[AI SCRIPTING] Panda BT: Behaviour Tree scripting

I've check your project, and indeed the BT scripts are ticked in the Editor. Some of your scripts are ticked on LateUpdate, which is apparently also called in the Editor. That's not specified in the [ExecuteInEditMode] documentation, only Update is mentioned there. I will fix this by also placing a tick guard in LateUpdate, as well as in FixedUpdate (just in case).

I understand you want to reuse code, that's a good thing (less is more). But how do you reuse a [task] that access Task.current.Succeed() or Fail(). Since Task.current is only available within BT script context, it makes the method useless when used in isolation.

If there are code to share between the BT scripts and another system, I would instead place this shared code inside a library, then both the [task] methods and the other system would make calls to this same library.

 

I skip all Task.current when it's not called from panda. It's not super elegant but it's clean enough and it works in the context of input loop calling functions.
I could do libraries yes but then I need to think harder than just skipping what is null, and thinking hard I don't like doing.

 

Note that Task.current is the same for MoveTowardsTarget and RealtimeWait. RealtimeWait calls Task.current.Succeed() after 0.1 seconds. Therefore, MoveTowardsTarget will succeeds after 0.1 seconds even if the agent did not reach the target. When MoveTowardsTarget succeeds, everything is done and the top sequence succeeds as well.

I'm not sure why you have the RealtimeWait within the MoveTowardsTarget task. Is it to somehow slow down the movement of the agent? What do you want to achieve?

 

So Wait/RealtimeWait will cause the method that they are located it to succeed? That explains it. Thanks for clearing it up. I had placed it inside the method because I was trying to cut down on the clutter in my behavior tree, but it look's like I won't be able to use it.

 

When trying Panda, I saw that it generated some garbage, so I've just bought the pro version in order to fix it.

First, there's some garbage generated in order to display the debug information, here is an example:

Code (CSharp):

1. public void Wait(float duration)
2. {
3.     [...]
4.  
5.     if (Task.isInspected)
6.     {
7.         task.debugInfo = string.Format("t-{0:0.000}", tta);     // Generates garbage
8.     }
9.  
10.     [...]
11. }
12.  

Unfortunately I cannot share my way of fixing it as I'm using a quite extensive replacement of the StringBuilder class in order to have concatenations and numeric to string transformation garbage-free.
But, in that particular case, it is probably possible to use a simpler version as it always has the same length.


Now the serious things, there's garbage generated in 3 cases:
- executing a task with a parameter and a return value
- executing a task that is a property
- executing a task that is a field

Here is the fix for the property:

Code (CSharp):

1. static bool Bind( BTTask task, TaskImplementation implementation)
2. {
3.     [...]
4.  
5.     if (property != null)
6.     {
7.         System.Func<bool> TheActionToExecute = (System.Func<bool>)System.Delegate.CreateDelegate(typeof(System.Func<bool>), taskImplementer, property.GetGetMethod(true));
8.         taskAction = () => Task.current.Complete(TheActionToExecute());
9.  
10. //        taskAction = () => Task.current.Complete((bool)property.GetValue(taskImplementer, null));
11.     }
12.  
13.     [...]
14. }
15.  

I also have a fix for the field, but unfortunately it cannot work for mobiles as it involves generating methods at runtime.
Anyway, it's just a matter of transforming the fields into properties, which is possible in most cases.


For the method problem, it's the same solution than for the property (after all, a property is a method), but it's more tricky because the signature of the method is not fixed.
So, it takes some efforts in order to cast the method correctly.
For now I have just done it for the basic methods, which takes only one parameter of type 'int', 'float' or 'string', and it works, here is the fix:

Code (CSharp):

1. static bool Bind( BTTask task, TaskImplementation implementation)
2. {
3.     [...]
4.  
5.     if (method.ReturnType == typeof(bool))
6.     {
7.         if (parameters.Length > 0)
8.         {
9.             if ((1 == parameters.Length) && (typeof(int) == parameters[0].GetType()))
10.             {
11.                 System.Func<int, bool> TheActionToExecute = (System.Func<int, bool>)System.Delegate.CreateDelegate(typeof(System.Func<int, bool>), taskImplementer, method);
12.                 taskAction = () => Task.current.Complete(TheActionToExecute((int)parameters[0]));
13.             }
14.             else if ((1 == parameters.Length) && (typeof(float) == parameters[0].GetType()))
15.             {
16.                 System.Func<float, bool> TheActionToExecute = (System.Func<float, bool>)System.Delegate.CreateDelegate(typeof(System.Func<float, bool>), taskImplementer, method);
17.                 taskAction = () => Task.current.Complete(TheActionToExecute((float)parameters[0]));
18.             }
19.             else if ((1 == parameters.Length) && (typeof(string) == parameters[0].GetType()))
20.             {
21.                 System.Func<string, bool> TheActionToExecute = (System.Func<string, bool>)System.Delegate.CreateDelegate(typeof(System.Func<string, bool>), taskImplementer, method);
22.                 taskAction = () => Task.current.Complete(TheActionToExecute((string)parameters[0]));
23.             }
24.             else
25.             {
26.                 taskAction = () => Task.current.Complete((bool)method.Invoke(taskImplementer, parameters));
27.             }
28.         }
29.     }
30.  
31.     [...]
32. }
33.  

And to finish with, I'd like to say that you did a good job with this asset.
I needed a BT that could access my own data and with the code source so that I could optimize it if necessary.
And it's very easy to enter in your code (I've fixed these issues in less than 3 hours, including reading the documentation and playing with the examples).

I still have a few questions:
- is it possible to run PandaBT on several threads simultaneously?
- how does it scale with a lot of nodes (I saw in the profiler that there are a lot of nested calls)?
- how are the performances with a lot of BT?

 

OK, after a small battle, C# lost and I finally managed to have garbage-free methods, whatever the parameters (well, not exactly, it works up to 9 parameters, but it's easy to improve it).

