public void setCurrentViewport(float left, float top, float right, float bottom) {
        constrainViewport(left, top, right, bottom);
    }
public void setCurrentViewport ( float left , float top , float right , float bottom ) { constrainViewport ( left , top , right , bottom ) ; }
Set new values for curent viewport, that will change what part of chart is visible. Current viewport must be
equal or smaller than maximum viewport.