I added QCPItemLine to my graph. I have two buttons in my graph. one of them move QCPItemLine to forward and other move QCPItemLine to backward. Each time I call replot() function to update QCPItemLine coords. But my graph has 2000 x values and replot() works slowly when I click button in series. Actually nothing change in graph except x coord of QCPItemLine. Is there any smart way to solve this?