Replication block - Revision history

Wormbo: more clarifications and details

2011-03-07T13:35:30Z

more clarifications and details

Eliot at 01:53, 3 July 2010

2010-07-03T01:53:32Z

00zX: /* Syntax */ - Added note on dynamic arrays

2010-04-20T21:35:28Z

‎Syntax: - Added note on dynamic arrays

Wormbo: Created page with 'The '''replication''' block specifies conditions for replicating variables and prior to Unreal Engine 3 also for functions. It contains one or more replication condit…'

2009-12-10T12:48:04Z

Created page with 'The '''replication''' block specifies conditions for replicating variables and prior to Unreal Engine 3 also for functions. It contains one or more replication condit…'

New page

The '''replication''' block specifies conditions for replicating [[variables]] and prior to [[Unreal Engine 3]] also for [[functions]]. It contains one or more replication conditions, each with one or more variable or function names to which the condition applies.

==Syntax==
The general syntax of the replication block looks as follows:
'''replication'''
'''{'''
''condition 1''
''condition 2''
...
'''}'''

Replication conditions in [[Unreal Engine 1]] and [[Unreal Engine 2|2]] have the following syntax:
['''un''']'''reliable if ('''''boolean expression''''')'''
''variable or function name'' [''',''' ...] ''';'''
The keyword '''reliable''' or '''unreliable''' only affects functions, but still must be specified for variables even though it doesn't make a difference there. Unreliably replicated [[function calls]] may be dropped due to bandwidth saturation, while reliably replicated function calls will be delayed in that case.

[[Unreal Engine 3]] uses simplified replication conditions because function replication is specified via [[Functions#Network modifiers|function modifiers]]:
'''if ('''''boolean expression''''')'''
''variable name'' [''',''' ...] ''';'''

Typically a replication condition tests the local value of the [[Role]] property, usually as <code>Role == ROLE_Authority</code> for server-to-client replication or <code>Role != ROLE_Authority</code> for client-to-server replication. For replicated functions this is usually the only condition.

In Unreal Engine 1 variables can be replicated from the server to all clients, but also from the client owning the actor to the server, similar to replicated function calls. That's why Unreal engine 1 replication conditions always check the Role. In Unreal Engine 2 and 3 variables can only be replicated from the server to clients, so technically the Role doesn't need to be checked at all. Still even Epic code contains Role checks for replicated variables in many classes.

For variable replication there are also other useful actor properties, such as bNetInitial and bNetOwner, which further narrow down when to replicate the variable and who to replicate it to.

==Exceptions==
For relatively obvious reasons, functions declared as ''static'', ''latent'' or ''iterator'' can't or shouldn't be replicated. Functions replicated to clients must be declared as ''simulated'' if you want them to be executable on ''ROLE_SimulatedProxy'' or ''ROLE_DumbProxy'' clients.

If a class is declared with the ''NativeReplication'' modifiers, the replication conditions in its replication block ignored for variables. Instead variable replication conditions are defined in native code. Function replication conditions are still specified in the replication block as usual. The reason these classes still contain replication conditions for variables is that UnrealScript coders should know when variables are actually replicated. The information may be inaccurate though, as the UT2004 [[UE2:Pickup (UT2004)|Pickup]] class shows. Its bOnlyReplicateHidden property turns off replication for all but the bHidden property.

Replicating variables declared as ''config'', ''globalconfig'' or ''localized'' may not have the desired effect as these variables may have different initial values on the server and the clients. The configured or localized values ''are'' the default values on the server and replication only kicks in if the values have changed.

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	For variable replication there are also other useful actor properties, such as bNetInitial and bNetOwner, which further narrow down when to replicate the variable and who to replicate it to.		For variable replication there are also other useful actor properties, such as bNetInitial and bNetOwner, which further narrow down when to replicate the variable and who to replicate it to.
		+
		+	Unlike any other data type in UnrealScript, [[Dynamic_array\|dynamic arrays]] have absolutely no support for replication. Attempting to replicate a dynamic array variable will have no effect on the remote instance of that variable. Attempting to use a dynamic array as parameter of a [[replicated function]] will result in the parameter being empty when the function is executed on the remote side. '''Explain Why''' can loose sync! it is possible to crosscheck dynamic arrays but it would come at a cost.

	==Exceptions==		==Exceptions==

@@ Line 25: / Line 25: @@
 For variable replication there are also other useful actor properties, such as bNetInitial and bNetOwner, which further narrow down when to replicate the variable and who to replicate it to.
-Unlike any other data type in UnrealScript, [[Dynamic_array|dynamic arrays]] have absolutely no support for replication. Attempting to replicate a dynamic array variable will have no effect on the remote instance of that variable. Attempting to use a dynamic array as parameter of a [[replicated function]] will result in the parameter being empty when the function is executed on the remote side. '''Explain Why''' can loose sync! it is possible to crosscheck dynamic arrays but it would come at a cost.
+Unlike any other data type in UnrealScript, [[dynamic arrays]] have absolutely no support for replication whatsoever. Attempting to replicate a dynamic array variable will have no effect on the remote instance of that variable. Attempting to use a dynamic array as parameter of a [[replicated function]] will result in the parameter being empty when the function is executed on the remote side. Similar restrictions apply to dynamic arrays within replicated struct values.
 ==Exceptions==
-For relatively obvious reasons, functions declared as ''static'', ''latent'' or ''iterator'' can't or shouldn't be replicated. Functions replicated to clients must be declared as ''simulated'' if you want them to be executable on ''ROLE_SimulatedProxy'' or ''ROLE_DumbProxy'' clients.
+For relatively obvious reasons, functions declared as ''static'', ''latent'' or ''iterator'' can't or shouldn't be replicated. Functions replicated to clients must be declared as ''simulated'' if you want them to be executable on ''ROLE_SimulatedProxy'' or ''ROLE_DumbProxy'' clients. Note that the UE3 [[Functions#Network modifiers|function modifiers]] ''client'' or ''demorecording'' already imply the ''simulated'' modifier, so you don't need to specify it again. The same goes for the ''native'' function modifier. Whether the similar [[DLLImport]] modifier implies ''simulated'' (or whether such functions support replication at all) is currently unknown, but then again you probably don't want to call such a function directly via replication.
-If a class is declared with the ''NativeReplication'' modifiers, the replication conditions in its replication block ignored for variables. Instead variable replication conditions are defined in native code. Function replication conditions are still specified in the replication block as usual. The reason these classes still contain replication conditions for variables is that UnrealScript coders should know when variables are actually replicated. The information may be inaccurate though, as the UT2004 [[UE2:Pickup (UT2004)|Pickup]] class shows. Its bOnlyReplicateHidden property turns off replication for all but the bHidden property.
+If a class is declared with the ''NativeReplication'' modifiers, the replication conditions in its replication block are ignored for variables. Instead variable replication conditions are defined in native code. Function replication conditions are still specified in the replication block (or in UE3 via function modifiers) as usual. The reason these classes still contain replication conditions for variables is that UnrealScript coders should know when variables are actually replicated. The information may be inaccurate though, as the UT2004 [[UE2:Pickup (UT2004)|Pickup]] class shows. Its bOnlyReplicateHidden property turns off replication for all but the bHidden property.
 Replicating variables declared as ''config'', ''globalconfig'' or ''localized'' may not have the desired effect as these variables may have different initial values on the server and the clients. The configured or localized values ''are'' the default values on the server and replication only kicks in if the values have changed.