Normally in UnityUnreal, if you wish to spawn a Prefab Actor at runtime, you would simply call GameObject.Instantiate “Spawn Actor From Class” in Blueprint, or UWorld::SpawnActor from C++, to make a new instance of it.
There are a couple of problems you run into when doing this in Cavrnus however.
The spawn object spawned isn’t synchronized for everyone, so only you your local client will see the new object.
Even if it was synchronized, every instance would share the same property paths as the base prefab, so they couldn’t behave individually.
Both of these problems are solved using the CavrnusFunctionLibrary API call SpawnObject.
What this does is it posts the object spawn to the journal and, in doing that, assigns it a new Property Path. Then when the object is Instantiated() instantiated it goes through all the PropertiesContainers and updates their property paths to reflect the unique journal identifier for the spawned instance.
Setting up a Prefab to be Spawnable
To make your prefab spawnable, you need only right-click on it, and then select Cavrnus → Make Selection Spawnable.
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What this does under-the-hood is it adds that prefab to the Cavrnus Spatial Connector’s Spawnable Objects list. It also gives it a uniqueId (generally the name of the prefab, but we modify it slightly for duplicate names).
This UniqueId to add it to the list of actor classes in the CavrnusSpatialConnector in your level, with a unique name as the key.
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This unique string key is what you will use to actually spawn the object. (Note that this means you can modify or change the prefab and, as long as the UniqueId key name doesn’t change, old journal operations will now spawn the new prefab.)
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Spawning your Prefab
Now, let’s write up a simple UI button script to spawn the object:
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As you can see, we’re simply passing in that UniqueId from above. The value we get back, meanwhile, is the Container Name of the new Instance. So, when the new prefab is spawned, the Cavrnus Properties Container at it’s root will use this Container Name.
Properties on Spawned Objects
Spawned object property names are handled in a very similar way to Avatar Instances.
Essentially what happens is the initial root Container Name is replaced with the new spawned instance ID. Then, every sub-object that starts with the root Container Name swaps out that part of the string for new new Id.
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| Code Block |
|---|
public void SpawnPrefab()
{
if (spaceConn == null)
return;
string instanceContainerName = spaceConn.SpawnObject("Cuby McCubeface");
spaceConn.PostBoolPropertyUpdate(instanceContainerName, "Visibility", true);
} |
Deleting Spawned Objects
When deleting a spawned object, you will need to access the Cavrnus Spawned Object Flag attached to it. This can be done with a simple GetComponent call. Once you have it, simply call DestroyObject on it.
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