Fixed issue setting node and mesh morph weights.

src/SharpGLTF.Core/Schema2/_Extensions.MorphWeights.cs

@@ -24,8 +24,8 @@ namespace SharpGLTF.Schema2
                     list[i] = 0;
                 }
 
-                foreach (var (index, weight) in weights.GetIndexedWeights())
-                {
+                foreach (var (index, weight) in weights.GetNonZeroWeights())
+                {                    
                     list[index] = weight;
                 }
             }

src/SharpGLTF.Core/Transforms/SparseWeight8.cs

@@ -539,6 +539,18 @@ namespace SharpGLTF.Transforms
             yield return (Index7, Weight7);
         }
 
+        public IEnumerable<(int Index, float Weight)> GetNonZeroWeights()
+        {
+            if (Weight0 != 0) yield return (Index0, Weight0);
+            if (Weight1 != 0) yield return (Index1, Weight1);
+            if (Weight2 != 0) yield return (Index2, Weight2);
+            if (Weight3 != 0) yield return (Index3, Weight3);
+            if (Weight4 != 0) yield return (Index4, Weight4);
+            if (Weight5 != 0) yield return (Index5, Weight5);
+            if (Weight6 != 0) yield return (Index6, Weight6);
+            if (Weight7 != 0) yield return (Index7, Weight7);
+        }
+
         public static SparseWeight8 Blend(ReadOnlySpan<SparseWeight8> sparses, ReadOnlySpan<float> weight)
         {
             var r = default(SparseWeight8);
@@ -673,17 +685,7 @@ namespace SharpGLTF.Transforms
             return new SparseWeight8(rrr);
         }
 
-        internal IEnumerable<(int Index, float Weight)> GetNonZeroWeights()
-        {
-            if (Weight0 != 0) yield return (Index0, Weight0);
-            if (Weight1 != 0) yield return (Index1, Weight1);
-            if (Weight2 != 0) yield return (Index2, Weight2);
-            if (Weight3 != 0) yield return (Index3, Weight3);
-            if (Weight4 != 0) yield return (Index4, Weight4);
-            if (Weight5 != 0) yield return (Index5, Weight5);
-            if (Weight6 != 0) yield return (Index6, Weight6);
-            if (Weight7 != 0) yield return (Index7, Weight7);
-        }
+        
 
         private float GetExpandedAt(int idx)
         {

tests/SharpGLTF.Core.Tests/Schema2/Authoring/AdvancedCreationTests.cs

@@ -11,8 +11,79 @@ namespace SharpGLTF.Schema2.Authoring
 {
     internal class AdvancedCreationTests
     {
+        [Test(Description = "Creates a primary mesh, and then another mesh derived from the data of the first mesh")]
+        public void CreateDerivedSparseMeshes()
+        {
+            TestContext.CurrentContext.AttachGltfValidatorLinks();
+
+            // create model
+            var model = ModelRoot.CreateModel();
+
+            // create scene
+            var scene = model.DefaultScene = model.UseScene("Default");            
+
+            // create material
+            var material = model
+                .CreateMaterial("Default")
+                .WithDefault(new Vector4(0, 1, 0, 1));
+
+            // create primary node
+            var rnode = scene.CreateNode("Triangle Node");
+
+            // create primary mesh
+            var rmesh = rnode.Mesh = model.CreateMesh("Triangle Mesh");
+
+            // create the vertex positions
+            var positions = new[]
+            {
+                new Vector3(0, 10, 0),
+                new Vector3(-10, -10, 0),
+                new Vector3(10, -10, 0),
+            };
+
+            // create an index buffer and fill it            
+            var indices = new[] { 0, 1, 2 };
+
+            // create primary mesh primitive
+            var originalPrimitive = rmesh
+                .CreatePrimitive().WithMaterial(material)
+                .WithVertexAccessor("POSITION", positions, true) // notice the (true) to explicitly set ByteStride, which is required for shared BufferViews
+                .WithIndicesAccessor(PrimitiveType.TRIANGLES, indices);
+            
+
+            // create derived node
+            rnode = scene.CreateNode("derived Triangle Node");
+            rnode.LocalTransform = new Transforms.AffineTransform(Quaternion.Identity, new Vector3(30, 0, 0));
+
+            // create a sparse accessor based on the primary mesh position accessor, and a sparse override.
+
+            var positionsOverride = new Dictionary<int, Vector3>();
+            positionsOverride[0] = new Vector3(0, 30, 0);
+
+            var sparseAccessor = model.CreateAccessor();
+            sparseAccessor.SetDataFrom(originalPrimitive.GetVertexAccessor("POSITION")); // set base positions from original primitive
+            sparseAccessor.CreateSparseData(positionsOverride);
+
+            // create derived mesh
+            var dmesh = rnode.Mesh = model.CreateMesh("derived Triangle Mesh");
+
+            var derivedPrimitive = dmesh.CreatePrimitive().WithMaterial(material);
+            derivedPrimitive.SetVertexAccessor("POSITION", sparseAccessor);
+            derivedPrimitive.SetIndexAccessor(originalPrimitive.IndexAccessor);
+
+            // save model
+
+            model.AttachToCurrentTest("result.glb");
+            model.AttachToCurrentTest("result.gltf");
+
+            var m1array = sparseAccessor.AsVector3Array();
+            Assert.That(m1array[0], Is.EqualTo(positionsOverride[0]));
+            Assert.That(m1array[1], Is.EqualTo(positions[1]));
+            Assert.That(m1array[2], Is.EqualTo(positions[2]));
+        }
+
         [Test(Description = "Creates a model with a triangle mesh")]
-        public void CreateSceneWithSparseAccessors()
+        public void CreateMorphTargetsWithSparseAccessors()
         {
             TestContext.CurrentContext.AttachGltfValidatorLinks();
 
