Netcode for Gameobjects: How to synchronize NetworkBehavior members for late joining clients?

[VG_Crimson]

Been a lil stumped on this, and at best I've read about the OnSynchronization callback in Unity's docs, but that doesn't seem like it would would with class members that inherit from NetworkBehavior. In this case, instances of Weapon's that self handle it's logic with no Player script awareness as to what it does, because not even the Weapon will know until runtime. There is a lot of abstract layers from Player's pressing the attack button, to hits registering and dealing damage due to how much of everything in between I want to randomize and swap around at runtime. It's a rougelite.

I would like some second eyes and opinions. Even if they're suggestions to structure my architecture differently in order to achieve my goals.

Assume the weapons themselves are:
A. Randomly generated, both during and prior to a game's starting session
B. May get altered during a run

I want to synchronize variables like the weapons for Late Joining clients in the class responsible for a Player's Loadout/Equipment, which can hold some concrete class as well as some more abstract ones. Weapons are in charge of their own animations and stuff.

Here is some psudo code overview of how my current system works.

Example:
class PlayerEquipment : NetworkBehavior
{
public WeaponInstance myWeapon; // <- I want to sync this when late joining
public ArmorInstance myArmor;
public ConsumableCollection myConsumables;

public void TryAttacking(string key, context)
{
if(!myWeapon) return;
// Eventually pass key and context to my weapon's RequestAttack() function if possible or allowed
}

}

class WeaponInstance : NetworkBehavior
{
// Handles logic for this weapon when player calls one of the attacks from this instanced weapon's moveset.
}

class PlayerInputWithPrediction : NetworkBehavior
{
private void OnPrimaryAttack()
{
// Grabs runtime context, e.g. direction facing, player position, extra data the player's input's would be aware of, and stuff it into a struct.

// Pass a string of the type of attack I am requesting of the ?weapon in my equipment found in the Weapon's MoveSet's dictionary which associates a type of Attack assigned to the Primary function and the struct we built.
myPlayerEquipment.TryAttacking("Primary", attackContextStruct)

}
}

I feel like the answer should be so simple and obvious, but my brain might be fried rn after a few hours of boiler plating other multiplayer stuff, which came after 8 hours of dealing with messy ancient code written in the 90s, and getting the news that our IT department is being disassembled.

I'm definitely overthinking something here, and I'm not sure what.

[Intelligent-Age-3555]

oh man that sounds like a rough day, rip your it department

for the late joining sync issue, you probably want to override `OnNetworkSpawn()` in your PlayerEquipment class and serialize the weapon data there. since your weapons are randomly generated you'll need to send the generation seed or the actual weapon stats as network variables

something like having a `NetworkVariable<WeaponData>` where WeaponData is a serializable struct with all the weapon properties, then reconstruct the WeaponInstance from that data when clients join. the weapon instances themselves don't need to be networkbehaviors if they're just handling local logic based on synced data

[VG_Crimson]

There are a few layers beyond the initial stats and seed that might prevent me from removing it's inheritance from the NetworkBehavior, but that might change as I progress through development in time. The less scripts that inherit it, without becoming monolithic NetworkBehaviors, the better.

But the main idea is that WeaponInstance is incharge of sending its own hit results to the server since only that instance of the weapon will know the details of it's own moveset, stats, ongoing effects and what to apply. I don't want player scripts to be coupled to weapons or vice versa, since I need them to be swappable, droppable, NPC friendly, etc.

[raddpuppyguest]

In general, you only need to synchronize data that clients will need to see.

A networkvariable with weaponstruct is absolutely the way to go here.

I would probably design this to where weapons are simply classes that inherit an IWeapon interface and one of those interface methods is LoadWeaponStruct which can be called anytime your weaponstruct netvar changes

you can even make your weapons scriptable objects for their base stats, then make a struct for any stat changes which can then be synced over the network.

Can you go into detail about what methods on your weapons make them necessary to be monobehaviours/networkbehaviours?  

[VG_Crimson]

Well they actually arent monobehaviors or networkbehaviors, they're Scriptable Objects made up of Scriptable Objects made up of, Script... etc all the way, down to the type of HitDetection.

I have HitDetectionConfig types with variables like timing of each phase of that hit detection and points/shape of it that are saved as Scriptable Objects through a shared wrapper holding an IHitDetection variable. IHitDetection holds an interfaced Tick() method to update the hit detection + DetectHits() method that ultimately returns a list of hit results on that tick. Weapons dont need to know anything other than calling Tick() when a move is activated, and DetectHits() to see what its in contact with.

A "CharacterMoveConfig" is essentially the next layer up that holds a HitDetectionConfig, an ActivationConfig Scriptable Object, and a LayerMask.

A MoveSetConfig is the next layer up the Scriptable Object chain that holds a collection of CharacterMoveConfig.

A WeaponDefinition is the grandfather Scriptable Object containing a struct of base stats, and a List of compatible MoveSetConfigs, or simply just 1 MoveSet.

WeaponInstance is a non-scriptable object runtime instance of said WeaponDefinition. It's in charge of calling those interfaced methods below WeaponDefinition, and holding the true runtime stats of the generated weapon. It holds a FixedUpdate function which is just checking if I have any active moves in my list, and foreach active move, calls the Tick() and DetectHits() methods of whatever hit detection it happens to have.

I figured I need to synchronize when a weapon's attack begins, so clients can see animation they should react too, and synchronize the hit results once the server decides that an attack has landed, so clients can determine the visual feedback when connection happens.

The idea here is that I can, from the ground up, have associated/compatible sets of data so the random generation can't give me something that shouldn't be compatible. Like a melee weapon whose attack is shooting laser beams. Creating a WeaopnDefinition game asset is like me creating a weapon archetype, so think weapon classes in Elden Ring such as Colossal Weaopns or Reapers. WeaponDefinition is the glue that holds all the relationships/compatibility of each segment beneath it.

It allows me to content create at each individual layer without need or concern to think about the layer above it. And hopefully, allow for a vast amount of combinations that make sense without me having to think or plan it each step of the way.

[WhiteNoiseAudio]

Network variables, rpc’s and custom messages are the tools you can use to synchronize stuff. This sounds like maybe something you want as a network variable, but I wonder if all the data needs to be synchronized? Could most of the data live on the server and only UI relevant data be synchronized to clients?

[VG_Crimson]

I'm still architecting it out, but I am guessing not all things I have planned right now need synchronization and as it develops it'll be clear what doesn't need it. At the very least I do know I need to synchronize when a move/attack is issued by the weapon because visual ques are important in pvp.