Optimized materials agregation.

src/SharpGLTF.Toolkit/Materials/MaterialBuilder.cs

@@ -71,7 +71,22 @@ namespace SharpGLTF.Materials
 
             if (!AreEqual(x._CompatibilityFallbackMaterial, y._CompatibilityFallbackMaterial)) return false;
 
-            return Enumerable.SequenceEqual(x._Channels, y._Channels, ChannelBuilder.ContentComparer);
+            // gather all unique channel keys used by both materials.
+
+            var channelKeys = x._Channels
+                .Concat(y._Channels)
+                .Select(item => item.Key)
+                .Distinct();
+
+            foreach (var ckey in channelKeys)
+            {
+                var xc = x.GetChannel(ckey);
+                var yc = y.GetChannel(ckey);
+
+                if (!ChannelBuilder.AreEqual(xc, yc)) return false;
+            }
+
+            return true;
         }
 
         public static int GetContentHashCode(MaterialBuilder x)

src/SharpGLTF.Toolkit/Scenes/SceneBuilder.Schema2.cs

@@ -4,16 +4,18 @@ using System.Linq;
 using System.Text;
 using System.Numerics;
 
+using SharpGLTF.Schema2;
+
 namespace SharpGLTF.Scenes
 {
-    using Schema2;
-
     using MESHBUILDER = Geometry.IMeshBuilder<Materials.MaterialBuilder>;
 
     class Schema2SceneBuilder
     {
         #region data
 
+        private readonly Dictionary<Materials.MaterialBuilder, Material> _Materials = new Dictionary<Materials.MaterialBuilder, Material>();
+
         private readonly Dictionary<MESHBUILDER, Mesh> _Meshes = new Dictionary<MESHBUILDER, Mesh>();
 
         private readonly Dictionary<NodeBuilder, Node> _Nodes = new Dictionary<NodeBuilder, Node>();
@@ -28,15 +30,38 @@ namespace SharpGLTF.Scenes
 
         public void AddScene(Scene dstScene, SceneBuilder srcScene)
         {
-            // gather all MeshBuilder unique instances
-            // and group them by their vertex attribute layout.
+            // gather all MaterialBuilder unique instances
+            // find and group materials that have the same content.
 
-            var meshGroups = srcScene.Instances
+            var materialGroups = srcScene.Instances
                 .Select(item => item.GetGeometryAsset())
                 .Where(item => item != null)
+                .SelectMany(item => item.Primitives)
+                .Select(item => item.Material)
+                .Where(item => item != null)
                 .Distinct()
                 .ToList()
-                .GroupBy(item => item.GetType());
+                .GroupBy(item => item, Materials.MaterialBuilder.ContentComparer);
+
+            foreach (var mg in materialGroups)
+            {
+                var val = dstScene.LogicalParent.CreateMaterial(mg.Key);
+
+                foreach (var key in mg)
+                {
+                    _Materials[key] = val;
+                }
+            }
+
+            // gather all MeshBuilder unique instances
+            // and group them by their vertex attribute layout.
+
+            var meshGroups = srcScene.Instances
+            .Select(item => item.GetGeometryAsset())
+            .Where(item => item != null)
+            .Distinct()
+            .ToList()
+            .GroupBy(item => item.GetType());
 
             // create Schema2.Mesh collections for every gathered group.
 
@@ -44,7 +69,7 @@ namespace SharpGLTF.Scenes
             {
                 var meshArray = meshGroup.ToArray();
 
-                var meshDst = dstScene.LogicalParent.CreateMeshes(meshArray);
+                var meshDst = dstScene.LogicalParent.CreateMeshes(mat => _Materials[mat], meshArray);
 
                 for (int i = 0; i < meshArray.Length; ++i)
                 {
@@ -108,6 +133,10 @@ namespace SharpGLTF.Scenes
 
     public partial class SceneBuilder
     {
+        /// <summary>
+        /// Converts this <see cref="SceneBuilder"/> instance into a <see cref="ModelRoot"/> instance.
+        /// </summary>
+        /// <returns>A new <see cref="ModelRoot"/> instance.</returns>
         public ModelRoot ToSchema2()
         {
             var dstModel = ModelRoot.CreateModel();