The idea was to transform your 'parameters' (of type object[]) into a typed list of parameters.
As I'm used to use generics everywhere, I used them again, here is the result:

Code (CSharp):

1. static bool Bind( BTTask task, TaskImplementation implementation)
2. {
3.     [...]
4.  
5.     if (method.ReturnType == typeof(bool))
6.     {
7.         taskAction = GetTaskAction(taskImplementer, method, parameters);
8.     }
9.  
10.     [...]
11. }
12.  
13. public static System.Action GetTaskAction(object taskImplementer, MethodInfo method, object[] parameters)
14. {
15.     if (0 == parameters.Length)         // Basic case
16.         return () => Task.current.Complete((System.Delegate.CreateDelegate(typeof(System.Func<bool>), taskImplementer, method) as System.Func<bool>)());
17.     else if (parameters.Length > 9)     // Unsupported cases
18.         return () => Task.current.Complete((bool)method.Invoke(taskImplementer, parameters));
19.  
20.     // Create the parameters arrays
21.     System.Type[] AllTypes = new System.Type[parameters.Length];
22.     object[] AllParameters = new object[parameters.Length + 2];
23.     AllParameters[0] = taskImplementer;
24.     AllParameters[1] = method;
25.     for (int i=0; i<AllTypes.Length; i++)
26.     {
27.         AllTypes[i] = parameters[i].GetType();
28.         AllParameters[i+2] = parameters[i];
29.     }
30.  
31.     // Find the correct generic method, build it and call it
32.     MethodInfo[] AllMethods = typeof(BTRuntimeBuilder).GetMethods(BindingFlags.NonPublic | BindingFlags.Static);
33.     for (int i=0; i<AllMethods.Length; i++)
34.     {
35.         MethodInfo CurrentMethod = AllMethods[i];
36.         if (!CurrentMethod.IsGenericMethod)
37.             continue;
38.  
39.         if ("GetTaskAction" != CurrentMethod.Name)
40.             continue;
41.  
42.         ParameterInfo[] ParametersOfCurrentMethod = CurrentMethod.GetParameters();
43.         if (AllParameters.Length != ParametersOfCurrentMethod.Length)
44.             continue;
45.  
46.         // We found the correct generic method, we can now build it
47.         MethodInfo TheGenericMethod = CurrentMethod.MakeGenericMethod(AllTypes);
48.  
49.         // Now we can call the generic method that will get the action task
50.         return (System.Action)TheGenericMethod.Invoke(null, AllParameters);
51.     }
52.  
53.     // Should never happen
54.     UnityEngine.Debug.LogError("Impossible to get the action task for '" + method.Name + "'");
55.     return null;
56. }
57.  
58. // Adds the missing declaration in this old version of Mono
59. public delegate Tret Func<T1, T2, T3, T4, T5, Tret>(T1 arg1,  T2 arg2, T3 arg3, T4 arg4, T5 arg5);
60. public delegate Tret Func<T1, T2, T3, T4, T5, T6, Tret>(T1 arg1,  T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6);
61. public delegate Tret Func<T1, T2, T3, T4, T5, T6, T7, Tret>(T1 arg1,  T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7);
62. public delegate Tret Func<T1, T2, T3, T4, T5, T6, T7, T8, Tret>(T1 arg1,  T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8);
63. public delegate Tret Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, Tret>(T1 arg1,  T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9);
64.  
65. // It's best to generate these methods automatically as they are all the same except for the number of parameters
66. private static System.Action GetTaskAction<T1>(object taskImplementer, MethodInfo method, T1 Param1)
67. {
68.     return () => Task.current.Complete(((System.Func<T1, bool>)(System.Func<T1, bool>)System.Delegate.CreateDelegate(typeof(System.Func<T1, bool>), taskImplementer, method))(Param1));
69. }
70.  
71. private static System.Action GetTaskAction<T1, T2>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2)
72. {
73.     return () => Task.current.Complete(((System.Func<T1, T2, bool>)(System.Func<T1, T2, bool>)System.Delegate.CreateDelegate(typeof(System.Func<T1, T2, bool>), taskImplementer, method))(Param1, Param2));
74. }
75.  
76. private static System.Action GetTaskAction<T1, T2, T3>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3)
77. {
78.     return () => Task.current.Complete(((System.Func<T1, T2, T3, bool>)(System.Func<T1, T2, T3, bool>)System.Delegate.CreateDelegate(typeof(System.Func<T1, T2, T3, bool>), taskImplementer, method))(Param1, Param2, Param3));
79. }
80.  
81. private static System.Action GetTaskAction<T1, T2, T3, T4>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3, T4 Param4)
82. {
83.     return () => Task.current.Complete(((System.Func<T1, T2, T3, T4, bool>)(System.Func<T1, T2, T3, T4, bool>)System.Delegate.CreateDelegate(typeof(System.Func<T1, T2, T3, T4, bool>), taskImplementer, method))(Param1, Param2, Param3, Param4));
84. }
85.  
86. private static System.Action GetTaskAction<T1, T2, T3, T4, T5>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3, T4 Param4, T5 Param5)
87. {
88.     return () => Task.current.Complete(((Func<T1, T2, T3, T4, T5, bool>)(Func<T1, T2, T3, T4, T5, bool>)System.Delegate.CreateDelegate(typeof(Func<T1, T2, T3, T4, T5, bool>), taskImplementer, method))(Param1, Param2, Param3, Param4, Param5));
89. }
90.  
91. private static System.Action GetTaskAction<T1, T2, T3, T4, T5, T6>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3, T4 Param4, T5 Param5, T6 Param6)
92. {
93.     return () => Task.current.Complete(((Func<T1, T2, T3, T4, T5, T6, bool>)(Func<T1, T2, T3, T4, T5, T6, bool>)System.Delegate.CreateDelegate(typeof(Func<T1, T2, T3, T4, T5, T6, bool>), taskImplementer, method))(Param1, Param2, Param3, Param4, Param5, Param6));
94. }
95.  
96. private static System.Action GetTaskAction<T1, T2, T3, T4, T5, T6, T7>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3, T4 Param4, T5 Param5, T6 Param6, T7 Param7)
97. {
98.     return () => Task.current.Complete(((Func<T1, T2, T3, T4, T5, T6, T7, bool>)(Func<T1, T2, T3, T4, T5, T6, T7, bool>)System.Delegate.CreateDelegate(typeof(Func<T1, T2, T3, T4, T5, T6, T7, bool>), taskImplementer, method))(Param1, Param2, Param3, Param4, Param5, Param6, Param7));
99. }
100.  
101. private static System.Action GetTaskAction<T1, T2, T3, T4, T5, T6, T7, T8>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3, T4 Param4, T5 Param5, T6 Param6, T7 Param7, T8 Param8)
102. {
103.     return () => Task.current.Complete(((Func<T1, T2, T3, T4, T5, T6, T7, T8, bool>)(Func<T1, T2, T3, T4, T5, T6, T7, T8, bool>)System.Delegate.CreateDelegate(typeof(Func<T1, T2, T3, T4, T5, T6, T7, T8, bool>), taskImplementer, method))(Param1, Param2, Param3, Param4, Param5, Param6, Param7, Param8));
104. }
105.  
106. private static System.Action GetTaskAction<T1, T2, T3, T4, T5, T6, T7, T8, T9>(object taskImplementer, MethodInfo method, T1 Param1, T2 Param2, T3 Param3, T4 Param4, T5 Param5, T6 Param6, T7 Param7, T8 Param8, T9 Param9)
107. {
108.     return () => Task.current.Complete(((Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, bool>)(Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, bool>)System.Delegate.CreateDelegate(typeof(Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, bool>), taskImplementer, method))(Param1, Param2, Param3, Param4, Param5, Param6, Param7, Param8, Param9));
109. }

