals(featureIds));
@@ -57,9 +58,9 @@ public void AddExtInstanceFeatures()
             var ctx = new ValidationResult(model, ValidationMode.Strict, true);
             model.ValidateContent(ctx.GetContext());
 
-            scene.AttachToCurrentTest("cesium_ext_instance_features.glb");
-            scene.AttachToCurrentTest("cesium_ext_instance_features.gltf");
-            scene.AttachToCurrentTest("cesium_ext_instance_features.plotly");
+            model.AttachToCurrentTest("cesium_ext_instance_features.glb");
+            model.AttachToCurrentTest("cesium_ext_instance_features.gltf");
+            model.AttachToCurrentTest("cesium_ext_instance_features.plotly");
         }
     }
 }
diff --git a/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj b/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
index c7295562..5639682d 100644
--- a/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
+++ b/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
@@ -20,4 +20,10 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
   </ItemGroup>
 
+  <ItemGroup>
+    <None Update="tree.glb">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
 </Project>
diff --git a/tests/SharpGLTF.Cesium.Tests/tree.glb b/tests/SharpGLTF.Cesium.Tests/tree.glb
new file mode 100644
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Aa{vGU

literal 0
HcmV?d00001


From e3e88b4ecbd19fdb773749d66e6b50fb016edb34 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 16:48:40 +0100
Subject: [PATCH 05/14] github actions to .net 8

---
 .github/workflows/dotnet.yml                               | 2 +-
 src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs        | 3 ++-
 tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/dotnet.yml b/.github/workflows/dotnet.yml
index bd76993b..d1425feb 100644
--- a/.github/workflows/dotnet.yml
+++ b/.github/workflows/dotnet.yml
@@ -8,7 +8,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        dotnet-version: [ '6.0.x' ]
+        dotnet-version: [ '8.0.x' ]
         os: [windows-latest, ubuntu-latest, macos-latest]
 
     steps:
diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs
index 693b6164..0912c45f 100644
--- a/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs
@@ -1,6 +1,7 @@
 using SharpGLTF.Validation;
 using System.Collections.Generic;
 using System.Linq;
+using System.Xml.Linq;
 
 namespace SharpGLTF.Schema2
 {
@@ -26,7 +27,7 @@ public List<MeshExtMeshFeatureID> FeatureIds
 
         protected override void OnValidateContent(ValidationContext validate)
         {
-            var extMeshFeatures = (MeshExtMeshFeatures)_meshPrimitive.Extensions.FirstOrDefault();
+            var extMeshFeatures = (MeshExtMeshFeatures)_meshPrimitive.Extensions.Where(item => item is MeshExtMeshFeatures).FirstOrDefault();
 
             validate.NotNull(nameof(FeatureIds), extMeshFeatures.FeatureIds);
             validate.IsTrue(nameof(FeatureIds), extMeshFeatures.FeatureIds.Count > 0, "FeatureIds has items");
diff --git a/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj b/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
index 5639682d..b45f4a6c 100644
--- a/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
+++ b/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFrameworks>net471;net8.0-windows</TargetFrameworks>

From 6fd314cc00b3be63b26f9c9252300a95a897f11a Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 17:04:19 +0100
Subject: [PATCH 06/14] add check for instance vertex accessor

---
 .../Schema2/MeshExtInstanceFeatures.cs        | 28 +++++++++----------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
index 762b97c0..2a14a9af 100644
--- a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
@@ -101,30 +101,30 @@ public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID>
             ext.FeatureIds = instanceFeatureIds;
         }
 
-        private static void ValidateInstanceFeatureId(Node node, MeshExtInstanceFeatureID item)
+        private static void ValidateInstanceFeatureId(Node node, MeshExtInstanceFeatureID instanceFeatureId)
         {
-            Guard.MustBeGreaterThanOrEqualTo((int)item.FeatureCount, 1, nameof(item.FeatureCount));
+            Guard.MustBeGreaterThanOrEqualTo((int)instanceFeatureId.FeatureCount, 1, nameof(instanceFeatureId.FeatureCount));
 
