While scrolling the game screen, it isn't clear because of afterimages.
It is not a serious problem but, I want to fix this.
I guess this problem related with double buffering.
I'm already using vertical sync, but it doesn't help to fix this problem.
I'm using sf::View to scroll the screen.
Here's some sample code.
// view.move(0.f, 1.f); // this works well
// view.move(0.f, 2.f); // this works well too
view.move(0.f, 3.f); // the problem happens here
window.clear();
window.setView(view);
window.draw();
window.display();
Thanks