This graph suspiciously looks very

This graph suspiciously looks very similar to our input delay model. That’s because it’s basically the same except that we’re waiting for input data from a different frame! In this case, the current frame minus the rollback amount determines the frame that we acquire data from.You might notice this is parallel here: Input delay is done by adding to the frame before it is sent, rollbacks are done by subtracting from the current frame before getting the input. This way, not only can you mix the two as you see fit, as long as the input delay and amount of rollbacks sum to at least the necessary amount of input delay, the performance will be smooth and clean. Magic!I’m not going into the details of writing the rollbacks themselves into the game engine in this article, but assuming you have that part, that is literally the only change you need to make in order to make them work.But of course, if you have rollbacks, you have what is fundamentally a partially asynchronous networking model. This means you can do some extra magic tricks on top that you couldn’t do before!simple graph showing how rollbacks hide packet lossBecause of the way the model works, if you’re willing to rollback a few more frames than is set, you no longer need any sort of extraneous input buffer to keep everything running along smoothly. Instead you can just keep the game running like normal and then do a couple extra frames of rollback when the data is finally received.Obviously you want to put a reasonable limit on this so you don’t end up one second out without the correct input. RollCaster allows only one extra frame of rollback before forcing a block for input and forcing resynchronization. GGPO will run along for quite awhile as long as it can keep verifying that both systems are running at the same timing.And if you’re wondering, the rule from above regarding keeping synchronization with the other system’s performance must be upheld. If you detect that the other computer is running slowly and has dropped a frame, then you must also wait a frame to keep synchronization, even in a rollback setup. If you don’t do this the two computers will slowly drift out of timing and nobody wants that.That’s pretty much all I got!Once you have all that understood the remainder is simply setting up the network connection and figuring out how you’re going to do the rollbacks themselves, if you bother with them at all. And while this is all pretty optimized for 2 players, it doesn’t scale up to more cleanly without a real hassle, so be careful.