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.NET Platform SDK

This is the documentation and reference for the Photon Client Library for .NET, Unity and Windows Phone.


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Photon is a development framework to build real-time multiplayer games and applications for various platforms. It consists of a Server SDK and Client SDKs for several platforms. Photon provides a low-latency communication-layer based on UDP (or alternatively TCP). It enables reliable and unreliable transfer of data in "commands". On top of this, an operation- and event-framework is established to ease development of your own games.

Each game is different, so we developed several "server applications" which provide a basic logic and included them in the server SDK as example and code base.

• The "Lite" Application offers the basic operations that we felt useful for most room-based multiplayer games. We included its operations and events are part of the client API.

• The "LoadBalancing" Application extends the "Lite" Application and allows you to run multiple servers for your game. A master server coordinates the games creation and joining. There is a special API in the SDK that makes use of this application.

• The "MMO" Application.

Photon Cloud is a hosted service for your Photon games. To use it, register here and use the LoadBalancing API and demos to start your development.

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Photon Workflow

To get an impression of how to work on the client, we will use the server's Lite logic. This application defines rooms which are created when users try to join them. Each user in a room becomes an actor with her own number.

A simplified workflow looks like this:

  • create a LitePeer instance
  • from now on: regularly call Service to get events and send commands (e.g. ten times a second)
  • call Connect to connect the server
  • wait until the library calls OnStatusChanged
  • the returned status int should equal StatusCode.Connect
  • call OpJoin to get into a game
  • wait until the library calls OnOperationResponse with opCode: LiteOpCode.Join
  • send data in the game by calling OpRaiseEvent
  • receive events in OnEvent
  • The Lite Application defines several useful events for common situations: Someone joins or leaves the room.
  • InLite, events created by calling OpRaiseEvent will be received by others in the same room in this method.
  • when you are done: call LitePeer.OpLeave to quit/leave the game
  • wait for "leave" return in OnOperationResponse with opCode: LiteOpCode.Leave
  • disconnect with Disconnect
  • check "disconnect" return in OnStatusChanged with statusCode: StatusCode.Disconnect Combined with the server's Lite application, this simple workflow would allow you to use rooms and send your game's events. The methods used could be broken down into three layers:
  • Low Level: Service, Connect, Disconnect and the OnStatusChanged are directly referring to the connection to the server. This level works with UDP/TCP packets which transport commands (which in turn carry your operations). It keeps your connection alive and organizes your RPC calls and events into packages.
  • Logic Level: Operations, results and events make up the logical level in Photon. Any operation defined on the server (think RPC call) and can have a result. Events are incoming from the server and update the client with some data.
  • Application Level: Made up by a specific application and its features. In this case we use the operations and logic of the Lite application. In this specific case, we have rooms and actors and more.

The LitePeer is matching the server side implementation and wraps it up for you. You don't have to manage the low level communication in most cases. However, it makes sense to know that everything that goes from client to server (and the other way round) is put into "commands". Internally, commands are also used to establish and keep the connection between client and server alive (without carrying additional data).

All methods that are operations (RPC calls) are prefixed with "Op" to tell them apart from anything else. Other server side applications (like MMO or your own) will define different operations. These will have different parameters and return values. These operations are not part of the client library but can be implemented by calling OpCustom. The interface IPhotonPeerListener must be implemented for callbacks. They are:

  • OnStatusChanged is for peer state-changes (connect, disconnect, errors, compare with StatusCode Enumeration)
  • OnOperationResponse is the callback for operations (join, leave, etc.)
  • OnEvent as callback for events coming in
  • DebugReturn as callback to debug output (less frequently used by release builds) The following properties in PhotonPeer are of special interest:
  • TimePingInterval sets the time between ping-operations
  • RoundTripTime of reliable operations to the server and back
  • RoundTripTimeVariance shows the variability of the roundtrip time
  • ServerTimeInMilliSeconds is the continuously approximated server's time

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Operation is our term for remote procedure calls (RPC) on Photon. This in turn can be described as methods that are implemented on the server-side and called by clients. As any method, they have parameters and return values. The Photon development framework takes care of getting your RPC calls from clients to server and results back. Server-side, operations are part of an application running on top of Photon. The default application provided by Exit Games is called "Lite Application" or simply Lite. The LitePeer class extends the PhotonPeer by methods for each of the Lite Operations.

