add reading unit test for EXT_Mesh_Features

src/SharpGLTF.Ext.3DTiles/Schema2/Ext.FeatureID.cs

@@ -231,6 +231,8 @@ namespace SharpGLTF.Schema2.Tiles3D
             return LogicalParent?.LogicalParent?.LogicalParent?.LogicalParent?.LogicalParent;
         }
 
+        public IReadOnlyList<int> GetChannels() => _channels;
+
         public void SetChannels(IReadOnlyList<int> channels)
         {
             Guard.NotNullOrEmpty(channels, nameof(channels));

src/SharpGLTF.Ext.3DTiles/Schema2/Ext.Features.cs

@@ -267,7 +267,9 @@ namespace SharpGLTF.Schema2
                     if (featureId.Attribute.HasValue)
                     {
                         var expectedVertexAttribute = $"_FEATURE_ID_{featureId.Attribute}";
-                        Guard.NotNull(_meshPrimitive.GetVertexAccessor(expectedVertexAttribute), expectedVertexAttribute, $"The primitive should have custom vertex attribute {expectedVertexAttribute}.");
+                        var featureIdVertex = _meshPrimitive.GetVertexAccessor(expectedVertexAttribute);
+                        Guard.NotNull(featureIdVertex, expectedVertexAttribute, $"The primitive should have custom vertex attribute {expectedVertexAttribute}.");
+                        Guard.IsTrue(!featureIdVertex.Normalized, expectedVertexAttribute, $"The custom vertex attribute {expectedVertexAttribute} should not be normalized.");
                     }
 
                     featureId.ValidateFeatureIdReferences(_meshPrimitive.LogicalParent.LogicalParent);
@@ -281,6 +283,28 @@ namespace SharpGLTF.Schema2
 
                         var modelRoot = _meshPrimitive.LogicalParent.LogicalParent;
                         validate.IsNullOrIndex(nameof(texture), texture.TextureCoordinate, modelRoot.LogicalTextures);
+
+                        var samplers = modelRoot.LogicalTextureSamplers;
+                        foreach(var sampler in samplers)
+                        {
+                            Guard.IsTrue(sampler.MagFilter == TextureInterpolationFilter.NEAREST, $"Texture magnification filter must be 9728 (NEAREST) but is set to {sampler.MagFilter}");
+                            Guard.IsTrue(sampler.MinFilter == TextureMipMapFilter.NEAREST, $"Texture minification filtering must be 9728 (NEAREST) but is set to {sampler.MinFilter}");
+                        }
+
+                        // check on channels as workaround
+                        // better solution: read the channels of the used texture
+                        // var logicalTexture = modelRoot.LogicalTextures[texture.TextureCoordinate];
+                        // var image = logicalTexture.PrimaryImage;
+                        var channels = texture.GetChannels();
+
+                        // chack that the length of channels list is maximum 4
+                        Guard.IsTrue(channels.Count <= 4, $"The number of channels must be maximum 4 but is {channels.Count}");
+
+                        // check that value in channels is minimum 0 and maximum 3
+                        foreach (var channel in channels)
+                        {
+                            Guard.IsTrue(channel >= 0 && channel <= 3, $"Channel value must be between 0 and 3 but has channel {channel}");
+                        }
                     }
                 }
 
@@ -297,6 +321,32 @@ namespace SharpGLTF.Schema2
                 foreach (var featureId in _featureIds)
                 {
                     featureId.ValidateFeatureIdContent();
+
+                    if (featureId.Attribute != null)
+                    {
+                        var expectedVertexAttribute = $"_FEATURE_ID_{featureId.Attribute}";
+                        var vertex = _meshPrimitive.GetVertexAccessor(expectedVertexAttribute);
+                        var distinctFeatureIds = vertex.AsScalarArray().Distinct().ToList();
+
+                        if (featureId.NullFeatureId.HasValue)
+                        {
+                            distinctFeatureIds.Remove(featureId.NullFeatureId.Value);
+                        }
+
+                        var count = distinctFeatureIds.Count();
+                        Guard.IsTrue(featureId.FeatureCount == count, $"Mismatch between FeatureCount ({featureId.FeatureCount}) and Feature Attribute ({count})");
+                    }
+                    var texture = featureId.GetTexture();
+                    if (texture != null)
+                    {
+                        var expectedTexCoordAttribute = $"TEXCOORD_{texture.TextureCoordinate}";
+                        var vertex = _meshPrimitive.GetVertexAccessor(expectedTexCoordAttribute);
+                        var distinctFeatureIds = vertex.AsVector2Array().Count();
+
+                        Guard.IsTrue(featureId.FeatureCount == distinctFeatureIds, $"Mismatch between FeatureCount ({featureId.FeatureCount}) and Feature Texture ({distinctFeatureIds})");
+                    }
+
+
                 }
 
                 base.OnValidateContent(validate);
@@ -305,5 +355,5 @@ namespace SharpGLTF.Schema2
             #endregion
         }
 