Note that this is only garbage-free for 0 to 9 parameters (included).
Over that it reverts to your code, which means that it will work in all cases (which is the most important thing after all).

Also, as I have just tried Panda for half a day, I just tried your examples. They seems to work fine (except the shooter which has some trouble with bullets collisions, but I think it's unrelated to BT).
So, it would be a good idea to try my modification a bit more seriously, even if I'm confident they should work fine.


On a general note, using the type 'object' often leads to garbage collection because of boxing/unboxing.
That's why it's usually better to use generics.
Unfortunately, it's sometimes not very easy, and sometimes it is needed to have one generic method for each number of parameters you need (as in this case).
This problem fades away because it is possible (and advised) to create a small program that generates the generic methods automatically, it's just a matter of generating 50 methods, for 50 parameters.
And if someone, some day, uses more than that, then it will cost him a little garbage, but if he's using more than 50 parameters for one method I doubt that he even knows what garbage is

 

Hi @Gladyon

The GC allocation due to string.Format happens only when the Inspector is displaying the running BT script. That's what the "if (Task.isInspected)" line is for. When the inspector is closed, or completly absent (as it is in a build for instance), there are no GC allocations after the BT script initialization.

I am curious though, how do you avoid GC alloc with StringBuilder and string concatenations. Is there a way to allocate a fixed length string once, then reuse for doing formatting?

There are of course GC allocation when the scripts are compiled and build. A lot of stuff is going there. Optimizations are welcome here, but they have to be significant; I always try to balance optimization with code readability. How much memory is saved with your optimization?

Unity is not thread safe. What would be the use cases for having multi-threaded behaviour trees running concurrently?

The running overhead should be insignificant. Most of the heavy lifting work are done by the tasks, not by the framework. But those are really good questions. Maybe I should create some stress test examples, so we can have some numbers.

 

I have found some garbage generated after the initialization (seen in your shooter example, and I'm not speaking about the garbage generated by the task, but by Panda core), as stated in my first post:
- executing a task with a parameter and a return value
- executing a task that is a property
- executing a task that is a field
These 3 cases generates 17 bytes of GC each (using Unity 2017-1 on a 64 bits Windows 7).
I have provided a fix for the first 2, and the third one isn't fixable on mobile, only on PC, but anybody can use properties instead, so it's not a problem.

In short, StringBuilder have 2 problems, they generate garbage in two places:
- when transforming an integer into a string (by concatenation or formatting)
- when the 'ToString()' method is called

For the first problem, it's just a matter of transforming the integer, float, date, etc. manually. Of course, I say 'just', but it's a lot of code, and a lot of bugs before it works well... especially the date...

The second problem is trickier, you need to access the underlying code of StringBuilder.cs, in order to get the string used internally, and return it.
But this string will not have the correct length because StringBuilder uses a larger than necessary string internally in order to avoid allocating too often, so you need to place a '\0' at the correct position.
And even with that, sometimes it doens't work well, so you also need to access the inner String.cs structure in order to 'cheat' and make it believe it is actually shorter than it really is.

All in all, when you've done that, you have string concatenation and float/int/date to string formatting totally garbage-free.
But in your case, as you have fixed-size displays for the time, it's much easier, you can use a small part of all the things I described.


And as you said, it is for debug only, so the optimization isn't crucial there, it's just that I've spent a lot of time fighting garbage, and it's now a spinal reflex, when I see garbage I eliminate it.

It's the 17 bytes of garbage generated when calling some tasks that are bothering me.
It can grow up fast, and it's additive, which means that the GC will be called more often.
The garbage generated by the debugging display isn't a problem as it won't be in the releases.

