code: protected void setStageViewport() {
          if (context.isAvailable(Viewport.class)) {
              stage.setViewport(context.get(Viewport.class, stage));
          } else {
              Gdx.app.debug(Lml.LOGGER_TAG, "No provider found for Viewport.class. Using default Stage viewport.");
          }
          final Viewport viewport = stage.getViewport();
          centerCamera = viewport instanceof ScreenViewport || viewport instanceof LetterboxingViewport;
      }
docs: Called by the {@link #create()} method to set {@link Viewport} instance of the GUI {@link Stage}.