Examples for Lite Operations are "join" and "raise event". On the client side, they can be found in the LitePeer class as methods: OpJoin and OpRaiseEvent. They can be used right away with the default implementation of Photon and the Lite Application.

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Custom Operations

Photon is extendable with features that are specific to your game. You could persist world states or double check information from the clients. Any operation that is not in Lite or the MMO application logic is called Custom Operation. Creating those is primarily a server-side task, of course, but the clients have to use new functions / operations of the server.

So Operations are methods that can be called from the client side. They can have any number of parameters and any name. To lower traffic, we assign byte-codes for every operation and each parameter. The definition is done server side. Each Operation has its own, unique number to identify it, known as the operation code (opCode). An operation class defines the expected parameters and assigns a parameter code for each. With this definition, the client side only has to fill in the values and let the server know the opCode of the Operation. Photon uses Dictionaries to aggregate parameters for operation requests, responses and events. Use OpCustom to call any operation, providing the parameters in a Dictionary. Client side, opCode and parameter-codes are currently of type byte (to minimize overhead). They need to match the definition of the server side to successfully call your operation.

Recommended for further reading:

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Unlike operations, events are "messages" that are rarely triggered by the client that receives them. Events come from outside: the server or other clients. They are created as side effect of operations (e.g. when you join a room) or raised as main purpose of the operation Raise Event. Most events carry some form of data but in rare cases the type of event itself is the message. Events are (once more) Dictionaries with arbitrary content. In the "top-level" of an event, bytes are used as keys for values. The values can be of any serializable type. The Lite Application, e.g., uses a Hashtable for custom event content in its operation RaiseEvent.

Recommended for further reading:

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Fragmentation And Channels


Bigger data chunks of data won't fit into a single package, so they are fragmented and reassembled automatically. Depending on the data size, a single operation or event can be made up of multiple packages.

Be aware that this might stall other commands. Call Service or SendOutgoingCommands more often than absolutely necessary. You should check that PhotonPeer.QueuedOutgoingCommands is becoming zero regularly to make sure everything gets out. You can also check the debug output for "UDP package is full", which can happen from time to time but should not happen permanently. Maximum Transfer Unit

The maximum size for any UDP package can be configured by setting PhotonPeer.MaximumTransferUnit Property. By default, this is 1200 bytes. Some routers will fragment even this UDP package size. If you don't need bigger sizes, go for 512 bytes per package, which is more overhead per command but potentially safer. This setting is ignored by TCP connections, which negotiate their MTU internally.

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The sequencing of the protocol makes sure that any receiving client will Dispatch your actions in the order you sent them. Unreliable data is considered replaceable and can be lost. Reliable events and operations will be repeated several times if needed but they will all be dispatched in order without gaps. Unreliable actions are also related to the last reliable action and not dispatched before that reliable data was dispatched first. This can be useful, if the events are related to each other.

Example: Your FPS sends out unreliable movement updates and reliable chat messages. A lost package with movement updates would be left out as the next movement update is coming fast. On the receiving end, this would maybe show as a small jump. If a package with a chat message is lost, this is repeated and would introduce lag, even to all movement updates after the message was created. In this case, the data is unrelated and should be put into different channels.

