Implement KHR_materials_transmission Gltf extension

src/ThreeDModels/Format/Gltf/Extensions/KHR_materials_transmission.cs

@@ -0,0 +1,91 @@
+using System.Text.Json;
+using ThreeDModels.Format.Gltf.Elements;
+using ThreeDModels.Format.Gltf.IO;
+using static ThreeDModels.Format.Gltf.IO.Utf8JsonReaderHelpers;
+
+namespace ThreeDModels.Format.Gltf.Extensions;
+
+/// <summary>
+/// Represents an object that defines the optical transmission of a material.
+/// </summary>
+public class KHR_materials_transmission : IGltfProperty
+{
+    /// <summary>
+    /// The base percentage of non-specularly reflected light that is transmitted through the surface.
+    /// </summary>
+    public float TransmissionFactor { get; set; }
+    /// <summary>
+    /// A texture that defines the transmission percentage of the surface, sampled from the R channel. These values are linear, and will be multiplied by transmissionFactor.
+    /// </summary>
+    public TextureInfo? TransmissionTexture { get; set; }
+    public Dictionary<string, object?>? Extensions { get; set; }
+    public object? Extras { get; set; }
+}
+
+public class KhrMaterialsTransmissionExtension : IGltfExtension
+{
+    public string Name => nameof(KHR_materials_transmission);
+    public const float Default_TransmissionFactor = 0.0f;
+
+    public object? Read(ref Utf8JsonReader jsonReader, GltfReaderContext context, Type parentType)
+    {
+        if (parentType != typeof(Material))
+        {
+            throw new InvalidDataException("KHR_materials_transmission must be used in a Material.");
+        }
+        float? transmissionFactor = null;
+        TextureInfo? transmissionTexture = null;
+        Dictionary<string, object?>? extensions = null;
+        object? extras = null;
+        if (jsonReader.TokenType == JsonTokenType.PropertyName && jsonReader.Read())
+        {
+        }
+        if (jsonReader.TokenType == JsonTokenType.Null)
+        {
+            return null;
+        }
+        else if (jsonReader.TokenType != JsonTokenType.StartObject)
+        {
+            throw new InvalidDataException("Failed to find start of property.");
+        }
+        while (jsonReader.Read())
+        {
+            if (jsonReader.TokenType == JsonTokenType.EndObject)
+            {
+                break;
+            }
+            var propertyName = jsonReader.GetString();
+            if (propertyName == nameof(transmissionFactor))
+            {
+                transmissionFactor = ReadFloat(ref jsonReader);
+            }
+            else if (propertyName == nameof(transmissionTexture))
+            {
+                transmissionTexture = TextureInfoSerialization.Read(ref jsonReader, context);
+            }
+            else if (propertyName == nameof(extensions))
+            {
+                extensions = ExtensionsSerialization.Read<KHR_materials_transmission>(ref jsonReader, context);
+            }
+            else if (propertyName == nameof(extras))
+            {
+                extras = JsonSerialization.Read(ref jsonReader, context);
+            }
+            else
+            {
+                throw new InvalidDataException($"Unknown property: {propertyName}");
+            }
+        }
+        if (transmissionFactor != null && (transmissionFactor < 0.0f || transmissionFactor > 1.0f))
+        {
+            throw new InvalidDataException("KHR_materials_transmission.transmissionFactor must be between 0.0 and 1.0.");
+        }
+        return new KHR_materials_transmission()
+        {
+            TransmissionFactor = transmissionFactor ?? Default_TransmissionFactor,
+            TransmissionTexture = transmissionTexture,
+            Extensions = extensions,
+            Extras = extras,
+        };
+    }
+}