Question Preventing Self-Inflicted Damage in NPC Combat System

I'm facing an issue with my NPC combat system in Unity. I have NPC equipped with weapon as child object to their hand armatures. The NPCs have ragdoll setups, and the weapons have colliders for damage detection (OnTriggerEnter). However, I'm struggling to prevent self-inflicted damage when an NPC hits itself with its own weapon.

I've tried a few approaches like using Physics.IgnoreCollision, custom physics layers, and checking CompareTag on the weapon collider during the attack animation, but this means that other NPC will not be able to damage the NPC.

 

Sounds like you rolled a crit failure perhaps??

There's a bunch of ways, ranging from the outer layer like the physics ignore collision stuff, down to the internal structure of your data, the data depicting the damage, the damager, the damagee, etc.

One simple way is to put a field on the damage object that specifies the owner, and if you receive it you could check "Hey, this damage came from me, luckily I'm in a video game or else I would have chopped my arm off!" and decide to ignore it.

You could do this generally such as "player or NPC," but then individual NPCs won't be able to damage each other, even if they wanted.

You could do it at a faction level, such as Human, Alien or Protoss.. but then if you have two Protoss faction instances that want to go to war, they couldn't.

Finally could just do it as a check against your own identity (such as a with a simple very-transient identifier like that returned by .GetInstanceID()) and decide that way.

Which way you choose will be dependent on your game design.

 

Code (CSharp):

1.     void OnCollisionEnter(Collider other)
2.     {
3.         if (other.tag=="Sword")
4.         {
5.             if (other.transform.parent!=transform)
6.             {
7.                 Debug.Log("I was hit by somebody elses sword");
8.             }
9.             else
10.             {
11.                 Debug.Log("I just stabbed myself. oops..");
12.             }
13.         }
14.     }

 

For some reason 50% of the times when it collides with itself it will say "I just stabbed myself. oops.." and other 50% "I was hit by somebody elses sword", why?

 

Name the two swords differently and start printing their names to Debug.Log()

Just good old standard debugging!!

Time to start debugging! Here is how you can begin your exciting new debugging adventures:

You must find a way to get the information you need in order to reason about what the problem is.

Once you understand what the problem is, you may begin to reason about a solution to the problem.

What is often happening in these cases is one of the following:

- the code you think is executing is not actually executing at all
- the code is executing far EARLIER or LATER than you think
- the code is executing far LESS OFTEN than you think
- the code is executing far MORE OFTEN than you think
- the code is executing on another GameObject than you think it is
- you're getting an error or warning and you haven't noticed it in the console window

To help gain more insight into your problem, I recommend liberally sprinkling

Debug.Log()

statements through your code to display information in realtime.

Doing this should help you answer these types of questions:

- is this code even running? which parts are running? how often does it run? what order does it run in?
- what are the names of the GameObjects or Components involved?
- what are the values of the variables involved? Are they initialized? Are the values reasonable?
- are you meeting ALL the requirements to receive callbacks such as triggers / colliders (review the documentation)

Knowing this information will help you reason about the behavior you are seeing.

You can also supply a second argument to Debug.Log() and when you click the message, it will highlight the object in scene, such as

Debug.Log("Problem!",this);

If your problem would benefit from in-scene or in-game visualization, Debug.DrawRay() or Debug.DrawLine() can help you visualize things like rays (used in raycasting) or distances.

You can also call Debug.Break() to pause the Editor when certain interesting pieces of code run, and then study the scene manually, looking for all the parts, where they are, what scripts are on them, etc.

You can also call GameObject.CreatePrimitive() to emplace debug-marker-ish objects in the scene at runtime.

You could also just display various important quantities in UI Text elements to watch them change as you play the game.

Visit Google for how to see console output from builds. If you are running a mobile device you can also view the console output. Google for how on your particular mobile target, such as this answer for iOS: https://forum.unity.com/threads/how-to-capturing-device-logs-on-ios.529920/ or this answer for Android: https://forum.unity.com/threads/how-to-capturing-device-logs-on-android.528680/

If you are working in VR, it might be useful to make your on onscreen log output, or integrate one from the asset store, so you can see what is happening as you operate your software.

Another useful approach is to temporarily strip out everything besides what is necessary to prove your issue. This can simplify and isolate compounding effects of other items in your scene or prefab.

Here's an example of putting in a laser-focused Debug.Log() and how that can save you a TON of time wallowing around speculating what might be going wrong:

https://forum.unity.com/threads/coroutine-missing-hint-and-error.1103197/#post-7100494

"When in doubt, print it out!(tm)" - Kurt Dekker (and many others)

Note: the

print()

function is an alias for Debug.Log() provided by the MonoBehaviour class.

 

Okay I got it working with

Code (CSharp):

1. if (gameObject.name != other.gameObject.transform.root.name)
2. {
3.     Debug.Log("That isn't me");
4. }
5. else
6. {
7.      Debug.Log("That is me");
8. }

 

Instead of name, maybe use the Instance ID. Two NPC objects might have the same name and so they won't be able to fight each other.

 

Code (CSharp):

1. public void OnWeaponTriggerEnter(Collider other)
2. {
3.         if (gameObject.GetInstanceID() != (other.gameObject.transform.root).GetInstanceID())
4.         {
5.             Debug.Log("gameobject instance id: " + gameObject.GetInstanceID() + " gameobject name: " + gameObject.name);
6.             Debug.Log("root gameobject instance id: " + other.gameObject.transform.root.GetInstanceID() + " root gameobject name: " + other.gameObject.transform.root.name);
7.  
8.             Debug.Log("NPC has attacked something else");
9.         }
10.  
11.         else
12.         {
13.             Debug.Log("NPC has attacked itself");
14.         }
15. }

If I try to do that the name of the gameobject is the same, but the instanceID is different. This script is attached to the player and the function gets called on the weapon script that is attached to the weapon, so theoretically the root of the weapon is the same as the current gameobject but it's different instanceID for some reason, here is the weapon script aswell:

Code (CSharp):

1. private void OnTriggerEnter(Collider other)
2. {
3.      npcController.OnWeaponTriggerEnter(other);
4. }

 

You're checking "an GameObject's InstanceID == a transform's InstanceID" which won't be the same, since they are different objects. Every Object in Unity has different InstanceID.
More infos: Transform.root returns the root Transform, not the GameObject.

 

Oh oops, you are right. other.gameObject.transform.root.gameObject fixed it