Unreal Engine 4. New network model: PushModel

In the standard Unreal Engine network architecture, the server checks if the value of the replicated Actor class variable has changed, and in case of a difference, the value is synchronized between the server and the client. When the amount of data to sync is small, there are no particular performance issues.

However, a game can often consist of a huge set of Actors and variables that need to be replicated to one or more clients, and this can already become a problem area.

UE already provides features like: NetUpdateFrequency, NetCullDistanceSquared, etc. The main task of which is to eliminate from the general replication picture as many actors as possible who do not need to constantly synchronize data.

PushModel is, for now, an experimental feature that can allow developers to actively mark the need to synchronize a property, several macros are provided for this:

#define MARK_PROPERTY_DIRTY(Object, Property) 
#define MARK_PROPERTY_DIRTY_STATIC_ARRAY_INDEX(Object, RepIndex, ArrayIndex) 
#define MARK_PROPERTY_DIRTY_STATIC_ARRAY(Object, RepIndex, ArrayIndex) 

#define MARK_PROPERTY_DIRTY_FROM_NAME(ClassName, PropertyName, Object) 
#define MARK_PROPERTY_DIRTY_FROM_NAME_STATIC_ARRAY_INDEX(ClassName, PropertyName, ArrayIndex, Object) 
#define MARK_PROPERTY_DIRTY_FROM_NAME_STATIC_ARRAY(ClassName, PropertyName, ArrayIndex, Object) 
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

These macros set a specific variable to mark the need for synchronization, and the server, in turn, removes the need to constantly check for changes in value.

How to set up PushModel. First of all, in Build.cs, you need to add to exclude compilation problems

PublicDependencyModuleNames.AddRange(new string[]  {"NetCore"});
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Secondly, mark the necessary variables UPROPERTY (Replicated) or (ReplicatedUsing)

, GetLifetimeReplicatedProps, DOREPLIFETIME_WITH_PARAMS DOREPLIFETIME_WITH_PARAMS_FAST, DOREPLIFETIME DOREPLIFETIME_CONDITION, . :

void ASomeActor::GetLifetimeReplicatedProps(TArray< class FLifetimeProperty > & OutLifetimeProps) const
{
  Super::GetLifetimeReplicatedProps(OutLifetimeProps);
	FDoRepLifetimeParams SharedParams;
	SharedParams.bIsPushBased = true;
	SharedParams.Condition = COND_OwnerOnly;
	DOREPLIFETIME_WITH_PARAMS_FAST(ASomeActor, SomeVar, SharedParams);
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

FDoRepLifetimeParams 3 :

struct ENGINE_API FDoRepLifetimeParams
{
	/** Replication Condition. The property will only be replicated to connections where this condition is met. */
	ELifetimeCondition Condition = COND_None;
	/**  * RepNotify Condition. The property will only trigger a RepNotify if this condition is met, and has been  * properly set up to handle RepNotifies.  */
	ELifetimeRepNotifyCondition RepNotifyCondition = REPNOTIFY_OnChanged;
	/** Whether or not this property uses Push Model. See PushModel.h */
	bool bIsPushBased = false;
};
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

bIsPushBased , PushModel. , , . , :

MARK_PROPERTY_DIRTY_FROM_NAME(ASomeActor, SomeVar, this);
SomeVar = SomeValue;
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, .

PushModel , , .

Detailed usage examples can be found in the APlayerState class in the engine.

Thank you all for your attention and good time.