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The .NET clients and server are now supporting "channels". This allows you to separate information into multiple channels, each being sequenced independently. This means, that Events of one channel will not be stalled because events of another channel are not available. By default an PhotonPeer has two channels and channel zero is the default to send operations. The operations join and leave are always sent in channel zero (for simplicity). There is a "background" channel 255 used internally for connect and disconnect messages. This is ignored for the channel count. Channels are prioritized: the lowest channel number is put into a UDP package first. Data in a higher channel might be sent later when a UDP package is already full.

Example: The chat messages can now be sent in channel one, while movement is sent in channel zero. They are not related and if a chat message is delayed, it will no longer affect movement in channel zero. Also, channel zero has higher priority and is more likely to be sent (in case packages get filled up).

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Using TCP

A PhotonPeer could be instanced with TCP as underlying protocol if necessary. This is not best practice but some platforms don't support UDP sockets. This is why Silverlight (e.g.) uses TCP in all cases. The Photon Client API is the same for both protocols but there are some differences in what goes on under the hood. Everything sent over TCP is always reliable, even if you call your operations as unreliable! If you use only TCP clients simply send any operation unreliable. It saves some work (and traffic) in the underlying protocols. If you have TCP and UDP clients anything you send between the TCP clients will always be transferred reliable. But as you communicate with some clients that use UDP these will get your events reliable or unreliable.

Example: A Silverlight client might send unreliable movement updates in channel # 1. This will be sent via TCP, which makes it reliable. Photon however also has connections with UDP clients (like a 3D downloadable game client). It will use your reliable / unreliable settings to forward your movement updates accordingly.

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Network Simulation

During development, most tests will be done in a local network. Once released, the clients will communicate through the internet, which has a higher delay per message and in some cases even drops messages entirely. To prepare a game for real-life conditions, the Photon client libraries let you simulate some effects of internet-communication: lag, jitter and packet loss.

  • Lag / Latency: a more or less constant delay of messages between client and server. Either direction can be affected in a different way but usually the values are close to another. Affects the roundtrip time.
  • Jitter: Is randomizes the Lag in the simulation. This affects the variance of the roundtrip time. Udp packages can get out of order this way, which also is simulated. The new lag will be: Lag + [-JitterValue..+JitterValue]. This keeps the mean Lag at the setting and some packages are actually faster than the Lag value implies.
  • Packet Loss: UPD packages can become lost. In the Photon protocol, commands that are flagged as reliable will be repeated while other commands (operations) might get lost this way.

The lag simulation is running in its own Thread which tries to meet delays defined in the settings. In most cases, they can be met but actual delays will have a variance of up to +/- 20ms.

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Using Network Simulation

By default, Network Simulation is turned off. It can be turned on by setting PhotonPeer.IsSimulationEnabled and the settings are aggregated into a NetworkSimulationSet, also accessible by the peer class (e.g. the LitePeer). Code Sample:

//Activate / Deactivate:
this.peer.IsSimulationEnabled = true;
//Raise Incoming Lag:
this.peer.NetworkSimulationSettings.IncomingLag = 300; //default is 100ms
//add 10% of outgoing loss:
this.peer.NetworkSimulationSettings.OutgoingLossPercentage = 10; //default is 1
//this property counts the actual simulated loss:

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Serializable Datatypes

Starting with Photon Server SDK 1.8.0 and .NET SDK 5.6.0, the set of serializable datatypes is changed. The ArrayList was removed but aside from Arrays and Hashtables every serializable type can also be sent as array (e.g. String[], Float[]). Only one-dimensional arrays are supported currently.

Photon 1.8.0 and higher

  • String / string
  • Boolean / bool
  • Byte / byte (unsigned! can be cast to SByte / sbyte to be eqivalent to Java's byte)
  • Int16 / short (signed)
  • Int32 / int (signed)
  • Int64 / long
  • Single / float
  • Double / double
  • Array (of the types above, with a max number of Short.MaxValue enties).
  • Hashtable (not available as array)

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The Photon Server

The Photon Server is the central hub for communication for all your clients. It is a service that can be run on any Windows machine, handling the UDP and TCP connections of clients and hosting a .NET runtime layer with your own business logic, called application. The Photon Server SDK includes several applications in source and pre-built. You can run them out of the box or develop your own server logic. Get the Photon Server SDK here

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Lite Application

The Lite Application is the example application for room-based games on Photon and (hopefully) a flexible basis for your own games. It offers rooms, joining and leaving them, sending events to the other players in a room and handles properties. The Lite Application is tightly integrated with the client libraries and used as example throughout most documentation.