-    }    
+    }
 }

tests/SharpGLTF.Cesium.Tests/ExtMeshFeaturesTests.cs

@@ -6,6 +6,7 @@ using SharpGLTF.Scenes;
 using SharpGLTF.Validation;
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Numerics;
 
@@ -22,6 +23,37 @@ namespace SharpGLTF.Schema2.Tiles3D
             Tiles3DExtensions.RegisterExtensions();
         }
 
+        [Test(Description = "Reads glTF's with Cesium EXT_Mesh_Features")]
+        public void ReadExtMeshFeatures()
+        {
+            var gltffiles = Directory.GetFiles("./testfixtures/meshFeatures", "*.gltf", SearchOption.AllDirectories);
+            var glbfiles = Directory.GetFiles("./testfixtures/meshFeatures", "*.glb", SearchOption.AllDirectories);
+            var testfiles = gltffiles.Concat(glbfiles);
+
+            foreach (var file in testfiles)
+            {
+                var fileName = Path.GetFileName(file);
+
+                if (fileName.StartsWith("FeatureId")) 
+                {
+                    // we can expect an error loading this file
+                    Assert.That(() => ModelRoot.Load(file), Throws.Exception);
+                }
+                else
+                {
+                    var model = ModelRoot.Load(file);
+                    var cesiumExtMeshFeaturesExtension = model.LogicalMeshes[0].Primitives[0].GetExtension<MeshExtMeshFeatures>();
+                    if(cesiumExtMeshFeaturesExtension != null)
+                    {
+                        Assert.That(cesiumExtMeshFeaturesExtension.FeatureIds, Is.Not.Null);
+                        Assert.That(cesiumExtMeshFeaturesExtension.FeatureIds, Has.Count.GreaterThanOrEqualTo(1));
+                        var ctx = new ValidationResult(model, ValidationMode.Strict, true);
+                        model.ValidateContent(ctx.GetContext());
+                    }
+                }
+            }
+        }
+
         [Test(Description = "Test for settting the FeatureIds with vertex attributes. See sample https://github.com/CesiumGS/3d-tiles-samples/blob/main/glTF/EXT_mesh_features/FeatureIdAttribute")]
         // In the sample html code, there is a shader that uses the feature ID to color the triangle
         public void FeaturesIdAttributeTest()

tests/SharpGLTF.Cesium.Tests/ExtStructuralMetadataTests.cs

@@ -193,7 +193,7 @@ namespace SharpGLTF.Schema2.Tiles3D
 
             // Set the FeatureIds
             var cnt = propertyTable.Count;
-            var featureIdAttribute = new FeatureIDBuilder(1, 0, propertyTable);
+            var featureIdAttribute = new FeatureIDBuilder(2, 0, propertyTable);
             model.LogicalMeshes[0].Primitives[0].AddMeshFeatureIds(featureIdAttribute);
 
             // create files

tests/SharpGLTF.Cesium.Tests/SharpGLTF.Cesium.Tests.csproj

@@ -27,6 +27,17 @@
   </ItemGroup>
 
   <ItemGroup>
+	<Folder Include="testfixtures\meshFeatures\" />
+	<Folder Include="testfixtures\instanceFeatures\" />
+    <Folder Include="testfixtures\structuralMetadata\" />
+	<None Update="testfixtures\meshFeatures\**\*" CopyToOutputDirectory="PreserveNewest" />
+
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="testfixtures\meshFeatures\ValidFeatureIdAttributeWithLargerFeatureCount.gltf">
+      <CopyToOutputDirectory>Never</CopyToOutputDirectory>
+    </None>
     <None Update="tree.glb">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>

tests/SharpGLTF.Cesium.Tests/testfixtures/README.md

@@ -0,0 +1 @@
+3D Tiles Test fixtures are obtained from https://github.com/CesiumGS/3d-tiles-validator/tree/main/specs/data/gltfExtensions

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeAccessorNormalized.gltf

@@ -0,0 +1,103 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ],
+    "normalized": true
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
+    "buffer" : 0,
+    "byteOffset" : 0,
+    "byteLength" : 48,
+    "target" : 34963
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 48,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 240,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "featureCount" : 4,
+            "attribute" : 0
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeAccessorNotScalar.gltf

@@ -0,0 +1,102 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
+    "buffer" : 0,
+    "byteOffset" : 0,
+    "byteLength" : 48,
+    "target" : 34963
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 48,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 240,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "featureCount" : 4,
+            "attribute" : 0
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 2
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeAttributeInvalidType.gltf

