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programming is cool they said it'll be
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fun they said
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look i don't know who they is in this
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scenario but they forgot to mention that
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you can spend two days trying to figure
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out why your code isn't working
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wondering if your brain is
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malfunctioning and just before you go
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completely insane you realize that you
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didn't read the documentation properly
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and all it takes to fix it is changing
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one word
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ah yes the joys of programming
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so
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yeah making multiplayer games kinda
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sucks
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over the last few weeks i've been
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working on re-implementing client
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prediction into my game and player
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movement is once again nice and
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responsive but why was the movement
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unresponsive in the first place and what
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the heck is klein prediction well let me
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introduce you to the arch enemy of all
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game developers that are working on
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multiplayer games latency
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you're able to watch this video right
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now because youtube servers are sending
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the video's data to your web browser
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however this doesn't happen instantly as
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it takes time for that data to
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physically travel from youtube to your
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computer
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that travel time doesn't really make a
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difference when you're watching a video
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or stealing someone's code but if you're
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building a fast-paced multiplayer game
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where reaction speed is critical latency
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will literally make your job go from
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easy to pure pain and suffering
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imagine light travel 299 million 792 458
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times slower than it actually does or at
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one meter per second now imagine you're
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standing a meter away from someone if
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that person took a step to the right you
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would only see them start to move an
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entire second after they actually
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started moving this is essentially the
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same problem that games face because by
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the time your computer is told that
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another player moved that information is
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already outdated you can probably figure
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out for yourself why that would cause
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major problems in games like first
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person shooters where even a fraction of
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a second of delay in another player's
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position could cause you to be aiming at
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nothing seriously when they were
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creating the internet who decided that
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latency was a good feature to add
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in this video though i just want to talk
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about movement a little delay wouldn't
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make movement unresponsive on your end
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right you could just have every player's
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computer calculate and update their own
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position the same way single player
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games do it players would still see each
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other in the past but at least they
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would see themselves move immediately
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after pressing a key
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unfortunately this is where the second
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half of the problem comes in cheaters
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you can't trust your players because a
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certain amount of them will happily
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exploit anything they can and often this
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will ruin the experience for other
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players to prevent things like speed or
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fly hacks you need your game server to
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be the one calculating the movement for
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all players as it's the only thing you
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can trust
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unless of course you're an incompetent
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programmer in which case you can trust
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nothing
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so since the server has to handle your
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movement for you that means when you
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press the w key to move forward you have
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to wait for your computer to send that
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instruction all the way to the server
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then the server does the calculation
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updates your position and you have to
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keep waiting until that update finally
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makes it back to your computer all of
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that might happen in less than a tenth
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of a second but when you're at the
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controls even that seemingly tiny amount
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of delay can make the movement feel
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sluggish this is where client prediction
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comes to save us the idea here is to
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have the client which is your computer
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and the server both calculate your
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movement while you're waiting for the
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server to receive your input calculate
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the proper movement and send back the
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result your computer will also calculate
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the movement and update your position
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accordingly which means that when you
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press a key you will move immediately
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then when the server eventually sends
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back what it determined to be your new
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position we have your client compare
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that correct position to what it had
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predicted for the same point in time if
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they match which should be the case most
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of the time for a non-cheating client
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then all is well with the world if they
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don't match the position needs to be
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corrected but because nothing is allowed
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to be simple when developing a
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multiplayer game it's obviously not as
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easy as just overwriting your current
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position
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since your current position is predicted
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and therefore essentially from the
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future and the position from the server
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is technically in the past the two can't
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just be compared because when you're
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moving they actually should be different
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we're basically dealing with multiple
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time streams meaning that time travel
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doesn't just happen in books and movies
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your computer is constantly doing it
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every time you play a fast-paced
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multiplayer game i won't go into any
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more detail though because this is the
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point where things get even more
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complicated and confusing and i'd rather
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get back to the practical side of things
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remember how at the beginning of the
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video i said player movement is once
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again nice and responsive well i lied
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sort of the movement is smooth and
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responsive on land but
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this is what happens when you step on a
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boat why remember our good friend
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latency yeah me neither because latency
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is the enemy not our friend since the
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server is the one calculating the
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movement for the ships by the time a
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position update reaches your computer
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it's already outdated that means that
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when you try to predict your movement
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from onboard a boat you're doomed to
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fail because you're working with a
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different starting position than the
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server is it's kind of like taking two
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calculators and punching in different
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numbers then adding one
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even though you added one to both the
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result will never be the same because
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the starting numbers were different
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basically you end up constantly
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mispredicting your position which then
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triggers a correction and sometimes that
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correction will put you inside the
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ship's collider because the ship
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position is outdated and then the
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physics system loses its mind because
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colliders aren't allowed to be inside
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one another but then that puts you in
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the wrong position again so another
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correction is triggered immediately
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afterwards and it causes a vicious cycle
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of violent jittering
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so through the power of editing you've
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been spared several more weeks of me
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questioning why i decided to build a
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multiplayer game or get into programming
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in the first place but i'm pleased to
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announce that i have successfully made
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predictions smooth
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even on boats since my prediction works
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on dry non-moving land i just made the
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boat also not move i have this duplicate
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of the ship way under the water where no
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one will ever run into it and when you
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step onto the actual real moving boat
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both the client and the server start
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using this proxy to calculate your
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movement you can think of it like being
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teleported onto the duplicate boat
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except visually you still see yourself
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moving on the real one since the proxy
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doesn't move there's no incorrect
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predictions to deal with except when
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getting on and off of boats because
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that's when the system has to change
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where and how it's calculating movement
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the way it is now the jitter is pretty
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noticeable when you jump off a boat but
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since it's only for a moment i think a
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bit of smoothing should be able to hide
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it quite well
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anyways i'm super relieved that i
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finally got this working but of course
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i'm building a multiplayer game so i
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need to make sure to test this with more
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than one player connected at a time
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[Music]
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[Music]
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you
