Fixed MaterialBuilder's conversion to glTF not copying the IOR value.

Fixes #246

src/SharpGLTF.Toolkit/Schema2/MaterialExtensions.cs

@@ -390,7 +390,7 @@ public static void CopyTo(this MaterialBuilder srcMaterial, Material dstMaterial
  dstMaterial.Alpha = srcMaterial.AlphaMode.ToSchema2();
  dstMaterial.AlphaCutoff = srcMaterial.AlphaCutoff;
  dstMaterial.DoubleSided = srcMaterial.DoubleSided;
- dstMaterial.IndexOfRefraction = srcMaterial.IndexOfRefraction;
+
 
  var hasClearCoat
  = srcMaterial.GetChannel("ClearCoat") != null
@@ -442,6 +442,10 @@ var hasVolume
  defMaterial = srcMaterial.CompatibilityFallback;
  }
 
+ // IOR must be set after dst material initialization,
+ // otherwise it's erased since it's stored in an extension
+ dstMaterial.IndexOfRefraction = srcMaterial.IndexOfRefraction;
+
  if (defMaterial != null)
  {
  if (defMaterial.ShaderStyle != "PBRMetallicRoughness") throw new ArgumentException(nameof(srcMaterial.CompatibilityFallback.ShaderStyle));
@@ -452,6 +456,10 @@ var hasVolume
  defMaterial.CopyChannelsTo(dstMaterial, "SpecularColor", "SpecularFactor");
  defMaterial.CopyChannelsTo(dstMaterial, "VolumeThickness", "VolumeAttenuation");
  }
+
+ // final validation
+
+ System.Diagnostics.Debug.Assert(dstMaterial.IndexOfRefraction == srcMaterial.IndexOfRefraction, "set IOR after dst material initialization"); 
  }
 
  public static void CopyChannelsTo(this MaterialBuilder srcMaterial, Material dstMaterial, params string[] channelKeys)

tests/SharpGLTF.Toolkit.Tests/Materials/MaterialBuilderTests.cs

@@ -6,6 +6,7 @@
 
 using NUnit.Framework;
 
+using SharpGLTF.Scenes;
 using SharpGLTF.Schema2;
 using SharpGLTF.Validation;
 
@@ -23,8 +24,8 @@ public void TestMaterialEquality()
  // ... And we could use it for general equality checks, but then, since
  // MaterialBuilder is NOT inmutable, it can mean that two materials can be equal
  // at a given time, and non equal at another. Furthermore, it would imply having
- // a hash code that changes over time. As a consequence, it could be impossible
- // to use MaterialBuilder as a dictionary Key.
+ // a hash code that changes over time. As a consequence, using MaterialBuilder as
+ // a dictionary key is possible, but dangerous if not carefully handled.
 
  var srcMaterial = _CreateUnlitMaterial();
 
@@ -100,6 +101,18 @@ public void CreateSpecularGlossinessWithFallback()
  Assert.That(MaterialBuilder.AreEqualByContent(material, material.Clone()), Is.True);
  }
 
+ [Test]
+ public void CreateIORWithFallback()
+ {
+ // https://github.com/vpenades/SharpGLTF/issues/246
+
+ var material = new MaterialBuilder("MaterialWithIOR");
+ material.IndexOfRefraction = 7;
+
+ Assert.That(MaterialBuilder.AreEqualByContent(material, material.Clone()), Is.True);
+ Assert.That(MaterialBuilder.AreEqualByContent(material, _Schema2Roundtrip(material)), Is.True); 
+ }
+
  private static MaterialBuilder _CreateUnlitMaterial()
  {
  var tex1 = ResourceInfo.From("shannon.png").FilePath;
@@ -192,7 +205,7 @@ private static MaterialBuilder _CreateClearCoatMaterial()
  .WithClearCoatRoughness(tex1, 1);
 
  return material;
- }
+ } 
 
  [Obsolete("SpecularGlossiness has been deprecated by Khronos")]
  private static MaterialBuilder _CreateSpecularGlossinessMaterialWithFallback()