WEBVTT 00:06.870 --> 00:08.340 Welcome back. 00:08.610 --> 00:15.420 So our goal here is to get our enemies moving around and being active and being controlled by AI. 00:15.750 --> 00:19.980 Now we know that there are currently associated with a behavior tree. 00:19.980 --> 00:23.220 If we go to our blueprints folder, go to AI. 00:23.250 --> 00:25.020 We have a behavior tree. 00:25.050 --> 00:28.350 Now the behavior tree has a root node. 00:28.350 --> 00:32.370 And from the root node we can attach something. 00:32.370 --> 00:37.020 We can attach children to nodes in our behavior tree. 00:37.260 --> 00:42.750 Now one of the fundamental nodes that you can have in the behavior tree is the selector node. 00:43.170 --> 00:50.460 A selector node has the very specific quality that it will execute its children from left to right. 00:50.460 --> 00:56.610 And by children I mean I can drag off of the bottom of my selector and put nodes. 00:56.820 --> 00:58.200 We know what tasks do. 00:58.230 --> 01:06.180 We've seen the play animation task node, and there are a number of other built in tasks such as wait 01:06.510 --> 01:10.320 and other things such as move to. 01:10.350 --> 01:14.520 So these are tasks which perform some kind of action. 01:14.520 --> 01:20.850 Now when we have things connected to the bottom of a selector, we say that these nodes are children 01:20.850 --> 01:27.390 of the selector and the selector will execute them left to right, one at a time. 01:27.570 --> 01:32.430 Now it doesn't just do this all at the same time, but one after the other. 01:32.430 --> 01:36.960 In other words, it's going to use this play animation node and it's going to stop. 01:36.960 --> 01:42.720 It'll be held up here until the play animation node finishes, at which point it will then go to the 01:42.720 --> 01:43.860 next node. 01:43.860 --> 01:47.910 And once that node has finished, it will then go to the next node. 01:48.120 --> 01:54.960 Now, nodes in a behavior tree have the concept of success or failure, and whether a node succeeds 01:54.960 --> 01:59.670 or fails depends on the node and how it defines success or failure. 01:59.700 --> 02:07.200 Now, if a node succeeds or fails, it returns that success or failure information back to its parent, 02:07.200 --> 02:11.250 and the parent will then decide what to do with that information. 02:11.460 --> 02:18.630 A selector specifically has the quality that it will execute its children, one after the other, until 02:18.630 --> 02:24.930 one of its children succeeds, at which point it will then return success up to its parent. 02:25.470 --> 02:30.240 Now, once success returns to the root, then the whole tree starts over. 02:30.240 --> 02:36.690 So a selector with three children like this will execute its first child first. 02:36.690 --> 02:40.650 And if that child succeeds, it'll never get to the other children. 02:40.650 --> 02:47.550 And once it returns success to the root and starts over, if it succeeds again, then once again, we 02:47.550 --> 02:50.640 will never try to execute the other two child nodes. 02:50.640 --> 02:55.830 It will only ever keep executing the first node as long as it keeps succeeding. 02:55.860 --> 03:03.030 As soon as it fails though, then the selector will try to execute the next of its child nodes and continue 03:03.030 --> 03:04.170 the process from there. 03:04.170 --> 03:06.720 So that's the behavior of a selector. 03:07.080 --> 03:10.740 Now selectors can have things attached to them. 03:10.740 --> 03:18.720 We call a selector a composite node, and we can attach certain types of nodes to composite nodes and 03:18.720 --> 03:19.440 tasks. 03:19.440 --> 03:25.560 One of these types of nodes that I'd like to attach to my selector is called a service. 03:25.650 --> 03:32.130 Now I can right click on my selector and notice that we can add decorators and services. 03:32.130 --> 03:38.460 Decorators can be attached to nodes, and services can be attached to nodes. 03:38.460 --> 03:42.420 Notice that there are a number of different types of decorators. 