When you create a game, you need to consider the target framerate of your application: it will affect the entire dynamic of the physics engine and all the choices that will make the game playable. However, given the big heterogeneity of modern graphics cards with different types of monitors, the target frame rate may not be available on all configurations. It's therefore necessary that the target frame rate is scaled adequately to make the graphics equally fluid and to not affect the gameplay dynamics.
The demo presents one of the existing solutions for solving this type of problem, based on the frame adaptation with linear interpolation for the trajectory correction. In practice, the application frame rate is the vsync frame rate, while the target frame rate is used to calculate deltaT. A linear interpolation of the trajectories is used to bridge the gap between the target frame rate and the vsync frame rate, generating frames that do not exist to reach the vsync frame rate. As consequence, the F1 option is smoother than the F2 option.
