programming multiplayer game - wordpress.com · 2013-10-10 · phoenix area game developer since...

Multiplayer Game Programming

David Koontz@dkoontz

dkoontz.wordpress.com

● Phoenix area game developer since 2001● Teacher at Art Institute since 2006● Worked on a variety of educational and

commercial games● Author of iTween Visual Editor and

CameraFor2D components for Unity● Currently developing Star. Ship. Story., a

co-op space faring adventure○ Slightly crazy to be making a

multiplayer game

How the Internet worksSpecial considerations for gamesUsing a library vs writing your ownExisting tools for Flash, C#, HTMLQuestions

Content Packet Header

How the Internet worksSpecial considerations for gamesUsing a library vs writing your ownExisting tools for Flash, C#, HTMLQuestions

Content Packet Header

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

?

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Problem

A B

The Internet functions by being able to break data (usually cats) into “packets” and then (semi)reliably delivering those packets to their destination using whatever networks are available.

IP Protocol

Destinations are numbered addresses that look like this:

127.0.0.1192.168.0.10068.105.28.11

The “protocol” bit of the “IP Protocol” is just the expected actions of each party participating in the exchange and an agreed upon way of interpreting data sent between the systems

What is a protocol?

What is a protocol?

Shaking hands when meeting someone is a social protocol. Signalling before changing lanes is standard driving protocol. “Belay, on belay, belay on” is standard rock climbing protocol.

The “protocol” bit of the “IP Protocol” is just the expected actions of each party participating in the exchange and an agreed upon way of interpreting data sent between the systems

It’s protocols all the way down

TCP

ReliableOrdered

Maintains a connectionNeeds handshake

Fetching a web siteTransferring a fileChat messages

Turn based games

UDP

UnreliableUnordered

ConnectionlessLess overhead per packet

Voice chatMost high action games

Anything severely affected by latency

IP

Both TCP and UDP add another element to the “where” part of delivering a packet

Ports

68.105.28.11:3724

Both TCP and UDP add another element to the “where” part of delivering a packet

Ports

68.105.28.11:3724

IP address Port

Ports allow the receiving computer to differentiate the packets coming in for one application vs another

Ports

Ports

Think of how many applications you have receiving data at once through the same network connection

Ports

Web browser AIM PandoraSkype MSN SpotifySystem updates GChat Games

The anatomy of an IP packetTo

tal l

engt

h, p

roto

col

num

ber,

othe

r im

porta

nt

but b

orin

g va

lues

Sou

rce

IP a

ddre

ss

Des

tinat

ion

IP a

ddre

ss

Dat

a

Por

t, H

ands

hake

info

, se

quen

ce n

umbe

r, et

c.

Header

The anatomy of an IP packetTo

tal l

engt

h, p

roto

col

num

ber,

othe

r im

porta

nt

but b

orin

g va

lues

Sou

rce

IP a

ddre

ss

Des

tinat

ion

IP a

ddre

ss

Dat

a

IP Protocol Your application’s protocolTCP/UDP

Por

t, H

ands

hake

info

, se

quen

ce n

umbe

r, et

c.

16 bytes 16 bytes /4 bytes

The data that is sent mustbe converted to a format that can be sent across the Internet.

The process of converting your data to this format is called serialization

Serialization (aka marshalling)

Dat

a

The serialized form of your data is always a byte array

Serialization

int

bool

float

string

serializer byte[ ]

Deserialization is just the opposite process, extracting specific bits of data from the byte array as an int / float / string / etc.

Deserialization

int

bool

float

string

deserializerbyte[ ]

You must know the format of the data that was serialized so that you can deserialize it correctly

Deserialization

float

bool

int

string

deserializerbyte[ ]

You must know the format of the data that was serialized so that you can deserialize it correctly

Deserialization

float

bool

int

string

deserializerbyte[ ]

How the Internet worksSpecial considerations for gamesUsing a library vs writing your ownExisting tools for Flash, C#, HTMLQuestions

Content Packet Header

The game state is all the significant values needed in order for the game to operate.

