public void constrainViewport(float left, float top, float right, float bottom) {
        super.constrainViewport(left, top, right, bottom);
        viewportChangeListener.onViewportChanged(currentViewport);
    }
Version of ChartComputator for preview charts. It always uses maxViewport as visible viewport and currentViewport as
preview area.
hellocharts-library/src/lecho/lib/hellocharts/computator/PreviewChartComputator.java