Preserve state when switching renderers

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_renderer/lib/base_renderer.dart

@@ -23,7 +23,6 @@ abstract class BaseWolfRendererState<T extends BaseWolfRenderer>
   @override
   void initState() {
     super.initState();
-    // DO NOT initialize the engine here. Just start the loop!
     gameLoop = createTicker(_tick)..start();
     focusNode.requestFocus();
   }
@@ -31,10 +30,14 @@ abstract class BaseWolfRendererState<T extends BaseWolfRenderer>
   void _tick(Duration elapsed) {
     if (!widget.engine.isInitialized) return;
 
+    if (_lastTick == Duration.zero) {
+      _lastTick = elapsed;
+      return;
+    }
+
     Duration delta = elapsed - _lastTick;
     _lastTick = elapsed;
 
-    // Tick the shared engine
     widget.engine.tick(delta);
 
     performRender();