Unity Server GameObject destruction - unity3d

Question

I have a 2D game made in Unity in which I want the characters to be able to shoot bullets and when a bullet hits a player to push him back destroying the bullet. Due to server not syncing perfectly there are some cases in which the bullet is destroyed locally, but not on all clients so I want to make it a [Command] to destroy it on server and on all clients too.
The code for local looks like this:
void OnTriggerEnter2D(Collider2D col)
{
if (col.gameObject.tag == "bullet")
{
Explode (Mathf.Sign (col.attachedRigidbody.velocity.x));
Destroy(col.gameObject);
}
}
And I tried to make it for multiplayer like this
[Command]
void CmdOnTriggerEnter2D(Collider2D col)
{
if (col.gameObject.tag == "bullet")
{
Explode (Mathf.Sign (col.attachedRigidbody.velocity.x));
Network.Destroy(col.gameObject);
}
}
But it doesn't work.. it tells me that
CmdOnTriggerEnter2D parameter [col] is of the type [Collider2D] which is a Component. You cannot pass a Component to a remote call. Try passing data from within the component.
I understand that I should use another parameter, but how..? How can I do this function to work for my server?

Answer 1

As your output says you can not pass the Collider component reference as parameter since the Network does not know, where this reference belongs to on other instances.
In the Unity Documentation for Command you can find which values are allowed as parameter:
The allowed argument types are;
Basic type (byte, int, float, string, UInt64, etc)
Built-in Unity math type (Vector3, Quaternion, etc),
Arrays of basic types
Structs containing allowable types
NetworkIdentity
NetworkInstanceId
NetworkHash128
GameObject with a NetworkIdentity component attached.
=> Note especially the most bottom element in the list:
You can simply pass in the col.gameObject as long as it has a NetworkIdentity component on it!
Than I would make the check if the Tag Matches already before stressing the bandwidth of the networking. Meaning: Do the tab check local and only call the Command with the valid GameObject reference.
So your code should than look like
//local
void OnTriggerEnter2D(Collider col)
{
if (col.gameObject.tag != "bullet") return;
CmdOnTriggerEnter2D(col.gameObject);
}
// This is executed only on the server
[Command]
void CmdOnTriggerEnter2D(GameObject col)
{
// Depending on what Explode does you might want to pass it pack to all clients as well
// Since currently this will only happen on the server itself!
Explode (Mathf.Sign (col.attachedRigidbody.velocity.x));
Network.Destroy(col);
}
Requirement as said before is that you bullet object has a NetworkIdentity component but I assume this is already the case if this is a Network spawned prefab as I guess.
Note
As I mentioned in a comment I also guess Explode is something that should probably happen on all clients instead of only on the server. In this case you can do the following
//local
void OnTriggerEnter2D(Collider col)
{
if (col.gameObject.tag != "bullet") return;
// Already get the value needed for the Explode method
var value= Mathf.Sign (col.attachedRigidbody.velocity.x)
// Also pass the value so we can provide it to all clients later
CmdOnTriggerEnter2D(col.gameObject, value);
}
// This is executed only on the server
[Command]
void CmdOnTriggerEnter2D(GameObject col, float value)
{
// Tell all clients to Explode using the passed value
RpcExplode(value);
Network.Destroy(col);
}
// This is called by the server but executed by ALL clients
[ClientRpc]
void RpcExplode(float value)
{
Explode (value);
}
As I don't know what you Explode needs to work: Be careful with destroying the bullet object if it is needed to execute Explode ;)