-            if (item.NullFeatureId.HasValue)
+            if (instanceFeatureId.NullFeatureId.HasValue)
             {
-                Guard.MustBeGreaterThanOrEqualTo((int)item.NullFeatureId, 0, nameof(item.NullFeatureId));
+                Guard.MustBeGreaterThanOrEqualTo((int)instanceFeatureId.NullFeatureId, 0, nameof(instanceFeatureId.NullFeatureId));
             }
-            if (item.Label != null)
+            if (instanceFeatureId.Label != null)
             {
                 var regex = "^[a-zA-Z_][a-zA-Z0-9_]*$";
-                Guard.IsTrue(System.Text.RegularExpressions.Regex.IsMatch(item.Label, regex), nameof(item.Label));
+                Guard.IsTrue(System.Text.RegularExpressions.Regex.IsMatch(instanceFeatureId.Label, regex), nameof(instanceFeatureId.Label));
             }
-            if (item.Attribute.HasValue)
+            if (instanceFeatureId.Attribute.HasValue)
             {
-                Guard.MustBeGreaterThanOrEqualTo((int)item.Attribute, 0, nameof(item.Attribute));
-                // todo: check attribute
-                // Guard that the custom vertex attribute (_FEATURE_ID_{attribute}) exists when FeatureID has attribute set
-                // var expectedVertexAttribute = $"_FEATURE_ID_{item.Attribute}";
-                // Guard.NotNull(primitive.GetVertexAccessor(expectedVertexAttribute), expectedVertexAttribute);
+                Guard.MustBeGreaterThanOrEqualTo((int)instanceFeatureId.Attribute, 0, nameof(instanceFeatureId.Attribute));
+                var expectedVertexAttribute = $"_FEATURE_ID_{instanceFeatureId.Attribute}";
+                var gpuInstancing = node.GetGpuInstancing();
+                var featureIdAccessors = gpuInstancing.GetAccessor(expectedVertexAttribute);
+                Guard.NotNull(featureIdAccessors, expectedVertexAttribute);
             }
-            if (item.PropertyTable.HasValue)
+            if (instanceFeatureId.PropertyTable.HasValue)
             {
-                Guard.MustBeGreaterThanOrEqualTo((int)item.PropertyTable, 0, nameof(item.PropertyTable));
+                Guard.MustBeGreaterThanOrEqualTo((int)instanceFeatureId.PropertyTable, 0, nameof(instanceFeatureId.PropertyTable));
             }
         }
     }

From 99ad1920297bd698c3a602af84b650603c69e90f Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 17:51:11 +0100
Subject: [PATCH 07/14] add some more checks for gpu_instancing

---
 .../Schema2/MeshExtInstanceFeatures.cs             | 14 +++++++++++---
 .../Schema2/MeshExtMeshFeatures.cs                 |  9 +++++----
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
index 2a14a9af..12c36ee1 100644
--- a/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtInstanceFeatures.cs
@@ -1,6 +1,7 @@
 using SharpGLTF.Validation;
 using System.Collections.Generic;
 using System.Linq;
+using System.Xml.Linq;
 
 namespace SharpGLTF.Schema2
 {
@@ -29,10 +30,14 @@ public List<MeshExtInstanceFeatureID> FeatureIds
 
         protected override void OnValidateContent(ValidationContext validate)
         {
-            var extInstanceFeatures = (MeshExtInstanceFeatures)_node.Extensions.Where(item => item is MeshExtInstanceFeatures).FirstOrDefault();
+            var extInstanceFeatures = _node.Extensions.Where(item => item is MeshExtInstanceFeatures).FirstOrDefault();
+            validate.NotNull(nameof(extInstanceFeatures), extInstanceFeatures);
+            var ext = (MeshExtInstanceFeatures)extInstanceFeatures;
+            var extMeshGpInstancing = _node.Extensions.Where(item => item is MeshGpuInstancing).FirstOrDefault();
+            validate.NotNull(nameof(extMeshGpInstancing), extMeshGpInstancing);
 
-            validate.NotNull(nameof(FeatureIds), extInstanceFeatures.FeatureIds);
-            validate.IsTrue(nameof(FeatureIds), extInstanceFeatures.FeatureIds.Count > 0, "Instance FeatureIds has items");
+            validate.NotNull(nameof(FeatureIds), ext.FeatureIds);
+            validate.IsTrue(nameof(FeatureIds), ext.FeatureIds.Count > 0, "Instance FeatureIds has items");
 
             base.OnValidateContent(validate);
         }
@@ -92,6 +97,9 @@ public static void SetFeatureIds(this Node node, List<MeshExtInstanceFeatureID>
 