Position / RotationPlayer itemsEnemy actionTime remaining

State

All input can be processed on the same frame/update

There is only one game state

Cheating is handled by the players themselves

Input arrives inconsistently from clients

There are (# of player) game states

Cheating must be handled by the game

Local vs Internet multiplayer

Unlike local multiplayer, each client has a unique but similar game state

Mostly synched game states

Each player’s game must simulate the actions of the other players

Mostly synched game states

Sometimes these simulations are wrong

Mostly synched game states

Life on the Internet == Latency (Lag)

The difficulty of keeping all the various clients synched up is directly related to the time sensitivity of your game.

Time sensitivity

The difficulty of keeping all the various clients synched up is directly related to the time sensitivity of your game.

Time sensitivity

Async TurnBased Game

Twitch FPS

Egads, are you daft?

A worthy challenge my lad

RTS Diablo / Torchlight

Tactical FPSMMORPG

Parlor games, chess, poker

I doff my hat do thee

A tale of two game statesPart 1

This seems pretty straightforward

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game statesPart 2

Or so I thought

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game states

Character moved, shot missed

Character was shot, movement is ignored

A tale of two game statesPart 3

A wild solution appears(It’s super effective)

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game states

A tale of two game statesFin

Ok, maybe not super effective

A tale of two game states

60ms

A tale of two game states

60ms

60ms

A tale of two game states

Waiting 120ms for your key press to be registered is a bad user experience

People expect immediate response times, especially in an action oriented game

Delayed input

Extrapolation

Extrapolation

Extrapolation

This technique allows the local machine to feel responsive, while still allowing the server to be authoritative

It may lead to snapping or “rubber banding” if the server’s version of the player’s position is different from what the local simulation predicted

Extrapolation

Interpolation

Interpolation

Interpolation

Allows the client to fix errors over a short time, largely hiding the error

When combined with extrapolation, can result in very smooth looking gameplay, even under higher lag conditions

Interpolation

Extrapolating other clients

Extrapolating other clients

Extrapolating other clients

Extrapolating other clients

Extrapolating other clients

Extrapolating other clients

Extrapolating other clients

Example videos

ClientImmediate processing of input

Easy to cheat

Can result in inconsistent states

ServerMust wait for server to acknowledge input

Client are told the result of their own input

Server must be able to simulate the game

Client vs server authority

● This means you can not trust ANYTHING the client sends you

● Clients are generally not allowed to communicate directly

● Clients make requests to the server to perform an action which the server carries out if that is ok○ Is it ok for this client to be requesting this action?○ Client A using item owned by Client B

The authoritative server

Keep the server game logic isolated from the server “network” logic.

Allows you to upgrade these parts in isolation from each other

Suggestion

One approach to server logic

Server network logic

A

B

C

Server game logic

byte[]

Player “Ub3r1337”

wants to jump

One approach to server logic

Server network logic

A

B

C

Server game logic

Ok

OkPlayer “Ub3r1337”

jumped

Player “Ub3r1337”

jumped

Depending on your game’s needs, that server might be a web server (http get/post), a socket server (real time communication) or some mixture of the two

It all depends

Depending on your game’s needs, that server might be a web server (http get/post), a socket server (real time communication) or some mixture of the two

It all depends

Async TurnBased Game

Twitch FPS

UDP, socket server

HTTP over TCPPHP, Ruby on Rails, MVC.NET

RTS Diablo / Torchlight

Tactical FPSMMORPG

Parlor games, chess, poker

Socket server over TCP or UDP

Depending on your game’s needs, that server might be a web server (http GET/POST), a socket server (real time communication) or some mixture of the two

It all depends

Async TurnBased Game

Twitch FPS

UDP, socket server

HTTP over TCPPHP, Ruby on Rails, MVC.NET

RTS Diablo / Torchlight

Tactical FPSMMORPG

Parlor games, chess, poker

Socket server over TCP or UDP

More off the shelf solutions Need custom solution

How the Internet worksSpecial considerations for gamesUsing a library vs writing your ownExisting tools for Flash, C#, HTMLQuestions

Content Packet Header

● Structure!

What does a library do for you?

● Structure!● Message protocol

What does a library do for you?

● Structure!● Message protocol● Serialization & deserialization

What does a library do for you?

● Structure!● Message protocol● Serialization & deserialization● A structure for client lifecycle events

What does a library do for you?

