code: public void resize(final int width, final int height, final boolean centerCamera) {
          stage.getViewport().update(width, height, centerCamera);
      }
docs: Updates stage's viewport.
  
  @param width new width of the screen.
  @param height new height of the screen.
  @param centerCamera false by default. Some viewports seem to require it to be true for proper behavior (
  {@link com.badlogic.gdx.utils.viewport.ScreenViewport}, for example).