But C# is thread-safe, if the data and tasks used aren't using anything from Unity, then it would be possible to run several BT simultaneously provided they do not use shared data.
Of course it would be a little tricky, but to compute the behaviour of a horde of enemies it could be useful.
Each enemy could use the shared data of the world, but in a read-only way, so no multi-threading problem, and their BT would change their internal states.
After a few hundred enemies have been processed, all the internal states can be put back into Unity in the main thread.

That's also a good way of decoupling the game from Unity:
Each frame:
- the relevant data is taken from Unity using the main thread, and put into pure C# objects
- the pure C# objects are processed in parallel if possible
- the modified and relevant data are put back in Unity (positions, rotations, destructions, creations, etc.) using the main thread

I read somewhere that PandaBT could be decoupled from Unity, so that means you've restricted the accesses to Unity in a few classes.
That means it could be possible to do some multithreading, except for the 'Task.Current', I just saw that and it bother me a little.
I understand how useful it is, and how it allows tasks to be even more simple. In order to avoid it I presume tasks would have to have a parameter dedicated to receive the current task, which wouldn't be very readable, and would add a lot of code mostly unused.
I'll think about it to see if I can come up with something.

I'm very interested in stress tests.
In fact, it's one of the first thing I wanted to do after having written a few BT to familiarize myself with it.
Behavior Designer indicates they can run 4000 BT in about 1.4ms, that gives you a reference.

The thing is, I'm pretty sure that the gameObjects will be the limiting factor.
In order to check BT performances properly, it should be applied on non-gameObject, but on standard C# objects, with minimal overhead.

Anyway, I know the performances cannot be miraculous, as the tasks are using their own data, which means the cache misses will be numerous as soon as we're out of the reach of Panda and in game code.
But from what I saw of PandaBT code, I think it should be quite good, I hope you can beat Behavior Designer (I presume they used empty tasks), that would give you an edge to add on the AssetStore presentation page.

 

I'm getting a puzzling error in edit mode (although it does not prevent me from playing the simulation, nor does it cause the simulation to pause when running). The error text reads: "NullReferenceException: Object reference not set to an instance of an object UniversalCommands.get_IsAlive () (at Assets/PBTest/UniversalCommands.cs:726)" Before I continue I should probably explain how "characters" ares set up in my project: The is the abstract class AbstractBase,which contains information like movement speed, max health, is the entity alive, jump height, what kind of shot to fire, etc. All the different class for the player, enemy grunts, and bosses inherit from this class. Then there's the UniversalCommands class, and its child, the BossCommands subclass, which handles the actual "thinking" as well as defining the methods that the BT script will use. Here's the code in question:

Code (CSharp):

1. //this is what I have in UniversalCommands
2.     protected AbstractBase baseEntity;
3.     void Start () {
4.         baseEntity = GetComponent<AbstractBase> ();
5.     }
6. //...
7.     [Task]
8.     public bool IsAlive {
9.         get {
10.             return baseEntity.Alive;//this is line 726
11.         }
12.     }
13. //then in the class BossCommands I have this excerpt:
14.     AbstractBoss boss;
15.      void Start () {
16.         boss = GetComponent<AbstractBoss> ();
17.         baseEntity = GetComponent<AbstractBase> ();
18.     }
19.  

After determining the offending game object by a process of elimination, I have made several observations:
It has a ComplexBoss (the inheritance tree for that class got like this: AbstractBase -> AbstractBoss -> ComplexBoss) script component and a BossCommands component.
Another gameobject in a different scene also has the same script classes attached to them, but does not cause any problems.
Changing any field in the inspector will cause another instance of the error to pop up in the console. Selecting something the the same scene and moving it around can fill the console with dozens of instances the error.

The full text of the error is as follows:

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. UniversalCommands.get_IsAlive () (at Assets/PBTest/UniversalCommands.cs:726)
3. System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
4. Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
5. System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
6. System.Reflection.MonoProperty.GetValue (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] index, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoProperty.cs:297)
7. System.Reflection.MonoProperty.GetValue (System.Object obj, System.Object[] index) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoProperty.cs:283)
8. Panda.BTRuntimeBuilder+<Bind>c__AnonStorey0.<>m__6 ()
9. Panda.BTTask.DoTick ()
10. Panda.BTNode.Tick ()
11. Panda.BTWhile.DoTick ()
12. Panda.BTNode.Tick ()
13. Panda.BTFallback.DoTick ()
14. Panda.BTNode.Tick ()
15. Panda.BTTree.DoTick ()
16. Panda.BTNode.Tick ()
17. Panda.BTProgram.Tick ()
18. Panda.BehaviourTree.Tick ()
19. Panda.BehaviourTree.LateUpdate ()

It's not a critical error, but I fear that it'll cause problems later on.

 

I'd say that's because 'Start()' isn't called in the editor (monobehaviour are usually inactive in the editor), but the BT is probably executed, at least in part, in the editor.
I haven't tried it, but adding 'ExecuteInEditMode' may help:
https://docs.unity3d.com/ScriptReference/ExecuteInEditMode.html

There's a way to be sure, add a log at the start of the 'Start()' and 'IsAlive()' methods.

 

Hi I am thinking of buying the pro version but I have a question for you. Would I be able to use this for a turn based game? Thank you

 

@Gladyon
Thank you for reporting this. I have not spoted this before, I guess it's because I've run my benchmark only with [task] methods and not with fields nor properties. Good catch!

It's annoying that there's no way to get the value of an object without unboxing it first. So it seems the solution is to generate all method signatures with all combinations of types and number of parameters... that's seems to be a bit brutal. I'm not sure if that's the best solution yet I don't know any better. I will research on this problem with the hope that there is a better alternative. You seems to be well experienced about optimizing for GC alloc, let me know if you found something on your side or if you've already been down that path.

 

I have implemented the fixes I've posted, it's true that having 10 different methods in order to match the number of parameters isn't very pretty, but as I generate that code I don't really care.
But it's true that on mobile it may take some memory, but honestly, we're speaking about a few methods probably less than 100, and most surely less than 1000. So, even if each method 100 octets (which I doubt as they are very small), that's only 100Ko of memory, which shouldn't be a problem even on mobiles.

