Devlog 4 - Client Inputs and Server Processing

So this is going to be a shorter post, but I just wanted to give a quick outline on how I'm handling client to server communication specfically for inputs.

First how do we handle client to server communication using UE5? It's actually quite simple on the outside Unreal let's us declare certain function on our PlayerController class that are designated to be RPC Calls

UFUNCTION(Server, Reliable)
void QueueInput(const FXYZInputMessage& InputMessage);
void QueueInput_Implementation(const FXYZInputMessage& InputMessage);

Assigning a UFUNCTION to be Server means that when this function is called on the client it will be executed on the remote server. Making it quite easy to send a payload of information from our client to the server on every input.

I created the payload as a Struct called XYZInputMessage and it looks as follows

struct FXYZInputMessage
        FString PlayerId;
        TArray<int32> SelectedActors;
        int32 XYZTargetActor;
        FVector TargetLocation;
        EXYZInputType InputType;
        bool bQueueInput;
        int32 AbilityIndex;
        int32 ActiveActorId;

• PlayerId is the UniqueNetId that a player controller has this will help us know if the player that sent it is really the player that sent it :)
• SelectedActors Let's us know which Units are to be handled in this current input you can learn more about that in my devlog about Blobs
• TargetActor is what actor is being targetted this could be a follow, attack, etc input
• TargetLocation what location is this input targetting this is used for many things like moving, attack moving, etc
• bQueueInput let's us know if this input should be added into the queue of a blob or if it should clear the blob queue and override the current action
• AbilityIndex let's us know what ability id is being told we are using
• ActiveActorId is the type of actor that the ability id corresponds for example if in starcraft I have marines and marauders selected and I pressed stim the marines would be the active actor id
• InputType is what kind of input are we telling the server it is there's many but ill give a few examples. MOVE, HOLD, STOP, FOLLOW, ATTACK_TARGET, ATTACK_MOVE, ABILITY

When the QueueInput function is executed on the remote server it then passes it along to the server's InputManager which is processed every tick InputManager->QueueInput(TickInput);

The InputManager every process goes through it's InputQueue and executes inputs that are valid

void Process(float DeltaTime)
{
    for(;InputQueueIndex < InputQueue.Num();InputQueueIndex++)
    {
        ExecuteInput(InputQueue[InputQueueIndex]);
    }
}

But what do these inputs turn into? Well every Input that a client does that the server needs to know is turned into an XYZAction in our not so pretty XYZActionFactory

The factory takes in an InputMessage and spits out one of the many actions

These actions are passed onto our blobs (group of units structure) which then processes the actions.

Here's a beautifully drawn diagram to show the flow

Thanks for reading!

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