@@ -47,41 +118,27 @@ namespace SharpGLTF.Schema2.Authoring
             // create mesh primitive
             var primitive = rmesh
                 .CreatePrimitive()
-                .WithVertexAccessor("POSITION", positions, true) // (true) notice here that we request creating a BufferView with explicit ByteStride
+                .WithVertexAccessor("POSITION", positions)
                 .WithIndicesAccessor(PrimitiveType.TRIANGLES, indices)
                 .WithMaterial(material);
 
             // create morph target 0
-            
-            var morphs0Pos = new Dictionary<int, Vector3>(); // <VertexIndex, Position>
-            morphs0Pos[2] = new Vector3(15, -15, 0);
-
-            var morphs0Acc = model.CreateAccessor();
-            morphs0Acc.SetDataFrom(primitive.GetVertexAccessor("POSITION")); // set base data from position attribute accessor
-            morphs0Acc.CreateSparseData(morphs0Pos);
 
-            var morphs0 = new Dictionary<string, Accessor>();
-            morphs0["POSITION"] = morphs0Acc;
-
-            primitive.SetMorphTargetAccessors(0, morphs0);
+            var morphs0Pos = new Dictionary<int, Vector3>(); // <VertexIndex, PositionDelta>
+            morphs0Pos[2] = new Vector3(5, -5, 0);
+            var morphs0Acc = _SetMorphTarget(primitive, 0, morphs0Pos);
 
             // create morph target 1
 
-            var morphs1Pos = new Dictionary<int, Vector3>(); // <VertexIndex, Position>
-            morphs1Pos[0] = new Vector3(0, 15, 0);
-
-            var morphs1Acc = model.CreateAccessor();
-            morphs1Acc.SetDataFrom(primitive.GetVertexAccessor("POSITION")); // set base data from position attribute accessor
-            morphs1Acc.CreateSparseData(morphs1Pos);
-
-            var morphs1 = new Dictionary<string, Accessor>();
-            morphs1["POSITION"] = morphs1Acc;
-
-            primitive.SetMorphTargetAccessors(1, morphs1);
+            var morphs1Pos = new Dictionary<int, Vector3>(); // <VertexIndex, PositionDelta>
+            morphs1Pos[0] = new Vector3(0, 10, 0);
+            var morphs1Acc = _SetMorphTarget(primitive, 1, morphs1Pos);
 
             // initialize node with a specific weights blend
+            
+            rnode.SetMorphWeights(Transforms.SparseWeight8.Create((0, 0.95f), (1, 0.75f))); // morph 0 at 0.95, morph 1 at 0.75
 
-            rnode.SetMorphWeights(Transforms.SparseWeight8.Create(  (0, 0.95f), (1, 0.75f) )); // morph 0 at 0.95, morph 1 at 0.75
+            Assert.That(rnode.MorphWeights, Is.EqualTo(new float[] { 0.95f, 0.75f }));
 
             // save model
 
@@ -91,15 +148,29 @@ namespace SharpGLTF.Schema2.Authoring
             // check accessors
 
             var m0array = morphs0Acc.AsVector3Array();
-            Assert.That(m0array[0], Is.EqualTo(positions[0]));
-            Assert.That(m0array[1], Is.EqualTo(positions[1]));
+            Assert.That(m0array[0], Is.EqualTo(Vector3.Zero));
+            Assert.That(m0array[1], Is.EqualTo(Vector3.Zero));
             Assert.That(m0array[2], Is.EqualTo(morphs0Pos[2]));
 
             var m1array = morphs1Acc.AsVector3Array();
             Assert.That(m1array[0], Is.EqualTo(morphs1Pos[0]));
-            Assert.That(m1array[1], Is.EqualTo(positions[1]));
-            Assert.That(m1array[2], Is.EqualTo(positions[2]));
+            Assert.That(m1array[1], Is.EqualTo(Vector3.Zero));
+            Assert.That(m1array[2], Is.EqualTo(Vector3.Zero));
+
+        }
+
+        private static Accessor _SetMorphTarget(MeshPrimitive primitive, int morphTargetIndex, Dictionary<int, Vector3> morphs1Pos)
+        {
+            var accessor = primitive.LogicalParent.LogicalParent.CreateAccessor();
+            accessor.SetZeros(3, DimensionType.VEC3, EncodingType.FLOAT, false);
+            accessor.CreateSparseData(morphs1Pos);
+
+            var attributes = new Dictionary<string, Accessor>();
+            attributes["POSITION"] = accessor;
+
+            primitive.SetMorphTargetAccessors(morphTargetIndex, attributes);
 
+            return accessor;
         }
     }
 }