About the fields, I have implemented something to remove the garbage, but it involves creating a DynamicMethod at runtime in order to create the corresponding property.
Unfortunately generating IL code isn't uspported on mobiles, so it wouldn't be a good idea to put that in an asset.
I don't think there's another way, except of course generating C# code in the pre-build, and telling Panda to use the properties generated in pre-build.
That adds a step in the build process, but it should be possible to automate it.
That way, Panda would never use a field, but only methods and properties, which can both be made garbage-less.

 

Hi @lordhamburger
By default the BT Scripts are ticked on Update. But you can tick the script whenever you want. So, you can implement logics that span over several turns. For instance, you can easily implement a unit that uses a hit and run tactic.

 

It tried it, it gets rid of the error, but the AI scripts executes when ever I change a game object's value, such as its position or a public script value in the inspector. This means that every time I try to move or rotate something, the objects with the ComplexBoss script attached will move a bit towards the player (because that's what the bt behavior is set to do).

 

Yes, that's a problem.
That means that in your case you explicitely do not want to execute the BT in the editor.

Panda seems to be designed to be executed in edit mode (there's the 'ExecuteInEditMode' attribute in the 'BehaviourTree' class).


What you can do, is to add a test in your Tasks (or at least some of them) to check if you're in edit mode, and to do nothing if your are.
So, you should remove the 'ExecuteInEditMode' attribute in your own code, and add that code to the tasks that need it:

Code (CSharp):

1. if (Application.isEditor)
2. {
3.     return;     // Or 'return false;' or anything else you need to do in your specific case
4. }
5.  

That way, your boss shouldn't move. in the editor, unless you move it yourself of course.

 

I tried that, but due to the way my code is set up, whenever I hit play all characters that inherited from AbstractBase would end dieing immediately. However I used a slight modified version of your code to fix the problem, so thank you.

Code (CSharp):

1. return baseEntity == null ? false : baseEntity.Alive;

 

@BTCallahan and @Gladyon
The BT scripts are not supposed to be ticked in the editor while not in play mode. That's a bug. It will be fixed in the next release. If you don't want to wait until it is published on the Asset Store, pm me and I will send you a patched version of the package with the fix.

 

Hi Eric, I think I've tried every single BT package that was free in the Asset Store and your's is by far the best and easiest to implement. I'm an educator and like providing plenty of demos and workshops for students with free assets to get them started. You can find my stuff at holistic3d.com/udemy and youtube.com/c/holistic3d. I'm currently working on an AI course for Udemy to come out next week and I was hoping to get your permission to include the free version of Panda BT with the project files I give out.

 

@penny_debyl

Thank you for your interest in Panda BT!

I would like to give you the permission to do so, but I think distributing the asset via any channel other than the Asset Store goes against the Unity's EULA. It would be safer not to include the package with your project files. But I will send a request to Unity to clarify whether this is possible or not.

 

Hi ericbegue, Thank you for creating Panda BT. It's great; I understand the waterfall nature of the scripting language better than node based solutions. I have two things I want to clarify before I leave a review. 1st is the inclusion of Enum types in the latest release. There is no documentation on how these work for free version folks, nor did I see much in this forum. I'm hoping for cleaner state 'while' checks than bools. The 2nd is the ability to access variables to use for my method calls. For example I have several SetGameObject_Active methods for a Sequence that toggles things around, or several waitForDynamicVar methods. I feel like I have to make method variants regularly. Would a [Variable] tag be something that can be implemented? (with bool types fulfilling both [task] as well) I don't care for blackboards as a separate variable pool but I feel like I'm missing something? Either way I am still enjoying Panda; thank you in advance for your response!

 

@OnyDeus
To use enums from BT scripts, just pass the enum value prefixed with the enum type name. For instance, if you have the following enum:

Code (CSharp):

1. enum Stamina{
2.     Low,
3.     Medium
4.     High
5. }

and a [Task] method to set the stamina:

Code (CSharp):

1. [Task]
2. void SetStamina(Stamina value){
3.     this.stamina = value;
4.     Task.current.Succeed();
5. }

Then you use the enum value in a BT script, like this:

Code (CSharp):

1. tree "Rest"
2.     sequence
3.         Wait(15.0)
4.         setStamina( Stamina.High )
5.        

If the enum is within a namespace, prefix the value with the namespace name as well. Panda needs to know the complete name in order to locate the enum value.


Adding support for variables in the BT language would complexify the system a lot. The goal of Panda BT is not to be a full fledged programming language, though I would love to see this happen, I currently don't have time and resources to realize that. But don't forget that you can still do a lot with C#. If you want to have a way to create and use dynamic variables from BT script, you could do something like this:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. using Panda;
6. public class BTVars : MonoBehaviour {
7.  
8.     Dictionary<string, float> vars = new Dictionary<string, float>();
9.  
10.     [Task]
11.     void SetVar(string name, float value)
12.     {
13.         vars[name] = value;
14.         Task.current.Succeed();
15.     }
16.  
17.     [Task]
18.     void IncreaseVar(string name, float step)
19.     {
20.         vars[name] += step;
21.         Task.current.Succeed();
22.     }
23.  
24.     [Task]
25.     void DecreaseVar(string name, float step)
26.     {
27.         vars[name] -= step;
28.         Task.current.Succeed();
29.     }
30.  
31.     [Task]
32.     void isVarGreaterThan(string name, float value)
33.     {
34.         Task.current.Complete( vars[name] > value );
35.     }
36.  
37.     [Task]
38.     void isVarLessThan(string name, float value)
39.     {
40.         Task.current.Complete(vars[name] < value);
41.     }
42.  
43.     [Task]
44.     void isVarBetween(string name, float min, float max)
45.     {
46.         var v = vars[name];
47.         Task.current.Complete( min < v && v < max);
48.     }
49.  
50. }
51.  

