public class ScrollWheelZoomer implements InputProcessor {

    private final OrthographicCamera camera;
    private boolean isEnabled;

    public ScrollWheelZoomer(OrthographicCamera camera) {
        this.camera = camera;
        this.isEnabled = true;
    }

    public void setEnabled(boolean enabled) {
        this.isEnabled = enabled;
    }

    @Override
    public boolean scrolled(int amount) {

        if (!this.isEnabled) {
            return false;
        }

        if (amount > 0 && camera.zoom < 10) {

this.scrollWheelZoomer = new ScrollWheelZoomer(this.camera);
this.scrollWheelZoomer.setEnabled(true);
this.inputHandler.addProcessor(new GestureDetector(this.cameraPanner));
this.inputHandler.addProcessor(new GestureDetector(this.pinchZoomer));
this.inputHandler.addProcessor(scrollWheelZoomer);
Gdx.input.setInputProcessor(this.inputHandler);