             Guard.NotNullOrEmpty(instanceFeatureIds, nameof(instanceFeatureIds));
 
+            var extMeshGpInstancing = node.Extensions.Where(item => item is MeshGpuInstancing).FirstOrDefault();
+            Guard.NotNull(extMeshGpInstancing, nameof(extMeshGpInstancing));
+
             foreach (var instanceFeatureId in instanceFeatureIds)
             {
                 ValidateInstanceFeatureId(node, instanceFeatureId);
diff --git a/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs b/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs
index 0912c45f..a20c7ce3 100644
--- a/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs
+++ b/src/SharpGLTF.Cesium/Schema2/MeshExtMeshFeatures.cs
@@ -27,10 +27,11 @@ public List<MeshExtMeshFeatureID> FeatureIds
 
         protected override void OnValidateContent(ValidationContext validate)
         {
-            var extMeshFeatures = (MeshExtMeshFeatures)_meshPrimitive.Extensions.Where(item => item is MeshExtMeshFeatures).FirstOrDefault();
-
-            validate.NotNull(nameof(FeatureIds), extMeshFeatures.FeatureIds);
-            validate.IsTrue(nameof(FeatureIds), extMeshFeatures.FeatureIds.Count > 0, "FeatureIds has items");
+            var extMeshFeatures = _meshPrimitive.Extensions.Where(item => item is MeshExtMeshFeatures).FirstOrDefault();
+            validate.NotNull(nameof(extMeshFeatures), extMeshFeatures);
+            var ext = (MeshExtMeshFeatures)extMeshFeatures;
+            validate.NotNull(nameof(FeatureIds), ext.FeatureIds);
+            validate.IsTrue(nameof(FeatureIds), ext.FeatureIds.Count > 0, "FeatureIds has items");
 
             base.OnValidateContent(validate);
         }

From 8778d145e8e95af8fc1217e29a51c9b9c6c9cc57 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 17:55:54 +0100
Subject: [PATCH 08/14] update comment

---
 tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
index 52a35eba..e90b1b06 100644
--- a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
+++ b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
@@ -19,7 +19,7 @@ public void SetUp()
             CesiumExtensions.RegisterExtensions();
         }
 
-        [Test(Description = "Creates a simple triangle with Cesium EXT_Instance_Features")]
+        [Test(Description = "Creates a gpu_instancing glTF from a tree with Cesium EXT_Instance_Features")]
         public void AddExtGpuInstanceFeatures()
         {
             var settings = SceneBuilderSchema2Settings.WithGpuInstancing;

From d66c03b148eb85c830fe08161dd360dea2150b51 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 19:24:53 +0100
Subject: [PATCH 09/14] Update SharpGLTF.Cesium.Tests.csproj

---
 tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj b/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
index b45f4a6c..b7f52163 100644
--- a/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
+++ b/tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net471;net8.0-windows</TargetFrameworks>
+    <TargetFrameworks>net471;net6.0-windows;net8.0-windows</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <RootNamespace>SharpGLTF</RootNamespace>
     <LangVersion>latest</LangVersion>

From 603a458eeb6429d929be4ccdba6276d6fae7a13a Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 19:25:14 +0100
Subject: [PATCH 10/14] Update dotnet.yml

---
 .github/workflows/dotnet.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/dotnet.yml b/.github/workflows/dotnet.yml
index d1425feb..bd76993b 100644
--- a/.github/workflows/dotnet.yml
+++ b/.github/workflows/dotnet.yml
@@ -8,7 +8,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        dotnet-version: [ '8.0.x' ]
+        dotnet-version: [ '6.0.x' ]
         os: [windows-latest, ubuntu-latest, macos-latest]
 
     steps:

From db8d1c83aabd012af781b72ac49171fde703f973 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Mon, 27 Nov 2023 19:32:18 +0100
Subject: [PATCH 11/14] Update dotnet.yml