You can adapt script to implement a blackboard system by declaring the "vars" static, so that it can be shared over different BT agents.

Hope that helps.

 

Hi

Can you advise on setting the BT script(s) on a behaviour component at runtime? Just once during my init code; not intending to change it after that.

Compile is functionally fine (as below), but in an ideal world I would like to pass it a reference to a BT script (text asset) and see that in the editor window as normal while in play mode. When compiling from the raw text, it obviously just shows something like "(compiled)" in the editor window during play mode.

Code (CSharp):

1. behaviour.Compile(myTextAsset.text);

 

Hi @tylercrammond,

If you want to link the textAssets at run time, you need to assign them to the "scripts" property (it's a array of TextAssets) of the PandaBehaviour component, then call the Apply() method to apply the changes, as follow:

Code (CSharp):

1. var pandaBehaviour = this.gameObject.AddComponent<PandaBehaviour>(); // or GetComponent
2. pandaBehaviour.scripts = textAssets;
3. pandaBehaviour.Apply();

You should see the textAssets on the PandaBehaviour component in the Inspector exactly as you would have done it manually.

 

@ericbegue what do you think of this?

 

@laurentlavigne
Thanks for the video. It's a nice intro to AI planning. I was really curious about the language they created to define the actions, but this part was not shown here.
I'm getting more interested in GOAP, and wondering whether it could be a layer on top of BT or has to be a complete distinct system.

 

Woohoo Eric is considering a GOAP layer, it must Christmas
You can extend the BT language to include goals and preconditions, results and actions, what's inside is the same old panda goodness.
A GOAPBT script could look like this:

Code (CSharp):

1. tree("Root")
2.     //Root behaviour for all unit: Be alive or die.
3.     GOAP
4.         goals
5.             IsAlive (true)
6.             InventoryFull (ITEM.WOODMILL)
7.         actions
8.             // survival
9.             GOAPtree ("flee")
10.             GOAPtree ("defend self")
11.             GOAPtree ("get weapon")
12.             GOAPtree ("walk to weapon")
13.             // gathering
14.             GOAPtree ("gather wood")
15.             GOAPtree ("get axe")
16.             GOAPtree ("add wood to wood mill")
17.             GOAPtree ("walk to tree")
18.             GOAPtree ("drive to tree")
19.             GOAPtree ("walk to fuel")
20.             GOAPtree ("gather fuel")
21.             GOAPtree ("walk to car")
22.  
23. GOAPtree ("walk to tree")
24.     cost
25.         20 * DistanceTo(ITEM.TREE) + InventoryWeight * 0.2
26.     precondition
27.         IsWearing (ITEM.SHOES)
28.     result
29.         IsAt(ITEM.TREE)
30.     action
31.         sequence
32.             SetDestinationToNearby (ITEM.TREE)
33.             GotoDestination
34.  
35. GOAPtree ("drive to tree")
36.     cost
37.         20 * DistanceTo(ITEM.TREE) + InventoryWeight * 0.2
38.     precondition
39.         sequence
40.             VehicleNearby (VEHICLE.CAR)
41.             NearbyVehicleHasFuel
42.     result
43.         IsAt(ITEM.TREE) true
44.     action
45.         sequence
46.             BoardNearby (VEHICLE.CAR)
47.             SetDestinationToNearby (ITEM.TREE)
48.             GotoDestination
49.  
50. GOAPtree ("walk to car")
51.     cost
52.         20 * DistanceToClosest (VEHICLE.CAR) + InventoryWeight * 0.2
53.     precondition
54.         IsWearing (ITEM.SHOES)
55.     result
56.         Has(VEHICLE.CAR) true
57.     action
58.         sequence
59.             SetDestinationToNearby (VEHICLE.CAR)
60.             GotoDestination
61.             Get (VEHICLE.CAR)
62.  
63. GOAPtree ("refuel")
64.     cost
65.         0.1
66.     precondition
67.         Has(VEHICLE.CAR)
68.         InventoryContains(RESOURCE.FUEL)
69.     result
70.         VehicleHasFuel true
71.     action
72.         FuelUpNearbyVehicle
73.  
74. GOAPtree ("walk to fuel")
75.     cost
76.         20 * DistanceTo(RESOURCE.FUEL) + InventoryWeight * 0.2
77.     precondition
78.         IsWearing (ITEM.SHOES)
79.     result
80.         IsAt(RESOURCE.FUEL) true
81.     action
82.         sequence
83.             SetDestinationToNearby (RESOURCE.FUEL)
84.             GotoDestination
85.  
86. GOAPtree ("gather fuel")
87.     cost
88.         0.2
89.     precondition
90.         sequence
91.             IsAt (RESOURCE.FUEL)
92.             HasSpaceInInventory
93.     result
94.         InventoryContains(RESOURCE.FUEL) true
95.     action
96.         Grab(RESOURCE.FUEL)
97.      
98.  
99. GOAPtree ("gather wood")
100.     cost
101.         1.5
102.     precondition
103.         sequence
104.             HasToolInHand
105.             IsWearingProperAttire
106.             IsAt(ITEM.TREE)
107.             HasSpaceInInventory
108.     result
109.         InventoryContains(RESOURCE.WOOD) true
110.     action
111.         sequence
112.             Attack (ITEM.TREE)
113.             Grab(RESOURCE.LOG)
114. etc...
115.  

this bit

Code (CSharp):

1.     result
2.         InventoryContains(RESOURCE.WOOD) true

Is not very Panda, the idea is that conditions turn true or false as a result for the planer to build a graph

 

Hi @laurentlavigne,

I think it would be best to have the GOAP layer separated from the BT layer. What I am thinking of, is to have the GOAP action definitions also in simple text files, but not in BT scripts. Yet the action would be implemented as BT tree. That is the GOAP layer would plan the actions given the actions definition and the current state of the world, then the actual actions will be executed with BT trees.