● Structure!● Message protocol● Serialization & deserialization● A structure for client lifecycle events

○ Connection / disconnection○ Authentication○ Chat○ Saving / retrieving user data○ Payments

What does a library do for you?

● Structure!● Message protocol● Serialization & deserialization● A structure for client lifecycle events

○ Connection / disconnection○ Authentication○ Chat○ Saving / retrieving user data○ Payments

● Can provide a tie-in to hosting solutions

What does a library do for you?

● You need to use their server and client libraries○ Both ends must be able to speak the same

protocol

What does a library impose on you?

● You need to use their server and client libraries○ Both ends must be able to speak the same

protocol● May only be available for certain

languages or platforms

What does a library impose on you?

● You need to use their server and client libraries○ Both ends must be able to speak the same

protocol● May only be available for certain

languages or platforms● May be closed source and / or commercial

What does a library impose on you?

● You need to use their server and client libraries○ Both ends must be able to speak the same

protocol● May only be available for certain

languages or platforms● May be closed source and / or commercial● May impose limitations on how you deploy

or structure your server

What does a library impose on you?

● Requires more familiarity with lower level network concepts (sockets, etc.)

Rolling your own

● Requires more familiarity with lower level network concepts (sockets, etc.)

● Requires you to put in place a structure for your server and client

Rolling your own

● Requires more familiarity with lower level network concepts (sockets, etc.)

● Requires you to put in place a structure for your server and client

● Requires you to develop your own message protocol and serialization / deserialization procedures

Rolling your own

It depends!

So which is better?

It depends!

No really, that’s my entire answer

So which is better?

How the Internet worksSpecial considerations for gamesUsing a library vs writing your ownExisting tools for Flash, C#, HTMLQuestions

Content Packet Header

Server as standalone

SmartFox (Java)Photon (C#)ElectroServer (Java)Player.IO (C#)Lidgren (C#)Flash Media ServerRed5 (Java)

Server as special client

uLink (Unity)Built in UnityBadumna (Unity)

Two types of solutions

● Can be written in a language more appropriate for writing a server

Standalone server

● Can be written in a language more appropriate for writing a server

● Can be used with any language / platform there is a client library for (or that you’re willing to develop a client library for)

Standalone server

● Can be written in a language more appropriate for writing a server

● Can be used with any language / platform there is a client library for (or that you’re willing to develop a client library for)

● Needs to implement all the important logic of your game, and may not be able to reuse the same code from your client

Standalone server

● Can be written in a language more appropriate for writing a server

● Can be used with any language / platform there is a client library for (or that you’re willing to develop a client library for)

● Needs to implement all the important logic of your game, and may not be able to reuse the same code from your client

● Can be as light or heavy weight as you need

Standalone server

● Only one place to put the logic

Client as server

● Only one place to put the logic● Both client and server are the same app

and can share logic

Client as server

● Only one place to put the logic● Both client and server are the same app

and can share logic● Allows players to host games easily as

well as running dedicated hosts

Client as server

● Only one place to put the logic● Both client and server are the same app

and can share logic● Allows players to host games easily as

well as running dedicated hosts● Must interface with some sort of front end

to manage user sessions

Client as server

● Only one place to put the logic● Both client and server are the same app

and can share logic● Allows players to host games easily as

well as running dedicated hosts● Must interface with some sort of front end

to manage user sessions● Might have high overhead of running your

game client when not all of it is needed

Client as server

● Only one place to put the logic● Both client and server are the same app

and can share logic● Allows players to host games easily as

well as running dedicated hosts● Must interface with some sort of front end

to manage user sessions● Might have high overhead of running your

game client when not all of it is needed● Keeping client and server code separate

can be tricky

Client as server

Family Guy Online

Hybrid

A

B

C

Photon

Unity

Unity

D

● The Internet is a modern marvel, but is not a panacea

● Internet multiplayer is a good way to make your game 10x more complex

● There are no general solutions, only specific answers to specific problems

Summary

How the Internet worksSpecial considerations for gamesUsing a library vs writing your ownExisting tools for Flash, C#, HTMLQuestions

Content Packet Header

David Koontz@dkoontzdavid@koontzfamily.orghttp://dkoontz.wordpress.comhttp://happycamperstudios.com

Send complaints to: