If you’ve at least skimmed the headlines of our EVO 2022 related news, you’ve probably seen the word spread rollback many times since Persona 4 Arena Ultimate, Samurai Shodown and Dragon Ball Fighter Z have each announced to get started.
We thought it might be useful to offer you an article that explains what it is and why it is so important to help the uninitiated to have a vague idea of the situation without going into details. And let’s admit that it will make a useful link for the next mentions of the word in our news and our tests. What does the term rollback mean? We answer your question what is rollback (and why it matters in fighting games).
The special relationship of fighting games to online
Know first that this article will address the subject of online gambling and its technical part. We are not going to go into details but we can go online in two ways, by directly connecting the players to each other (peer-to-peer) or by connecting them to the same server which will therefore be responsible for managing the set of data. Other genres generally use the server given the number of players (imagine connecting to 99 machines for Fortnite for example).
The case of fighting games is therefore special for two reasons. On the one hand, the number of players is much more limited (and we are not looking to increase it). And on the other hand, this genre requires a much higher level of precision than the rest. We call netcode all the technologies put in place to allow the online game of a particular title. And so it’s a very guarded aspect in the world of Versus Fighting.
Especially since the start of the pandemic with the difficulty of organizing physical events. The competitive scene needed the best netcode until players could once again gather and travel to compete in the various tournaments. For pro players, being able to train remotely in conditions similar to the local game changes a lot of things.
This has an impact on the games since if the most famous people in the fighting game community can train more and create content online, it helps in the communication of the title which has an impact on the population on the servers, sales of the game and its DLCs, which can extend its support and avoid the dreaded categorization of “dead game” for as long as possible.
Delay-Based Netcode
The classic type of netcode, used by the entire genre until the beginning of rollback’s democratization in the 2010s, is delay-based netcode. During an online game, everyone does not necessarily have the same latency (or ping, the response time between their machine and the server or their opponent’s machine). So to go to the simplest, the game will stall on the person who has the most ping in the game and slow down the others.
Fighting games are frame-based, the faster an animation starts, the faster you can react. A frame lasts about 16 milliseconds, so a high ping creates an additional lag between the moment you enter a command on the controller or the arcade stick, and the moment the action starts on the screen. A difference compared to the local game that can change everything for professional players.
And even for ordinary mortals, the higher the latency, the higher the chances of lag (when the game appears to be slowing down) and freezes (when the image stops for a while). And when there is too much data loss in the communication, it can cause the disconnections. Developers can do what they can to optimize their system, it won’t help if a player has a bad ADSL connection and/or bad Wifi.
The famous rollback
The rollback is a bit of a method based on the expression “better to ask forgiveness than permission”. Indeed, in this type of netcode, your machine tries to predict what will happen so as not to slow down the action and then asks for confirmation to know if it got it right and correct the situation a little if necessary. So in theory as long as the predictions are correct, you shouldn’t see any differences with offline play.
The hope is that the delay is so short between two checks that the action could not have differed so much for the two players so that the corrections are almost invisible to the naked eye even in the event of errors. Therefore, in the event of a perfect connection for each player, we do not feel that much of a difference, but it is especially in the case of poor connections or very long distances that rollback can make online games much more pleasant.
It is not a miracle solution since it causes or reinforces other types of problems. Because yes surprisingly, the rollback can cause a problem known as rollback (when a player seems to go back in time). In some cases, the accumulation of differences between the two players can lead to desynchronizations where they no longer play against each other but rather against an alternative ghost, even if it means ending up with a different result in extreme cases.
But why doesn’t everyone go straight to rollback?
It will surprise you, but creating a system that only sends and receives information is much easier than creating a system that must guess the future. It’s obviously much more complicated and more expensive to set up and you also have to take into account the fact that we are still in the early stages of this technology and that means that developers are trying it out for the first time.
There is also a big difference between American and Japanese studios on this point. At the risk of falling into the cliché, the United States is a huge country where the quality of Internet connections is more than uneven and Japan is a much more compact country with very good connections. The Japanese developers were therefore more reluctant since they were less directly concerned by the subject where the Americans are very familiar with the problem.
This is why we have seen such a wave of rollback announcements on Japanese games that have already been available for several years. Before the pandemic, community insistence on this point was not as strong. To redo an online from scratch to start on such a different netcode is obviously very complex for games that are already available. This explains why the change often does not pass a beta phase.