Game network programming

Game network programmingPotHix (Willian Molinari)Diego Souza (marciano)

Why?

Skeleton Jigsaw: http://plaev.me/skeleton-jigsaw

Shameless self promotion

To have fun, bro!

■ Synchronous RTS

■ Peer to peer

■ Client / server

■ UDP

■ Quake strategy

■ TCP

■ Web and HTML5

Agenda

Synchronous RTS

RTS's and Supreme commander

Peer to peer

Everything in sync

Two gameloops!

LatencyMy life for the horde!

Player1 Player2 Player3

tick 100ms

tick 200ms

tick 300ms

tick 400ms

tick 0ms

Player1 Player2 Player3

tick 100ms

tick 200ms

tick 300ms

tick 400ms

tick 0ms

Player1 Player2 Player3

tick 100ms

tick 200ms

tick 300ms

tick 400ms

tick 0ms

Player1 Player2 Player3

tick 100ms

tick 200ms

tick 300ms

tick 400ms

tick 0ms

butterfly effect

So...

Player1 Player2 Player3

tick 100ms

tick 200ms

tick 300ms

tick 400ms

tick 0ms

Player1 Player2 Player3

tick 100ms

tick 200ms

tick 300ms

tick 400ms

tick 0ms

UI OK!

Desync

Age of empires1500 archers with a 28.8 modem [1]

Client / Server

Authoritative server

Client Server

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

move

pos (1,0)

Client Server

pos (0,0)

pos (0,0)

move

pos (1,0)

pos (1,0)

Smartass

Client Server

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

move

pos (100,200)

Client Server

pos (0,0)

pos (0,0)

move

pos (100,200)

pos (100,200)

Client Server

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

pos (1,0)

Victory!

Client side prediction

Client Server

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

pos (1,0)

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

pos (1,0)

Latency

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

pos (1,0)

Animation

Predicting

Client Server

pos (0,0)

pos (0,0)

move right

pos (1,0)

pos (1,0)

Animation

Predicting

Client Server

pos (0,0)

pos (0,0)

move right

pos (2,0)

pos (1,0)

Animation

Client Server

pos (0,0)

pos (0,0)

move right

pos (2,0)

pos (1,0)

Animation

pos (2,0)

Correction

Quakehttps://github.com/id-Software

UDPdatagrams, unreliable, unordered

rcv_buf >= snd_bufAll receive operations return only one packet

watch out for MSG_TRUNC

auto ip_mtu_discover enabled by default

EMSGSIZE signals packet too big

65k max theoretical packet limit (headers included)

rfc defines the size header to 16bits

however, 1472 is likely the max you may get, 576 to be

sureMTU - headers

remember the TOSthroughput, reliability, lowdelay (etc.)

Quake worldhttps://github.com/id-Software/Quake

All credits to Fabien Sanglard: http://fabiensanglard.net/quakeSource/quakeSourceNetWork.php

Code: https://github.com/id-Software/Quake/blob/master/QW/client/net_chan.c

Quake III arenahttps://github.com/id-Software/Quake-III-Arena

Snapshots based

All credits to Fabien Sanglard: http://fabiensanglard.net/quake3/network.php

All credits to Fabien Sanglard: http://fabiensanglard.net/quake3/network.php

All credits to Fabien Sanglard: http://fabiensanglard.net/quake3/network.php

All credits to Fabien Sanglard: http://fabiensanglard.net/quake3/network.php

All credits to Fabien Sanglard: http://fabiensanglard.net/quake3/network.php

All credits to Fabien Sanglard: http://fabiensanglard.net/quake3/network.php

Open source code!https://github.com/id-Software/Quake-III-Arena/blob/master/code/qcommon/msg.c

TCPStreaming, reliable, connection oriented

TCP tuning

Long story short: use auto-tune You probably just need to tune the maximum values

(system wide)

High-performance extensions

refer to rfc1323

Bandwidth-delay product data link's capacity (in bits per second) and its end-to-

end delay (in seconds).

10Mbs x 1ms = 1.22 KB10Mbs x 200ms = 244 KB

rfc1323: huge buffers

CORKdon't send partial frames

NODELAYdisable nagle's algorithm

socket options

https://gist.github.com/4036204

benchmarking

BBG* and HTML5*Browser based games

The same thing......but not...

No TCP No UDP

No peer to peer

Chrome support!?http://developer.chrome.com/apps/app_network.html

HTTP

Websockets

Mozilla multiplayer game: http://browserquest.mozilla.org

BrowsersIE

Firefox

ChromeOpera

Safari

Android browser

Mobile safari

Opera mini

Blackberry browser

Caniuse.com: websockets marketshare

Socket.ioFallbacks all over the place

BandwidthWe're back again

■ [1] Age of empires paper

■ Synchronous RTS engines

■ Client / server tricks

■ Quake code reviews

■ Improving bandwidth for websockets

■ Unreal networking architecture

■ http://tools.ietf.org/html/rfc1323

References

■ http://linux.die.net/man/7/udp

■ http://linux.die.net/man/7/ip

■ http://linux.die.net/man/7/socket

■ http://en.wikipedia.org/wiki/Nagle's_algorithm

■ http://en.wikipedia.org/wiki/Bandwidth-

delay_product

References

■ http://tools.ietf.org/html/rfc1046

■ http://linux.die.net/man/7/tcp

References

Game over