WEBVTT 00:06.820 --> 00:08.140 Welcome back. 00:08.470 --> 00:13.450 So we have our custom service and so far it doesn't do a whole lot for us. 00:13.450 --> 00:15.220 It just prints a debug message. 00:15.220 --> 00:17.410 Now I'd like to gather information. 00:17.410 --> 00:21.640 I'd like to find the nearest player and then we can set variables. 00:21.640 --> 00:24.310 Now where do we store these variables. 00:24.310 --> 00:26.830 Are they going to be on the service itself? 00:26.830 --> 00:30.190 Well no the service is not where we store variables. 00:30.430 --> 00:32.650 Is it going to be on the behavior tree itself? 00:32.650 --> 00:36.730 Well actually no, the behavior tree doesn't store variables either. 00:36.730 --> 00:43.240 What we do is we designate a specific asset to store the variables that the behavior tree will use, 00:43.240 --> 00:45.640 and that asset is the blackboard. 00:45.640 --> 00:52.270 Let's click on that blackboard tab and we'll see that right here we have all the keys right under the 00:52.270 --> 00:53.920 keys category. 00:53.920 --> 00:56.290 So there's a reason it's called the blackboard. 00:56.290 --> 01:04.750 Blackboard also known as chalkboard is what you would see in a typical old school classroom where the 01:04.750 --> 01:09.700 instructor is putting things on the blackboard with a piece of chalk. 01:09.820 --> 01:16.690 Think of this as a chalkboard used by the behavior tree, where we can put variables and their values, 01:16.690 --> 01:18.670 and we can update those values. 01:18.820 --> 01:23.620 The behavior tree has access to the blackboard that it's associated with. 01:23.620 --> 01:31.330 And here in the behavior tree we can access those values and behave based on what those values are. 01:31.750 --> 01:35.950 By default the blackboard has a self actor. 01:36.070 --> 01:41.740 Self actor is a blackboard key and the key type is object. 01:41.740 --> 01:43.750 But we can change the key type. 01:43.870 --> 01:51.040 If we click the dropdown, we'll see that there are a lot of different types that our keys can be of, 01:51.040 --> 01:57.460 and we can even pass in the values of keys into our nodes on our blackboard. 01:57.460 --> 02:05.500 For example, find nearest player could have a variable of type blackboard key if we wanted to and we 02:05.500 --> 02:06.760 can pass it in here. 02:06.760 --> 02:10.840 We can take one of our blackboard keys and pass it straight in. 02:10.840 --> 02:16.330 The way we would do that is we would go into our service blueprint and add a variable. 02:16.330 --> 02:24.550 And we can call this self actor key and change its type to key. 02:24.550 --> 02:27.970 And the type is actually blackboard key selector. 02:27.970 --> 02:31.180 If we choose blackboard key selector for the type. 02:31.180 --> 02:39.190 And we open the eye icon here and compile, then all of a sudden this self actor key variable, if we 02:39.190 --> 02:46.930 go back to our blackboard, is something that we can set on this particular node that we've attached 02:46.930 --> 02:47.830 to our selector. 02:47.830 --> 02:49.780 Here it is in the details panel. 02:49.780 --> 02:51.610 It's self actor key. 02:51.610 --> 02:56.230 And we can set it to one of our key values in our blackboard. 02:56.230 --> 03:01.360 Now if we expand the dropdown we see that there's only one option that we can set for this. 03:01.360 --> 03:10.000 And it's the self actor that we have now if we have this set then we can use it here in our service. 03:10.000 --> 03:17.770 If I take my self actor key and get it and then drag off of it, we can get the value stored in that 03:17.770 --> 03:19.480 blackboard key selector. 03:19.510 --> 03:25.480 Now we don't know what self actor key is we actually do because we know that we're setting it equal 03:25.480 --> 03:27.790 to self actor which has the object type. 03:27.790 --> 03:31.450 But really this behavior tree service doesn't know that. 03:31.450 --> 03:37.750 But we can drag off of self actor key and type get blackboard value as. 03:37.750 --> 03:43.540 And notice we can get the blackboard value as any of these types that a key can be. 03:43.540 --> 03:50.440 So if we choose object which we know this is the type, then we're accessing the value stored in that 03:50.440 --> 03:50.860 key. 03:50.860 --> 03:58.840 If it's set now because this is an object we can drag off and type get object name, which is a blueprint 03:58.840 --> 04:02.890 function node we can get and we can print this string here. 04:02.890 --> 04:05.290 And why don't we just see what it says. 04:05.290 --> 04:11.590 If we press play then we can see goblin spear and goblin slingshot printed to the screen. 04:11.590 --> 04:13.510 Now what does this tell us? 04:13.510 --> 04:20.410 This tells us that we automatically have a key in our blackboard called Self Actor. 04:20.410 --> 04:22.240 And what is it set to? 04:22.240 --> 04:28.330 Well, it's set to the character, the character associated with this behavior tree. 04:28.630 --> 04:31.990 So at least we already have one blackboard key. 04:31.990 --> 04:39.250 And we now know that we can add a variable of type blackboard key selector to a behavior tree service 04:39.250 --> 04:43.810 blueprint and expose that to the details panel. 