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Properties On Photon

The Lite Application implements a general purpose mechanism to set and fetch key/value pairs on the server side (in memory). They are associated to a room/game or a player within a room and can be fetched or updated by anyone in that game. Each entry in the properties Hashtable is considered a separate property and can be overwritten independently. The value of a property can be of any serializable datatype. The keys must be either of type string or byte. Bytes are preferred, as they mean the less overhead. To avoid confusion, don't mix string and byte as key-types. Mixed types of keys, require separate requests to fetch them. Property broadcasting and events Property changes in a game can be "broadcasted", which triggers events for the other players to update them. The player who changed the property does not get the update (again). Any change that uses the broadcast option will trigger a property update event. This event carries the changed properties (only), which changed the properties and where the properties belong to. Your clients need to "merge" the changes (if properties are cached at all). Properties can be set by these methods:

  • LitePeer.OpSetPropertiesOfActor Method sets a player's properties
  • LitePeer.OpSetPropertiesOfGame Method sets a game's properties
  • LitePeer.OpJoin Method also allows you to set properties if the game did not exist yet

And fetched with these methods:

  • OpGetPropertiesOfActor
  • OpGetPropertiesOfGame

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Broadcast Events

Any change that uses the broadcast option will trigger a property update event LiteEventCode.PropertiesChanged. This event carries the properties as value of key LiteEventKey.Properties. Additionally, there is information about who changed the properties in key LiteEventKey.ActorNr. The key LiteEventKey.TargetActorNr will only be available if the property-set belongs to a certain player. If it's not present, the properties are game-properties.

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The current Lite Application is not able to delete properties and does not support wildcard characters in string keys to fetch properties. Other types of keys could be used but to keep things simple, we decided against adding those. If needed, we would help you with the implementation. The property handling is likely to be updated and extended in the future.

Recommended for further reading:

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.NET Platforms

Photon For Unity3D

This chapter addresses differences between the .NET SDK and the one for Unity3D. If you don't use Unity3D, skip this chapter.

  1. Supported versions of Unity:
    a) Currently supported and tested Unity platforms are Standalone and Web (both Windows and MacOS) and iOS. The export to PS3, Wii and Android are not tested by us currently but should be working as well.
    b) Photon works fine with Unity Standard, with Unity Pro. Export to mobile devices requires the respective mobile "Pro" license to make use of .NET sockets.
  2. Unity 3 and policy file requests Starting with Unity 3.0, web players will require a policy file to connect to a different URL than their originating server. Photon supports this feature out of the box. By default the server opens the a port for policy file requests (TCP port 843) and maps it to the "Policy Application". We included source for this but in general it should be fine to just use deploy the binaries.
  3. How to add Photon to your Unity project:
    a) To add the Photon .dll from the SDK to a Unity project, just copy it somewhere in the assets-folder of the project and make sure that there are no duplicates (pay attention to old versions with different filenames).
    b) Make sure to have the following line of code somewhere in your scripts, so the game runs even when in background: Application.runInBackground = true; //without this Photon will loose connection if not focussed
    c) For the iOS builds, you should set the "iPhone Stripping Level" to "Strip Bytecode" (Edit->Project Settings->Player). Also, use the ".NET 2.0 subset". If your project runs fine in IDE and you get an error message when building it for device, please check this option.
    d) Make sure to change the server address used in the client, as "localhost:5055" won't work on device.

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