code: public void updateScale() {
          scaleX = targetPpiX / Gdx.graphics.getPpiX();
          scaleY = targetPpiY / Gdx.graphics.getPpiY();
      }
docs: Forces update of current pixel per unit ratio according to screen density.
  
  @see com.badlogic.gdx.Graphics#getDensity()
  @see com.badlogic.gdx.Graphics#getPpiX()
  @see com.badlogic.gdx.Graphics#getPpiY()