04:43.810 --> 04:49.150 And if we do that then we can set the value based on one of our blackboard keys. 04:49.150 --> 04:50.740 So that's kind of cool. 04:50.740 --> 04:57.310 But because I don't need that right now I'm going to go ahead and just remove all that and remove self 04:57.310 --> 04:59.620 actor key compile and save. 04:59.620 --> 05:03.520 And I'll come back and see that that's no longer in the details panel there. 05:03.790 --> 05:06.070 I really don't need to pass self actor. 05:06.380 --> 05:08.300 And to find nearest player. 05:08.300 --> 05:13.760 What I really want is for find nearest player to do its job. 05:13.760 --> 05:18.200 Find the nearest actual character controlled by a human player. 05:18.200 --> 05:18.800 Right? 05:19.250 --> 05:24.950 And once I find that player, I'd like to set the value of one of my blackboard keys, but not self 05:24.950 --> 05:25.670 actor. 05:25.670 --> 05:32.690 I want a blackboard key for a target for this particular AI character to follow. 05:32.720 --> 05:39.800 I'd like a blackboard key based on object that I can move towards and potentially attack. 05:39.800 --> 05:43.190 So I'm going to add a new key to my blackboard. 05:43.190 --> 05:47.480 And I go back to my blackboard tab to do that and click on New Key. 05:47.480 --> 05:49.280 And I can choose the type for it. 05:49.280 --> 05:50.990 It's going to be object. 05:50.990 --> 05:56.120 And this object I'd like to call target to follow. 05:56.330 --> 05:58.640 And we see that its key type is object. 05:58.640 --> 06:01.100 Now notice key type has a drop down. 06:01.100 --> 06:06.950 And for the base class we can change it from object to really any base class we like. 06:06.950 --> 06:13.310 And that would make this act kind of like a subclass of it'll restrict it to that type or lower in the 06:13.310 --> 06:14.210 hierarchy. 06:14.480 --> 06:16.070 And we can choose actor. 06:16.070 --> 06:21.560 And I'd like to choose actor for target to follow so that we can only follow actors. 06:21.560 --> 06:28.430 And there are certain things in our behavior tree that we can do with actors that we can't do with objects, 06:28.430 --> 06:30.380 and we'll learn about those soon. 06:30.710 --> 06:36.980 Now, if we were to check this one instance synced, then that would mean that this field would be synchronized 06:36.980 --> 06:39.440 across all instances of this blackboard. 06:39.440 --> 06:45.710 Now we have multiple enemies, potentially all using this blackboard and instance synced would make 06:45.710 --> 06:48.380 this variable shared among all of them. 06:48.380 --> 06:52.820 If one of them sets it, then all of them have access to that same variable. 06:52.940 --> 06:58.940 But if it's unchecked, then each instance of the blackboard has its own version of that variable. 06:59.360 --> 07:02.510 So now we have a target to follow blackboard key. 07:02.540 --> 07:07.610 I'd also like another key for the distance to that target. 07:07.610 --> 07:09.860 And that's going to be a float key. 07:09.860 --> 07:17.090 I'm going to call this one distance to target because I'd like to set that as soon as I find the nearest 07:17.090 --> 07:17.780 player. 07:17.780 --> 07:20.330 And then we can act based on distance. 07:20.330 --> 07:26.750 So now that we have these keys, we can flesh out what our behavior tree service does, how it actually 07:26.750 --> 07:28.220 finds the nearest player. 07:28.220 --> 07:35.330 So back here in our behavior tree service, the first step to finding the nearest player is getting 07:35.330 --> 07:36.320 all players. 07:36.320 --> 07:44.630 Now if I'm going to say get all actors of a certain class, maybe it's the character class, for example, 07:44.630 --> 07:50.090 that's going to include all actors of the character class, including all the enemies. 07:50.090 --> 07:55.760 But we want only those characters that are controlled by a human player. 07:56.030 --> 07:58.040 So how do we make that distinction? 07:58.580 --> 08:05.000 Well, one way is through tags, and I'm not talking about gameplay tags like what we've been using, 08:05.000 --> 08:11.240 but there are actor tags that are basically set with f names on actors. 08:11.450 --> 08:18.320 We can identify actors with actor tags pretty easily, and these tags are exposed to the details panel 08:18.320 --> 08:21.830 for all actors, and we can set those tags. 08:21.830 --> 08:30.260 I can go into blueprints into character, and I can open BP enemy base, and in the details panel I 08:30.260 --> 08:32.120 can simply search for tags. 08:32.120 --> 08:38.750 Now here we have under advanced tags, it says an array of tags that can be used for grouping and categorizing. 08:38.990 --> 08:43.400 So these are almost as useful as gameplay tags but they're a little more simple. 08:43.400 --> 08:45.200 They're based on f names. 08:45.200 --> 08:48.230 If we click plus we can add one of these. 08:48.230 --> 08:53.270 For example the base enemy class could just have the tag enemy. 