don't require SwapChain to be passed to viewer.render - this will just render into all registered swapchains

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

@@ -203,8 +203,8 @@ abstract class FilamentApp<T> {
   ///
   ///
   ///
-  Future setMaterialInstanceAt(
+  Future setMaterialInstanceAt(ThermionEntity entity, int primitiveIndex,
-      ThermionEntity entity, int primitiveIndex, MaterialInstance materialInstance);
+      MaterialInstance materialInstance);
 
   ///
   ///
@@ -216,6 +216,11 @@ abstract class FilamentApp<T> {
   ///
   Future unregister(covariant SwapChain swapChain, covariant View view);
 
+  ///
+  ///
+  ///
+  Future<Iterable<SwapChain>> getSwapChains();
+
   ///
   ///
   ///

thermion_dart/lib/src/viewer/src/ffi/src/thermion_viewer_ffi.dart

@@ -123,11 +123,14 @@ class ThermionViewerFFI extends ThermionViewer {
   ///
   ///
   @override
-  Future render(SwapChain swapchain) async {
+  Future render() async {
+    final swapChains =
+        await (FilamentApp.instance as FFIFilamentApp).getSwapChains();
+    for (final swapChain in swapChains) {
       await withBoolCallback(
         (cb) => Renderer_beginFrameRenderThread(
           app.renderer,
-        (swapchain as FFISwapChain).swapChain,
+          swapChain.getNativeHandle(),
           0.toBigInt,
           cb,
         ),
@@ -143,6 +146,7 @@ class ThermionViewerFFI extends ThermionViewer {
       );
       await FilamentApp.instance!.flush();
     }
+  }
 
   double _msPerFrame = 1000.0 / 60.0;
 

thermion_dart/lib/src/viewer/src/thermion_viewer_base.dart

@@ -39,9 +39,9 @@ abstract class ThermionViewer {
   Future setRendering(bool render);
 
   ///
-  /// Render a single frame immediately.
+  /// Render a single frame immediately into all registered swapchains.
   ///
-  Future render(SwapChain swapChain);
+  Future render();
 
   ///
   ///

thermion_dart/test/render_thread_tests.dart

@@ -13,20 +13,11 @@ void main() async {
   test("request frame on render thread", () async {
     await testHelper.withViewer((viewer) async {
       await viewer.render();
-
+      await Future.delayed(Duration(seconds: 1));
-      await Future.delayed(Duration(milliseconds: 1));
-
-      // var data = viewer.metalTexture.getTextureBytes()!;
-      // var pixels = data.bytes.cast<Uint8>().asTypedList(data.length);
-
-      // savePixelBufferToBmp(
-      //     pixels, 500, 500, "${testHelper.testDir}/request_frame.bmp");
-
       await viewer.setRendering(true);
-
       await Future.delayed(Duration(seconds: 1));
       await FilamentApp.instance!.requestFrame();
       await testHelper.capture(viewer.view, "render_thread_2");
-    });
+    }, addSkybox: true);
   });
 }