The definition of the actions should consist of the following part.
* prerequisites: the conditions required to execute the actions, expressed as a logical expression
* cost: a value, or an expression computing the cost of the action
* action: the action itself, which tree should be run for performing the action
* outcome: the state of the world after the actions has been executed, with could be expressed as several assignment expressions.

Since the prerequisite, cost and outcome can be complex expressions, I am considering to delegate this part to a 3rd party scripting language, maybe lua.

Also, I need to figure out how tho handle the variables describing the world state. These variables have to match the game state when initiating the planning, then they would get updated during the planning, as a small simulation to compute the best action sequence to realize the goal.

 

Give me a example.

 

Hi @ericbegue ,

I'm testing the PandaBT free, and I have some questions:

tree("AvoidPlayer")
while not IsIt
sequence
IsPlayerNear [return void, but use Task.current.Complete]
SetDestination_Random [return bool]
IsDirectionSafe [return bool]
MoveToDestination [return void, Task.current.Complete]

I understand that the sequence goes from first to last child, and by the moment any child fails the sequence will be interrupted. but why some tasks return a bool, while others use Task.Complete?

Thanks!

 

Hi @EvandroLins,

In a MonoBehaviour, a task implementation can be one of the following symbols tagged with the [Task] attribute:
- void method
- bool method
- bool property
- bool variable

When implementing a task with a void method, to complete the task, it is required to call either:
- Task.current.Succeed()
- Task.current.Fail()
- Task.current.Complete( someBoolean )
(The task is kept running until one of the above is called).

Whereas with a boolean (method, variable or property), the task completes immediately. That is, it completes the first time it has been ticked; it is never running.

Boolean tasks are a short way to write tasks that are not required to run over several frames. You could also, write these type of tasks using void method and calling Task.current.*, the BT script would work the same. It just a way to avoid too much typing.
For instance:

Code (CSharp):

1. [Task]
2. void IsEnemyVisible()
3. {
4.     if( someCondition )
5.         Task.current.Succeed();
6.     else
7.         Task.current.Fail();
8. }

Is the same as:

Code (CSharp):

1. [Task]
2. bool IsEnemyVisible;

 

Hi, I downloaded Panda BT tonight and read through the docs. I could not find a Youtube video on starting a project from scratch and implementing Panda, but there was a Woodcutter which explained enough.

I am stuck on something probably simple. The Component Panda Behavior script is not seeing my AI script?
1. I created a empty GameObject in the hierarchy.
2. I added the component Panda Behavior (script)
3. Im my project folder I created ThePanda BT script and called it 'AI.BT'
4. I created a C# script and added it to the same GameObject as the Panda Behavior is on with this code.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using Panda;
5.  
6. public class AI_Script : MonoBehaviour {
7.  
8.     // Use this for initialization
9.     void Start () {
10.        
11.     }
12.  
13.     [Task]
14.     public void helloWorld()
15.     {
16.         print("I am Alive!");
17.         Task.current.Succeed();
18.     }
19. }

But now in the Inspector, how do I add the helloWorld() method to the Panda Behavior script?

Thanks!

 

I think I figured it out. I need to manually enter the stuff into the BT.txt file. It showed up and worked.

 

Hi @larswik,

Yes, that's how the task is supposed to be used from the BT script: just type the task name (and the parameters when applicable). The system will then search for the task implementation on any MonoBehaviours attached on the game object, looking for the [Task] attribute.

For information, the pro edition comes with an in-Inspector drag&drop style Editor, where the available tasks are listed in a menu or a combo-box when inserting new nodes into the tree. It allows to edit and tweak the BT directly from the Inspector.

 

Implemented PandaBT and love it. However, I have hit a snag and have a question. I have multiple NPCs that could have different jobs. So my thought was to implement a tree like so:

Code (CSharp):

1. ...
2. tree("employed")
3.     while not isUnEmployed
4.         while not isWorking
5.             fallback
6.                 tree("work")
7.  
8. tree("work")
9.     sequence
10.         GoToWork
11.         ArriveAtDestination
12.         GetTask
13.         GoToTask
14.         ArriveAtDestination
15.         DoWork
16. ...

And then have different scripts for different jobs (lumberjack, miner, etc.). Those scripts each have a task defined for
GoToWork
ArriveAtDestination
GetTask
GoToTask
ArriveAtDestination
DoWork
The problem is that Panda complains that the Tasks are defined in multiple scripts. I tried removing the script component and swapping it out for the job script that fits the NPC's task, however, that fails as well (null reference exception).

What is the "Panda way" to achieve this?

Thank you

 

@mtdev01

Do you mean the same agent can change its job at runtime, and each job type has its own implementation of tasks in different MonoBehaviours?

The problem is the PandaBehaviour check the components attached to the gameObject for tasks when they are added or removed. So if there are tasks missing or duplicated, it will raise an exception.

The safest way to swap MonoBehaviours at runtime, would be to unlink the BT scripts from the PandaBehaviour component and then swap the MonoBehaviours implementing the job tasks, before recompiling the scripts:

Code (CSharp):

1. var scripts = pandaBehaviour.scripts;
2. // Unlink the BT scripts by compiling a dummy tree
3. pandaBehaviour.scripts = null
4. pandaBehaviour.Compile("tree(\"root\")\n\tSucceed\n");
5.  
6. // Remove the MonoBehaviours implementing the old job
7. // Add the MonoBehaviours implementing the new  job
8.  
9. // Reattach the BT scripts
10. pandaBehaviour.scripts = scripts;
11. pandaBehaviour.Apply();

 

That is what I meant and this is probably just what I was looking for. Thank you!

 

@mtdev01

By the way.

