start switching to export plugin callbacks

Editor/Scripts/GLTFExportMenu.cs

@@ -108,7 +108,7 @@ private static void ExportSceneGLB()
 		private static void Export(Transform[] transforms, bool binary, string sceneName)
 		{
 			var settings = GLTFSettings.GetOrCreateSettings();
-			var exportOptions = new ExportOptions { TexturePathRetriever = RetrieveTexturePath };
+			var exportOptions = new ExportContext { TexturePathRetriever = RetrieveTexturePath };
 			var exporter = new GLTFSceneExporter(transforms, exportOptions);
 
 			var invokedByShortcut = Event.current?.type == EventType.KeyDown;

Editor/Scripts/GLTFImporter.cs

@@ -46,7 +46,7 @@ namespace UnityGLTF
 #else
 	[ScriptedImporter(ImporterVersion, new[] { "glb" })]
 #endif
-    public class GLTFImporter : ScriptedImporter, IGLTFImportRemap
+    public class GLTFImporter : ScriptedImporter
     {
 	    private const int ImporterVersion = 9;
 
@@ -236,7 +236,7 @@ public override void OnImportAsset(AssetImportContext ctx)
 		        if (plugin != null && plugin.Enabled)
 		        {
 			        var instance = plugin.CreateInstance(context);
-			        if(instance != null) plugins.Add(instance);
+			        if (instance != null) plugins.Add(instance);
 		        }
 	        }
 

Editor/Scripts/Plugins/GltfPluginEditor.cs

@@ -0,0 +1,21 @@
+using UnityEditor;
+using UnityGLTF.Plugins;
+
+namespace UnityGLTF
+{
+    [CustomEditor(typeof(GltfPlugin), true)]
+    public class GltfPluginEditor: Editor
+    {
+        // Follows the default implementation of OnInspectorGUI, but skips the script field
+        public override void OnInspectorGUI()
+        {
+            serializedObject.Update();
+            var iterator = serializedObject.GetIterator();
+            // skip script field
+            iterator.NextVisible(true);
+            while (iterator.NextVisible(false))
+                EditorGUILayout.PropertyField(iterator, true);
+            serializedObject.ApplyModifiedProperties();
+        }
+    }
+}

Editor/Scripts/ShaderGraph/MaterialEditorBridge.cs

@@ -23,7 +23,7 @@ private static void OnImmutableMaterialChanged(Material material)
 			// var mainAsset = AssetDatabase.LoadMainAssetAtPath(assetPath);
 
 			// Transform[] rootTransforms = null;
-			var exporter = new GLTFSceneExporter((Transform[]) null, new ExportOptions());
+			var exporter = new GLTFSceneExporter((Transform[]) null, new ExportContext());
 			// load all materials from mainAsset
 			var importer = AssetImporter.GetAtPath(assetPath) as GLTFImporter;
 			if (!importer) return;

Runtime/Scripts/Extensions/MaterialExtensions.cs

@@ -2,23 +2,57 @@
 using GLTF.Schema;
 using UnityEngine;
 using UnityGLTF.Extensions;
+using UnityGLTF.Plugins;
 #if UNITY_EDITOR
 using UnityEditor;
 #endif
 
 namespace UnityGLTF
 {
-	public static class MaterialExtensions
+	// When a plugin is registered with the default settings (the scriptable object in the project),
+	// it will be active "by default" when someone uses those default settings.
+	// e.g. it's used when someone uses the built-in editor methods for exporting objects.
+	// When using the API, one needs to manually register wanted plugins and configure them
+	// (can get the default settings and modify them).
+
+	// Plugins can contain any number of extensions, but are encouraged to specify in the description
+	// which extensions are imported/exported with that plugin.
+	// Theoretically there could be multiple plugins operating on the same extension in different ways, in
+	// which case we currently can't warn about conflicts; they would all run.
+	// If plugins were required to list the extensions they operate on, we could warn about conflicts.
+
+	// Plugins are ScriptableObjects which are added to the default GLTFSettings scriptable object.
+	// Their public serialized fields are exposed in the inspector, and they can be enabled/disabled.
+	// Plugins replace both GLTFSceneExporter.* static callbacks and GLTFSceneExporter.ExportOptions callbacks
+	// to allow for more control.
+
+	// Example cases where separate plugins operate on the same data:
+	// - exporting UI as custom extension vs. baking UI to mesh
+	// - exporting Audio in a custom extension vs. using KHR_audio
+	// - exporting LODs as custom extension vs. using MSFT_lod
+	// - exporting particle systems as custom extension vs. baking to mesh
+
+	// Plugins can either be added manually to ExportOptions.plugins / ImportContext.plugins
+	// or advertise themselves via a static callback which allows configuring their settings in the inspector.
+	// For each new instance of GLTFSceneExporter, new instances of plugins are created.
+	// For each new instance of GLTFSceneImporter, new instances of plugins are created.
+
+	public class MaterialExtensionsPlugin: GltfExportPlugin
 	{
-#if UNITY_EDITOR
-		[InitializeOnLoadMethod]
-#endif
-		[RuntimeInitializeOnLoadMethod]
-		static void InitExt()
+		public bool KHR_materials_ior = true;
+		public bool KHR_materials_transmission = true;
+		public bool KHR_materials_volume = true;
+
+		public override GltfExportPluginContext CreateInstance(ExportContext context)
 		{
-			GLTFSceneExporter.AfterMaterialExport += GLTFSceneExporterOnAfterMaterialExport;
+			return new MaterialExtensions();
 		}
 
+		public override string DisplayName => "Material Extensions";
+	}
+
+	public class MaterialExtensions: GltfExportPluginContext
+	{
 		private static readonly int thicknessTexture = Shader.PropertyToID("thicknessTexture");
 		private static readonly int thicknessFactor = Shader.PropertyToID("thicknessFactor");
 		private static readonly int attenuationDistance = Shader.PropertyToID("attenuationDistance");
@@ -45,8 +79,7 @@ static void InitExt()
 		private static readonly int clearcoatRoughnessTexture = Shader.PropertyToID("clearcoatRoughnessTexture");
 		private static readonly int clearcoatNormalTexture = Shader.PropertyToID("clearcoatNormalTexture");
 
-
-		private static void GLTFSceneExporterOnAfterMaterialExport(GLTFSceneExporter exporter, GLTFRoot gltfroot, Material material, GLTFMaterial materialnode)
+		public override void AfterMaterialExport(GLTFSceneExporter exporter, GLTFRoot gltfroot, Material material, GLTFMaterial materialnode)
 		{
 			if (!material) return;
 
@@ -193,8 +226,6 @@ private static void GLTFSceneExporterOnAfterMaterialExport(GLTFSceneExporter exp
 					cc.clearcoatRoughnessTexture = exporter.ExportTextureInfoWithTextureTransform(material, material.GetTexture(clearcoatRoughnessTexture), nameof(clearcoatRoughnessTexture));
 				if (material.HasProperty(clearcoatNormalTexture))
 					cc.clearcoatNormalTexture = exporter.ExportTextureInfoWithTextureTransform(material, material.GetTexture(clearcoatNormalTexture), nameof(clearcoatNormalTexture));
-
-
 			}
 		}
 	}