@@ -0,0 +1,102 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
+    "buffer" : 0,
+    "byteOffset" : 0,
+    "byteLength" : 48,
+    "target" : 34963
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 48,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 240,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "featureCount" : 4,
+            "attribute" : "NOT_A_NUMBER"
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeAttributeInvalidValue.gltf

@@ -0,0 +1,102 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
+    "buffer" : 0,
+    "byteOffset" : 0,
+    "byteLength" : 48,
+    "target" : 34963
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 48,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 240,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "featureCount" : 4,
+            "attribute" : 12345
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeFeatureCountInvalidType.gltf

@@ -0,0 +1,102 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
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tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeFeatureCountInvalidValue.gltf

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tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeFeatureCountMismatch.gltf

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tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeFeatureCountMismatchForNullFeatureId.gltf

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tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeFeatureCountMissing.gltf

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tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeLabelInvalidType.gltf

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+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeLabelInvalidValue.gltf

@@ -0,0 +1,103 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
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+    "byteOffset" : 0,
+    "componentType" : 5123,
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+    "type" : "SCALAR",
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+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
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+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
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+  } ],
+  "bufferViews" : [ {
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+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "label": "NOT:A:VALID/IDENTIFIER",
+            "featureCount" : 4,
+            "attribute" : 0
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeNullFeatureIdInvalidType.gltf

@@ -0,0 +1,103 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
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+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
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+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "nullFeatureId": "NOT_A_NUMBER",
+            "featureCount" : 4,
+            "attribute" : 0
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/FeatureIdAttributeNullFeatureIdInvalidValue.gltf

@@ -0,0 +1,103 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
+    "buffer" : 0,
+    "byteOffset" : 0,
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+    "target" : 34963
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+    "byteOffset" : 48,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 240,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "nullFeatureId": -12345,
+            "featureCount" : 4,
+            "attribute" : 0
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/README.md

@@ -0,0 +1,19 @@
+
+
+The files in this directory are used for the specs for the `EXT_mesh_features`
+validation.
+
+The valid files have been taken from
+https://github.com/CesiumGS/3d-tiles-samples/tree/a256d9f68df15bbfc75ea3891f52c72a36d04202/glTF/EXT_mesh_features
+
+The `ValidFeatureIdTexture.glb` and `ValidFeatureIdAttributeDefault/` are 
+intended for basic tests of binary- and default (non-embedded) glTF assets. 
+
+The `ValidFeatureIdAttributeWithByteStride.glb` was created from the original
+`ValidFeatureIdTexture.gltf` by passing it through https://gltf.report/ , which 
+happens to write all attributes in an interleaved way, causing a byte stride 
+to be inserted. 
+
+The other files (starting with `FeatureIdTexture*` or `FeatureIdAttribute*`)
+have been edited to cause validation errors (with the error indicated by 
+their file name, as far as reasonably possible). 

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/ValidFeatureIdAttribute.gltf

@@ -0,0 +1,102 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
+  "buffers" : [ {
+    "uri" : "data:application/gltf-buffer;base64,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",
+    "byteLength" : 496
+  } ],
+  "bufferViews" : [ {
+    "buffer" : 0,
+    "byteOffset" : 0,
+    "byteLength" : 48,
+    "target" : 34963
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 48,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 240,
+    "byteLength" : 192,
+    "target" : 34962
+  }, {
+    "buffer" : 0,
+    "byteOffset" : 432,
+    "byteLength" : 64,
+    "byteStride" : 4,
+    "target" : 34962
+  } ],
+  "materials" : [ {
+    "pbrMetallicRoughness" : {
+      "baseColorFactor" : [ 0.5, 1.0, 0.5, 1.0 ],
+      "metallicFactor" : 0.0,
+      "roughnessFactor" : 1.0
+    },
+    "alphaMode" : "OPAQUE",
+    "doubleSided" : true
+  } ],
+  "meshes" : [ {
+    "primitives" : [ {
+      "extensions" : {
+        "EXT_mesh_features" : {
+          "featureIds" : [ {
+            "featureCount" : 4,
+            "attribute" : 0
+          } ]
+        }
+      },
+      "attributes" : {
+        "POSITION" : 1,
+        "NORMAL" : 2,
+        "_FEATURE_ID_0" : 3
+      },
+      "indices" : 0,
+      "material" : 0,
+      "mode" : 4
+    } ]
+  } ],
+  "nodes" : [ {
+    "mesh" : 0
+  } ],
+  "scene" : 0,
+  "scenes" : [ {
+    "nodes" : [ 0 ]
+  } ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/ValidFeatureIdAttributeDefault/ValidFeatureIdAttributeDefault.gltf