Code (CSharp):

1. tree("employed")
2.     while not isUnEmployed
3.         while not isWorking
4.             fallback
5.                 tree("work")
6.                

That can also be written with only one while node:

Code (CSharp):

1. while
2.     sequence
3.         not isUnEmployed
4.         not isWorking
5.     tree("work")
6.                

The sequence acts like a logical AND. If later on, you'd need a logical OR use a fallback node.

 

@laurentlavigne

Code (CSharp):

1. GetAxe
2.     condition: hasAxe = false
3.     result: hasAxe = true
4.     cost: 2.0
5.  
6. CollectBranches
7.     condition: hasFireWood = false
8.     result: hasFireWood = true
9.     cost: 9.0
10.  
11. CutWood
12.     condition: hasAxe = true
13.     result: hasFireWood = true
14.     cost: 1.0
15.  
16. MoveToShop
17.     condition: knowsShopLocation = true
18.     result: atShopLocation = true
19.     cost: distanceToShopLocation/speed
20.  
21. BuyAxe
22.     condition: atShopLocation && hasAxe = false && gold >= 50
23.     result: hasAxe = true; gold = gold - 50;
24.     cost: 1.0
25.  
26. MakeFire
27.     condition: hasFire = false && hasFireWood
28.     result: hasFire = true; hasFireWood = false;
29.     cost: 2.0
30.  

 

This is Very clean.
So this is the txt file in this planning language and GetAxe is also present as a tree ("GetAxe") in the panda txt?

 

That's exactly the idea.

 

I love it.

 

Hey Eric, I love your behavior tree. It's exactly what I was looking for. There is one issue though; the Random structural node only statically assigns the weights (for example random(1,2,3)). I want it to be able to dynamically assign weights at runtime. For example, depending on the state of the code, the weights for the Random node would be random(var1,var2,var3). Any thoughts on this?

 

@ericbegue

Goap could be written in a Class instead of text file ? Would it be better ?

Code (CSharp):

1.  
2.  
3.  
4. Class BuyAxe{
5.  
6. float cost = 1;
7.  
8. bool condition(){
9.  return ( atShopLocation && hasAxe == false && gold >= 50);
10. }
11.  
12. void result(){
13.  hasAxe = true; gold = gold - 50;
14. }
15.  
16. }

 

He usually answers in a day so he might be busy.
Panda doesn't have a blackboard so if you need to store variable you create a variable inside your c# code and have a task to set it.
For example

Code (CSharp):

1. float weight;
2. [Task]
3. void SetRandomWeight(float w)
4. {
5.    weight = w;
6. }
7.  
8. [Task]
9. void ConsumeRandomWeight()
10. {
11.     // do something with 'weight'
12. }

 

Hello,

I love your asset. I've been playing around with it and I love its simplicity.
There was one thing I couldn't figure out on my own how to do and the documentation and examples don't seem to have this type of thing and I'm guessing it's not possible to do.

Is it possible to have variables as parameters in the tree so I can control the parameter from the inspector ?

for example :

Code (CSharp):

1. [Task]
2. public float Cooldown = 0;
3.  
4. ----------------------------------------------------
5.  
6. tree("Root")
7.     while IsAlive
8.         sequence
9.             EnemyInRange
10.             AttackEnemy
11.             Wait Cooldown

I want to upgrade this character and modify its attack speed ( reduce waiting time ).

Thank you ^-^

 

You can do something like

Code (CSharp):

1. [Task]
2. public float cooldown = 1;
3. [Task]
4. public bool WaitForCooldown()
5. {
6.             var task = Task.current;
7.             var info = task.item != null? (WaitFloatInfo)task.item: (WaitFloatInfo)(task.item = new WaitFloatInfo());
8.  
9.             if (task.isStarting)
10.             {
11.                 info.elapsedTime = -Time.deltaTime;
12.             }
13.  
14.             info.elapsedTime += Time.deltaTime;
15.            
16.             if (Task.isInspected)
17.             {
18.                 float tta = Mathf.Clamp(cooldown - info.elapsedTime, 0.0f, float.PositiveInfinity);
19.                 task.debugInfo = string.Format("t-{0:0.000}", tta);
20.             }
21.  
22.             if (info.elapsedTime >= cooldown)
23.             {
24.                 task.debugInfo = "t-0.000";
25.                 task.Succeed();
26.             }
27. }

 

bug: when panda can't bind to a component because that component class name != file name, panda doesn't show the panda script at all

 

How can I invoke a tree using a variable? I wish to avoid a sequence of trees with each tree having "while someFlag" at the top. This doesn't work, but conveys the general idea:

MonoBehaviour:

Code (CSharp):

1. public class Entity : MonoBehaviour
2. {
3.     string _job;
4.  
5.     [Task]
6.     public string Job
7.     {
8.         get { return _job;  }
9.     }
10.  
11.     [Task]
12.     void Console(string txt)
13.     {
14.         Debug.Log(txt);
15.     }
16. }

BT text:

Code (CSharp):

1. tree("Root")
2.     parallel
3.         repeat mute tree(Job)
4.  
5. tree("job1")
6.     Console("doing job1")
7.  
8. tree("job2")
9.     Console("doing job2")
10.  
11. tree("job3")
12.     Console("doing job3")

 

Is there documentation or examples of how PandaBehaviour.snapshot is supposed to work? I keep getting this error:

Code (CSharp):

1.  
2. NullReferenceException: Object reference not set to an instance of an object
3. Panda.BTProgram.set_snapshot (Panda.BTSnapshot value) (at Assets/PandaBehaviour/Core/Panda/BT/BTProgram.cs:305)
4. Panda.BehaviourTree.set_snapshot (Panda.BTSnapshot value) (at Assets/PandaBehaviour/Core/PandaUnity/BehaviourTree.cs:418)
5. Test2.FixedUpdate () (at Assets/Test2/scripts/Test2.cs:59)
6.