Відео

I appreciate the feedback. I did indeed use Core-A-Gaming's rollback demo footage from Punch Planet. In retrospect I should have been clearer on my source as I was with the GDC talks. Core-A-Gaming's video is made to inform players of the benefits of rollback to players, mine does need to do that as an introduction for people who don't know about rollback (e.g. my Uni lecturer marking my assignment) but is mostly aimed at developers + discussing implementation details. Outside of that footage I don't think it's fair to say the content, demos or phrasing are the same. Core-A-Gaming's video is not the basis of my video, though part of it was used to provide context, as with other existing videos from GDC and others. My video was made to showcase my own rollback implementation for a University assignment, and my use of footage would fall under Fair Use. If I (re)made the video today, I would do a lot of things differently. I didn't expect it to get the attention it did but I'm thankful for all the feedback from everyone. One day I'll get around to making another video :D

Sending previous inputs let's you fix incorrect predictions due to lost inputs. But with too high packet loss it won't be stable. You only need to send previous inputs up to your max allowed number of rollback frames so it shouldn't cause too much additional network traffic. It's not a problem I've tried to implement a solution for personally though. Best of luck.

@zacpeel-yates7276 Oh yeah for sure, and thanks for the reply. Didnt expect to get a reply on a year old video to be honest LOL. I definitely will limit the accepted number of rollback frames and maybe try to add in delay or something if it exceeds that, and probably disconnect if the lag is too much. If each frame is 4 or so bytes then it should hopefully be ok, i think, im a beginner at this so im not really sure but 4*10 bytes doesnt sound like a lot to transmit. I really do wonder how AAA studios do it... either way this video is a great resource though so thanks for that too!

I was mostly looking at Unity's Netcode for Game Objects, Mirror and Photon. They It's been a while so I couldn't tell you the exact reasons I dismissed each but in the end this was a University assignment so doing it myself gave me a better understanding of rollback system (and a better grade lol). I haven't looked into coherence too in depth but they have a section of theirs docs specifically for rollback which seems very useful: docs.coherence.io/coherence-sdk-for-unity/input-prediction-and-rollback

GGPO was originally written in C++ so you may be able to port it over, and there are existing plugins for UE4 if you don't want to roll your own: github.com/BwdYeti/GGPOUE4

@@zacpeel-yates7276 im actually making a fighting game in unreal, but i know almost nothing about multiplayer. so its been a struggle. thanks for the info.

It allows for my game sim to update at whatever frequency I want and for that frequency to be able to change if you end up too far behind and need to catch up, or slow the game sim down for other player to catch up. It should be possible to get something working within Unity's FixedUpdate -- just not the way I chose to go about things. My project really only uses Unity as a way to render out the gamestate. Again, not the only way to do it just the method I went for to ensure good decoupling.

This is known as 'rift' and will lead to one-sided rollbacks for the player with a higher frame-rate as inputs will be arriving to them late. Their inputs will arrive to the opponent ahead of time as the opponent is lagging behind, meaning the game will never be predicting ahead or rolling back. While handling this was outside of the scope of my implementation, having the game simulation and rendering decoupled means hopefully we can hit 60 game logic updates per second regardless of the visual frame-rate, and my code can handle changing update rates already in order to simulate multiple game logic updates within a render frame when correcting mispredictions . If the CPU is overheating and throttles itself though, it will slow down regardless. If it's only temporary we can rewind the gamestate back to the last point the players were synced, or try to sync in between (player A is on frame 12, player B is lagging behind on frame 8 - should try to sync both players on frame 10 ). MKX does this by lengthening the frames of the player who is ahead slightly in order to allow for the other player to catch up, then everything is put back to normal. If player As frames are briefly taking 20ms (50 FPS) instead of 16.67ms (60FPS) its gonna be pretty unnoticeable, but you net a frame of catchup every 5 frames. If it's consistently running at a lower framerate though (especially something like 30FPS vs 60FPS) its not gonna be a fun experience I'd imagine. Easiest 'solution' would be to force both players to be at the lowest update rate as you said, but then you either lose precision in the simulation - which will cause issues -or have players play in slow-motion - which is not fun. At that point its more of a question of optimization or ensuring ur minimum recommended specs for the game can consistently hit 60FPS on low graphics settings. Eventually though you would just need to accept the players aren't able to have a fair game under the current conditions and disconnect them for quality of service. (MKX does this at about 300 ping, not sure how they factor rift in) Here's a link to Tony Cannon's implementation ( GGPO, C++) where they handle this problem: github.com/pond3r/ggpo/blob/master/src/lib/ggpo/timesync.cpp Here's the excellent Core-A-Gaming talking with Tony about rift (timestamped, but the whole video is good): ua-cam.com/video/0NLe4IpdS1w/v-deo.html PS. Of course its ok for you to ask! Hope this helps.

They aren't synced outside of trying to keep inputs and current gamestate synced by fixing mispredictions with rollbacks. If a client finds that the remote kicked 4 frames ago, they can just have the animation on their end start on frame 4 if that makes sense. I'm not sure how Unity handles starting animations from arbitrary points but it should be possible. I think if you can keep everything synced up it should be fine. Personally I think it's cleanest to decouple any game-affecting data (hitboxes and their positions) from animation so that u can run the hitbox stuff in the simpler game simulation. I know MK has hitboxes attached to the bones of the models so there might be some better info here: ua-cam.com/video/7jb0FOcImdg/v-deo.html They also talk about handling stuff like projectiles, bunch of stuff I didn't manage to cover in my network test.

@@zacpeel-yates7276 Ah of course, if you don't attach hitboxes to the bones of the models there's no need to do that. For my game I'm thinking about making a table that has the bone positions/rotations for every frame of the animation, and then referencing that instead of using the bone's positions at runtime. This is to make sure that (1) the numbers aren't different across devices, but (2) also because of some weird bug where when I rotate/scale the character on the right side to face the other direction, the bone positions would be ever so slightly different meaning that, for example, if two players punch at the exact same time at a specific distance from one another, only the player on the left will get hit. Also I'm glad to hear you passed your assignment with flying colours! (how could you not, this is just amazing). I wish you the best for your future

@@djjimmaster8261 Thanks! Saw some of the stuff on your channel and it's looking good! Having a pre-made table of positions for each frame in the animation that you can reference is a good idea actually. Maybe could build some kind of editor script that lets you take an animation and convert it to a table of values that is serialized to a file for reference at runtime. Best of luck with your implementation!

@@zacpeel-yates7276 Thanks! I'm not very good at doing editor stuff yet (am quite new to Unity) so I was just thinking of playing the animation during runtime lol. But maybe I should try looking into making an editor script for it, would be an interesting challenge!

Nice!! You deserve it. This is absolutly the best video I have seen on the subject and super well presented.

Thanks for the feedback! Let me know if you have any further questions.

Let me know how you got on, I can try to answer any questions you have.

So I've been playing around with this project, to implement it into my own game, and it's going pretty well! But I get a weird bug inside the Game sim, when it comes to the actual rollback, maybe you can help me out? Inside the HandleRollbacks function, when I get the GameState to rollback, suddenly the SimPlayers of that GameState become null. We still have the GameState itself and the FrameID. Any help would be appreciated! I'll keep searching for the problem, and let you know if I find anything.