add generic parameter to NativeHandle, rather than getNativeHandle()

thermion_dart/lib/src/filament/src/implementation/ffi_material.dart

@@ -200,8 +200,8 @@ class FFIMaterialInstance extends MaterialInstance<Pointer<TMaterialInstance>> {
   }
 
   @override
-  T getNativeHandle<T>() {
-    return pointer as T;
+  Pointer<TMaterialInstance> getNativeHandle() {
+    return pointer;
   }
 }
 

thermion_dart/lib/src/filament/src/implementation/ffi_scene.dart

@@ -6,13 +6,17 @@ import 'package:thermion_dart/src/filament/src/interface/skybox.dart';
 import 'package:thermion_dart/thermion_dart.dart';
 import 'package:logging/logging.dart';
 
-class FFIScene extends Scene {
+class FFIScene extends Scene<Pointer<TScene>> {
   late final _logger = Logger(this.runtimeType.toString());
 
   final Pointer<TScene> scene;
 
   FFIScene(this.scene);
 
+  Pointer<TScene> getNativeHandle() {
+    return scene;
+  }
+
   @override
   Future add(ThermionAsset asset) async {
     SceneAsset_addToScene(asset.getHandle(), scene);

thermion_dart/lib/src/filament/src/implementation/ffi_swapchain.dart

@@ -1,10 +1,10 @@
 import 'package:thermion_dart/thermion_dart.dart';
 
-class FFISwapChain extends SwapChain<Pointer> {
+class FFISwapChain extends SwapChain<Pointer<TSwapChain>> {
   
   final Pointer<TSwapChain> pointer;
 
-  T getNativeHandle<T>() => pointer as T;
+  Pointer<TSwapChain> getNativeHandle() => pointer;
 
   FFISwapChain(this.pointer);
   

thermion_dart/lib/src/filament/src/implementation/ffi_view.dart

@@ -150,8 +150,8 @@ class FFIView extends View {
     View_setRenderQuality(view, quality.index);
   }
 
-  Future setScene(covariant FFIScene scene) async {
-    View_setScene(view, scene.scene);
+  Future setScene(Scene scene) async {
+    View_setScene(view, scene.getNativeHandle());
   }
 
   @override

thermion_dart/lib/src/filament/src/interface/native_handle.dart

@@ -7,5 +7,5 @@
 /// not a compile-time error). 
 ///
 abstract class NativeHandle<T> {
-  T getNativeHandle<T>();
+  T getNativeHandle();
 }

thermion_dart/lib/src/filament/src/interface/scene.dart

@@ -1,7 +1,9 @@
+import 'package:thermion_dart/src/filament/src/interface/native_handle.dart';
 import 'package:thermion_dart/src/filament/src/interface/skybox.dart';
 import 'package:thermion_dart/thermion_dart.dart';
 
-abstract class Scene {
+abstract class Scene<T> extends NativeHandle<T> {
+  
   /// Adds all renderable entities in [asset] to this scene.
   ///
   ///