08:53.870 --> 08:56.330 And we can always check an actor for its tags. 08:56.330 --> 08:59.720 We don't have to cast to Ora enemy or anything like that. 08:59.720 --> 09:01.760 We can just check the actor tags. 09:01.760 --> 09:04.340 So this makes it really nice and useful. 09:04.340 --> 09:09.710 And if we want to distinguish between, say, Ora and any of the enemies, the enemies could have the 09:09.710 --> 09:13.910 enemy tag and Ora could have, say, a player tag. 09:13.910 --> 09:21.860 So I can open BP Ora character and search for tags, and I can add a tag for Ora and this can be player. 09:21.860 --> 09:27.500 Then by checking these tags, we always know if we're dealing with an enemy or if we're dealing with 09:27.500 --> 09:28.100 Ora. 09:28.100 --> 09:31.220 So after doing that I'm going to save all. 09:32.450 --> 09:36.650 So here is where we're going to try to find the nearest player. 09:36.770 --> 09:42.440 Before we do, I'm going to add a couple of variables to this behavior tree task. 09:42.440 --> 09:50.690 And the type for these variables is going to be blackboard key selector. 09:50.720 --> 09:55.190 This is a struct for generic blackboard keys. 09:55.190 --> 09:57.320 So we have a blackboard key selector. 09:57.320 --> 10:02.300 The first one is going to be called target to follow. 10:03.850 --> 10:05.710 Underscore selector. 10:05.860 --> 10:09.130 So we have a target to follow blackboard key selector. 10:09.130 --> 10:15.220 We're going to add another one called distance to target selector. 10:15.400 --> 10:21.130 This will allow us to make a link between this service and our blackboard keys. 10:21.130 --> 10:25.900 So we have those for whenever we find the nearest player. 10:25.900 --> 10:33.970 But the player may not be an aura if this behavior tree belongs to a pet that's following aura around, 10:33.970 --> 10:38.410 well, it's nearest player from its perspective may be an enemy. 10:38.410 --> 10:46.690 So now that we have tags on both aura and on enemies that we can use to identify whether they're players 10:46.690 --> 10:53.230 or enemies, we can find all actors with one of the two tags, either player or enemy. 10:53.230 --> 11:01.300 If our controlled pawn is a player as or as pet would have in that hypothetical case, then we'd want 11:01.300 --> 11:03.310 to find all actors with the enemy tag. 11:03.310 --> 11:10.540 But if the controlled pawn has the enemy tag, we'd like to find all actors with the player tag and 11:10.540 --> 11:11.020 so on. 11:11.020 --> 11:18.160 So what we can do is have a tag for the target of this AI controlled pawn. 11:18.160 --> 11:19.840 We can add a new variable. 11:19.840 --> 11:24.760 We can call it target tag, but this can be an F name. 11:24.760 --> 11:31.270 Because these actor tags are implemented as f names, they're simpler than gameplay tags and we can 11:31.270 --> 11:33.970 check our controlled pawn. 11:34.330 --> 11:37.360 We can see if it has a tag we can use. 11:37.360 --> 11:39.970 The function actor has tag. 11:40.740 --> 11:47.880 Now, if the actor has the tag player, then the target tag is going to be enemy. 11:47.880 --> 11:53.280 So let's put a branch here and we'll set target tag to enemy. 11:54.640 --> 12:01.780 Otherwise the actor does not have the player tag, and we'll just assume that it has the enemy tag and 12:01.780 --> 12:08.380 its target tag will be player, which is the case for our goblins, right? 12:08.620 --> 12:14.710 So this could be collapsed to a function and we can call this set target tag. 12:16.210 --> 12:23.260 And the input parameter is going to be what this input is controlled pawn. 12:23.260 --> 12:26.380 So the first thing we do is we set the target tag. 12:26.380 --> 12:32.020 Then all we have to do is find all actors with the tag we can use. 12:32.020 --> 12:35.110 Get all actors with tag. 12:35.660 --> 12:37.370 Passing in the target tag. 12:37.370 --> 12:41.990 And this gives us an array of all the actors that have this tag. 12:42.170 --> 12:46.730 Now, if this eye is an enemy, this will be all the players. 12:46.850 --> 12:50.720 And if this eye is a player, this will be all the enemies. 12:50.990 --> 12:54.770 So we can prove this with a for each loop. 12:54.770 --> 12:57.890 And in the for each loop we'll take the array element. 12:57.890 --> 13:04.850 We'll call get object name, and we'll print that name just to prove that this array contains what we 13:04.850 --> 13:06.350 think it contains. 13:06.380 --> 13:11.900 In the case of a game where there's one aura, we'll see one aura printed to the screen. 13:11.930 --> 13:17.810 Of course we'll see three messages because we have three goblins every 0.5 seconds. 13:17.810 --> 13:18.800 Let's check it out. 13:19.650 --> 13:20.760 There we go. 13:20.760 --> 13:24.090 All of them are finding aura perfect. 13:24.090 --> 13:26.520 So that's as expected. 13:26.520 --> 13:31.050 We now have all actors with the target tag. 13:31.050 --> 13:37.920 The next thing we need to do is find the nearest of these actors, and we'll implement that algorithm 13:37.920 --> 13:38.730 next. 13:39.360 --> 13:40.320 I'll see you soon.