public float setRotateLeft() {
        if (documentViewModel == null) {
            return -1;
        }
        float viewRotation = documentViewModel.getViewRotation();
        viewRotation += ROTATION_FACTOR;
        viewRotation %= 360;
        documentViewModel.setViewRotation(viewRotation);
        documentViewScrollPane.revalidate();
        return viewRotation;
    }