add Dart-side methods

thermion_dart/lib/src/viewer/src/shared_types/camera.dart

@@ -5,6 +5,14 @@ import '../thermion_viewer_base.dart';
 enum Projection { Perspective, Orthographic }
 
 abstract class Camera {
+  Future lookAt(Vector3 position, {Vector3? focus, Vector3? up}) async {
+    focus ??= Vector3.zero();
+    up ??= Vector3(0, 1, 0);
+    final viewMatrix = makeViewMatrix(position, focus, up);
+    viewMatrix.invert();
+    await setModelMatrix(viewMatrix);
+  }
+
   Future setProjection(Projection projection, double left, double right,
       double bottom, double top, double near, double far);
   Future setProjectionMatrixWithCulling(

thermion_dart/lib/src/viewer/src/shared_types/render_target.dart

@@ -2,4 +2,5 @@ import 'package:thermion_dart/thermion_dart.dart';
 
 abstract class RenderTarget {
   Future<Texture> getColorTexture();
+  Future<Texture> getDepthTexture();
 }

thermion_dart/lib/src/viewer/src/shared_types/view.dart

@@ -23,7 +23,7 @@ enum QualityLevel {
 
 abstract class View {
   Future<Viewport> getViewport();
-  Future updateViewport(int width, int height);
+  Future setViewport(int width, int height);
   Future<RenderTarget?> getRenderTarget();
   Future setRenderTarget(covariant RenderTarget? renderTarget);
   Future setCamera(covariant Camera camera);