Multiplayer Game Programming

Transcription

1 Multiplayer Game Programming

2 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 David dkoontz.wordpress.com

3 Content Packet Header How the Internet works Special considerations for games Using a library vs writing your own Existing tools for Flash, C#, HTML Questions

4 Content Packet Header How the Internet works Special considerations for games Using a library vs writing your own Existing tools for Flash, C#, HTML Questions

5 The Problem A B

6 The Problem A B

7 The Problem A B

8 The Problem A B?

9 The Problem A B

10 The Problem A B

11 The Problem A B

12 The Problem A B

13 The Problem A B

14 The Problem A B

15 The Problem A B

16 The Problem A B

17 The Problem A B

18 The Problem A B

19 IP Protocol 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. Destinations are numbered addresses that look like this:

20 What is a 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

21 What is a 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 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.

22 It s protocols all the way down TCP UDP Reliable Ordered Maintains a connection Needs handshake Unreliable Unordered Connectionless Less overhead per packet Fetching a web site Transferring a file Chat messages Turn based games Voice chat Most high action games Anything severely affected by latency IP

23 Ports Both TCP and UDP add another element to the where part of delivering a packet :3724

24 Ports Both TCP and UDP add another element to the where part of delivering a packet IP address Port :3724

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

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

27 Ports Web browser Skype System updates AIM MSN GChat Pandora Spotify Games

28 Data Port, Handshake info, sequence number, etc. Destination IP address Source IP address Total length, protocol number, other important but boring values The anatomy of an IP packet Header

29 16 bytes TCP/UDP 16 bytes / 4 bytes Data IP Protocol Port, Handshake info, sequence number, etc. Destination IP address Source IP address Total length, protocol number, other important but boring values The anatomy of an IP packet Your application s protocol

30 Serialization (aka marshalling) The process of converting your data to this format is called serialization Data The data that is sent must be converted to a format that can be sent across the Internet.

31 Serialization The serialized form of your data is always a byte array int float serializer string bool byte[ ]

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

33 Deserialization You must know the format of the data that was serialized so that you can deserialize it correctly float int byte[ ] deserializer string bool

34 Deserialization You must know the format of the data that was serialized so that you can deserialize it correctly float int byte[ ] deserializer string bool

35 Content Packet Header How the Internet works Special considerations for games Using a library vs writing your own Existing tools for Flash, C#, HTML Questions

36 State The game state is all the significant values needed in order for the game to operate. Position / Rotation Player items Enemy action Time remaining

37 Local vs Internet multiplayer All input can be processed on the same frame/update Input arrives inconsistently from clients There is only one game state There are (# of player) game states Cheating is handled by the players themselves Cheating must be handled by the game

38 Mostly synched game states Unlike local multiplayer, each client has a unique but similar game state

39 Mostly synched game states Each player s game must simulate the actions of the other players

40 Mostly synched game states Sometimes these simulations are wrong

41 Life on the Internet == Latency (Lag)

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

43 Time sensitivity The difficulty of keeping all the various clients synched up is directly related to the time sensitivity of your game. MMORPG Async Turn Based Game Parlor games, chess, poker A worthy challenge my lad RTS Tactical FPS Diablo / Torchlight I doff my hat do thee Twitch FPS Egads, are you daft?

44 This seems pretty straightforward A tale of two game states Part 1

45 A tale of two game states

46 A tale of two game states

47 A tale of two game states

48 A tale of two game states

49 A tale of two game states

50 A tale of two game states

51 Or so I thought A tale of two game states Part 2

52 A tale of two game states

53 A tale of two game states

54 A tale of two game states

55 A tale of two game states Character moved, shot missed Character was shot, movement is ignored

56 A wild solution appears (It s super effective) A tale of two game states Part 3

57 A tale of two game states

58 A tale of two game states

59 A tale of two game states

60 A tale of two game states

61 A tale of two game states

62 Ok, maybe not super effective A tale of two game states Fin

63 A tale of two game states 60ms

64 A tale of two game states 60ms 60ms

65 A tale of two game states

66 Delayed input 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

67 Extrapolation

68 Extrapolation

69 Extrapolation

70 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

71 Interpolation

72 Interpolation

73 Interpolation

74 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

75 Extrapolating other clients

76 Extrapolating other clients

77 Extrapolating other clients

78 Extrapolating other clients

79 Extrapolating other clients

80 Extrapolating other clients

81 Extrapolating other clients

82 Example videos

83 Client vs server authority Client Immediate processing of input Server Must wait for server to acknowledge input Easy to cheat Client are told the result of their own input Can result in inconsistent states Server must be able to simulate the game

84 The authoritative server 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

85 Suggestion Keep the server game logic isolated from the server network logic. Allows you to upgrade these parts in isolation from each other

86 One approach to server logic A byte[] B C Server network logic Player Ub3r1337 wants to jump Server game logic

87 One approach to server logic A Ok B Player Ub3r1337 jumped Player Ub3r1337 jumped C Server network logic Ok Server game logic

88 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

89 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 MMORPG Async Turn Based Game Parlor games, chess, poker HTTP over TCP PHP, Ruby on Rails, MVC.NET RTS Tactical FPS Diablo / Torchlight Socket server over TCP or UDP Twitch FPS UDP, socket server

90 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 MMORPG Async Turn Based Game Parlor games, chess, poker HTTP over TCP PHP, Ruby on Rails, MVC.NET More off the shelf solutions RTS Tactical FPS Diablo / Torchlight Socket server over TCP or UDP Twitch FPS UDP, socket server Need custom solution

91 Content Packet Header How the Internet works Special considerations for games Using a library vs writing your own Existing tools for Flash, C#, HTML Questions

92 What does a library do for you? Structure!

93 What does a library do for you? Structure! Message protocol

94 What does a library do for you? Structure! Message protocol Serialization & deserialization

95 What does a library do for you? Structure! Message protocol Serialization & deserialization A structure for client lifecycle events

96 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

97 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

98 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

99 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

100 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

101 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

102 Rolling your own Requires more familiarity with lower level network concepts (sockets, etc.)

103 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

104 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

105 So which is better? It depends!

106 So which is better? It depends! No really, that s my entire answer

107 Content Packet Header How the Internet works Special considerations for games Using a library vs writing your own Existing tools for Flash, C#, HTML Questions

108 Two types of solutions Server as standalone Server as special client SmartFox (Java) Photon (C#) ElectroServer (Java) Player.IO (C#) Lidgren (C#) Flash Media Server Red5 (Java) ulink (Unity) Built in Unity Badumna (Unity)

109 Standalone server Can be written in a language more appropriate for writing a server

110 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)

111 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

112 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

113 Client as server Only one place to put the logic

114 Client as server Only one place to put the logic Both client and server are the same app and can share logic

115 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

116 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

117 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

118 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

119 Hybrid Family Guy Online A Unity B Photon C Unity D

120 Summary 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

121 Content Packet Header How the Internet works Special considerations for games Using a library vs writing your own Existing tools for Flash, C#, HTML Questions

122 Send complaints to: David