@@ -0,0 +1,159 @@
+{
+  "extensionsUsed": [
+    "EXT_mesh_features"
+  ],
+  "accessors": [
+    {
+      "bufferView": 0,
+      "byteOffset": 0,
+      "componentType": 5123,
+      "count": 24,
+      "type": "SCALAR",
+      "max": [
+        15
+      ],
+      "min": [
+        0
+      ]
+    },
+    {
+      "bufferView": 1,
+      "byteOffset": 0,
+      "componentType": 5126,
+      "count": 16,
+      "type": "VEC3",
+      "max": [
+        1,
+        1,
+        0
+      ],
+      "min": [
+        0,
+        0,
+        0
+      ]
+    },
+    {
+      "bufferView": 2,
+      "byteOffset": 0,
+      "componentType": 5126,
+      "count": 16,
+      "type": "VEC3",
+      "max": [
+        0,
+        0,
+        1
+      ],
+      "min": [
+        0,
+        0,
+        1
+      ]
+    },
+    {
+      "bufferView": 3,
+      "byteOffset": 0,
+      "componentType": 5121,
+      "count": 16,
+      "type": "SCALAR",
+      "max": [
+        3
+      ],
+      "min": [
+        0
+      ]
+    }
+  ],
+  "asset": {
+    "generator": "JglTF from https://github.com/javagl/JglTF",
+    "version": "2.0"
+  },
+  "buffers": [
+    {
+      "uri": "ValidFeatureIdAttributeDefault_data.bin",
+      "byteLength": 496
+    }
+  ],
+  "bufferViews": [
+    {
+      "buffer": 0,
+      "byteOffset": 0,
+      "byteLength": 48,
+      "target": 34963
+    },
+    {
+      "buffer": 0,
+      "byteOffset": 48,
+      "byteLength": 192,
+      "target": 34962
+    },
+    {
+      "buffer": 0,
+      "byteOffset": 240,
+      "byteLength": 192,
+      "target": 34962
+    },
+    {
+      "buffer": 0,
+      "byteOffset": 432,
+      "byteLength": 64,
+      "byteStride": 4,
+      "target": 34962
+    }
+  ],
+  "materials": [
+    {
+      "pbrMetallicRoughness": {
+        "baseColorFactor": [
+          0.5,
+          1,
+          0.5,
+          1
+        ],
+        "metallicFactor": 0,
+        "roughnessFactor": 1
+      },
+      "alphaMode": "OPAQUE",
+      "doubleSided": true
+    }
+  ],
+  "meshes": [
+    {
+      "primitives": [
+        {
+          "extensions": {
+            "EXT_mesh_features": {
+              "featureIds": [
+                {
+                  "featureCount": 4,
+                  "attribute": 0
+                }
+              ]
+            }
+          },
+          "attributes": {
+            "POSITION": 1,
+            "NORMAL": 2,
+            "_FEATURE_ID_0": 3
+          },
+          "indices": 0,
+          "material": 0,
+          "mode": 4
+        }
+      ]
+    }
+  ],
+  "nodes": [
+    {
+      "mesh": 0
+    }
+  ],
+  "scene": 0,
+  "scenes": [
+    {
+      "nodes": [
+        0
+      ]
+    }
+  ]
+}

tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/ValidFeatureIdAttributeWithLargerFeatureCount.gltf

@@ -0,0 +1,102 @@
+{
+  "extensionsUsed" : [ "EXT_mesh_features" ],
+  "accessors" : [ {
+    "bufferView" : 0,
+    "byteOffset" : 0,
+    "componentType" : 5123,
+    "count" : 24,
+    "type" : "SCALAR",
+    "max" : [ 15 ],
+    "min" : [ 0 ]
+  }, {
+    "bufferView" : 1,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 1.0, 1.0, 0.0 ],
+    "min" : [ 0.0, 0.0, 0.0 ]
+  }, {
+    "bufferView" : 2,
+    "byteOffset" : 0,
+    "componentType" : 5126,
+    "count" : 16,
+    "type" : "VEC3",
+    "max" : [ 0.0, 0.0, 1.0 ],
+    "min" : [ 0.0, 0.0, 1.0 ]
+  }, {
+    "bufferView" : 3,
+    "byteOffset" : 0,
+    "componentType" : 5121,
+    "count" : 16,
+    "type" : "SCALAR",
+    "max" : [ 3 ],
+    "min" : [ 0 ]
+  } ],
+  "asset" : {
+    "generator" : "JglTF from https://github.com/javagl/JglTF",
+    "version" : "2.0"
+  },
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tests/SharpGLTF.Cesium.Tests/testfixtures/meshFeatures/ValidFeatureIdAttributeWithNullFeatureId.gltf

@@ -0,0 +1,103 @@
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