---
 .github/workflows/dotnet.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/dotnet.yml b/.github/workflows/dotnet.yml
index bd76993b..d1425feb 100644
--- a/.github/workflows/dotnet.yml
+++ b/.github/workflows/dotnet.yml
@@ -8,7 +8,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        dotnet-version: [ '6.0.x' ]
+        dotnet-version: [ '8.0.x' ]
         os: [windows-latest, ubuntu-latest, macos-latest]
 
     steps:

From 233b0baca6e93e41f403e0608b557d32e5d68e67 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Wed, 29 Nov 2023 22:38:16 +0100
Subject: [PATCH 12/14] Update Ext.EXT_InstanceFeatures.cs

---
 build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs b/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs
index b8a20de4..f0cb8695 100644
--- a/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs
+++ b/build/SharpGLTF.CodeGen/Ext.EXT_InstanceFeatures.cs
@@ -8,7 +8,7 @@ class ExtInstanceFeaturesExtension : SchemaProcessor
     {
         public override string GetTargetProject() { return Constants.CesiumProjectDirectory; }
 
-        private static string RootSchemaUri => Constants.CustomExtensionsPath("EXT_instance_features", "node.EXT_instance_features.schema.json");
+        private static string NodeSchemaUri => Constants.CustomExtensionsPath("EXT_instance_features", "node.EXT_instance_features.schema.json");
 
         public override void PrepareTypes(CSharpEmitter newEmitter, SchemaType.Context ctx)
         {
@@ -23,11 +23,11 @@ public override void PrepareTypes(CSharpEmitter newEmitter, SchemaType.Context c
 
         private static SchemaType.Context ProcessNode()
         {
-            var ctx = SchemaProcessing.LoadSchemaContext(RootSchemaUri);
+            var ctx = SchemaProcessing.LoadSchemaContext(NodeSchemaUri);
             ctx.IgnoredByCodeEmitter("glTF Property");
             ctx.IgnoredByCodeEmitter("glTF Child of Root Property");
             ctx.IgnoredByCodeEmitter("Texture Info");
             return ctx;
         }
     }
-}
\ No newline at end of file
+}

From 19c5f236dfee07eb6826c659f16c44094fea2fff Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Thu, 30 Nov 2023 09:48:50 +0100
Subject: [PATCH 13/14] .net 8 -> .net 6

---
 .github/workflows/dotnet.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/dotnet.yml b/.github/workflows/dotnet.yml
index d1425feb..bd76993b 100644
--- a/.github/workflows/dotnet.yml
+++ b/.github/workflows/dotnet.yml
@@ -8,7 +8,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        dotnet-version: [ '8.0.x' ]
+        dotnet-version: [ '6.0.x' ]
         os: [windows-latest, ubuntu-latest, macos-latest]
 
     steps:

From 448987a971db4e4cfe0070cc9bd610c61f3df317 Mon Sep 17 00:00:00 2001
From: Bert Temme <btemme@hotmail.com>
Date: Thu, 30 Nov 2023 09:58:13 +0100
Subject: [PATCH 14/14] fix the nunit tests

---
 tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
index e90b1b06..81ce995a 100644
--- a/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
+++ b/tests/SharpGLTF.Cesium.Tests/ExtInstanceFeaturesTests.cs
@@ -49,11 +49,10 @@ public void AddExtGpuInstanceFeatures()
 
             var cesiumExtInstanceFeaturesExtension = (MeshExtInstanceFeatures)model.LogicalNodes[0].Extensions.Where(item => item is MeshExtInstanceFeatures).FirstOrDefault();
 
-            Assert.NotNull(cesiumExtInstanceFeaturesExtension.FeatureIds);
-
-            Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds.Equals(featureIds));
-            Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds[0].Equals(featureId0));
-            Assert.IsTrue(cesiumExtInstanceFeaturesExtension.FeatureIds[1].Equals(featureId1));
+            Assert.That(cesiumExtInstanceFeaturesExtension.FeatureIds, Is.Not.Null);
+            Assert.That(cesiumExtInstanceFeaturesExtension.FeatureIds.Equals(featureIds));
+            Assert.That(cesiumExtInstanceFeaturesExtension.FeatureIds[0].Equals(featureId0));
+            Assert.That(cesiumExtInstanceFeaturesExtension.FeatureIds[1].Equals(featureId1));
 
             var ctx = new ValidationResult(model, ValidationMode.Strict, true);
             model.ValidateContent(ctx.GetContext());