03:42.720 --> 03:45.540 And we'll get to decorators in more detail later. 03:45.540 --> 03:53.400 But I'd like to add a service and a service once attached to a node, such as a selector will execute 03:53.400 --> 03:58.800 at its defined frequency as long as the branch is being executed. 03:58.800 --> 04:05.580 Now this selector is considered a branch, and even if it has multiple children connected to it, we 04:05.580 --> 04:09.330 consider the selector and all of its children to be a branch. 04:09.330 --> 04:17.130 If this branch is being executed, then any services attached to it will be executed and services execute 04:17.130 --> 04:19.410 at a frequency that we specify. 04:19.410 --> 04:26.340 They have their own tick functionality, but generally in behavior trees we don't often have things 04:26.340 --> 04:28.470 tick every single frame of the game. 04:28.470 --> 04:30.300 Like your typical tick function. 04:30.300 --> 04:34.680 We tick every so often, every half second, every quarter second. 04:34.680 --> 04:38.880 We specify how often our services can tick. 04:38.880 --> 04:45.630 Now, if I wanted to attach a service on here, I could or I can create my own. 04:45.630 --> 04:52.230 And that's what I'd like to do, is create my own service that will do exactly what I tell it to do 04:52.230 --> 04:53.820 every time it ticks. 04:53.820 --> 04:56.910 And for that, we need a new class. 04:57.510 --> 05:03.870 Hey there, it's Steven from the future here, and I'm coming back to let you know about a mistake that 05:03.870 --> 05:05.490 I made in the course. 05:05.490 --> 05:06.360 And how. 05:06.520 --> 05:08.620 How we're going to rectify it. 05:08.620 --> 05:17.860 You see, in the original version of this video, we created a new class for our behavior tree service, 05:17.860 --> 05:20.140 and we created that class in C plus. 05:20.140 --> 05:20.890 Plus. 05:20.890 --> 05:29.260 The class we created was based on UT Service Blueprint Base, which is designed to be subclassed in 05:29.260 --> 05:30.460 blueprint only. 05:30.460 --> 05:32.170 We can see the comment here. 05:32.170 --> 05:34.960 Base class for blueprint based service nodes. 05:34.960 --> 05:38.290 Do not use it for creating native C plus plus classes. 05:38.290 --> 05:44.440 This is the no no that I actually did in the course, and it's kind of silly. 05:44.440 --> 05:46.450 The class is called Blueprint Base. 05:46.450 --> 05:54.040 I don't know why I didn't snap there, but I created the class in C plus plus and this class is made 05:54.040 --> 05:56.380 to be Subclassed in blueprint. 05:56.380 --> 05:58.990 That's the appropriate way to subclass this class. 05:58.990 --> 06:00.880 That's how we're actually going to do it. 06:00.880 --> 06:04.720 But the original version of the course created it in C plus. 06:04.720 --> 06:10.270 Plus it still worked, but it just wasn't using the class the way it was designed to be used, which 06:10.270 --> 06:15.310 is as a blueprint rather than a native C plus plus class. 06:15.310 --> 06:21.550 So if you go and look at the GitHub commit for this lecture, you're going to see this behavior tree 06:21.550 --> 06:26.890 service C plus plus class based on UT Service Blueprint base. 06:26.890 --> 06:33.520 You can safely ignore that because we're going to be creating it in blueprint as is intended. 06:33.520 --> 06:41.110 So completely ignore the GitHub commit for this lecture as we're not going to create this class in C 06:41.110 --> 06:41.920 plus plus. 06:41.920 --> 06:44.200 Instead we're going to create it in blueprint. 06:44.200 --> 06:52.330 So we can go into our I folder and create our new behavior tree task directly. 06:52.330 --> 06:53.710 Here we can right click. 06:53.710 --> 06:55.960 We can create a new blueprint class. 06:55.960 --> 07:03.640 And we're going to open all classes and search for BT Service Blueprint Base. 07:03.640 --> 07:06.880 This is what we're going to create a blueprint based on. 07:06.880 --> 07:08.500 So let's make this blueprint. 07:08.500 --> 07:13.630 And we're going to prefix its name with Pts for behavior tree service. 07:13.630 --> 07:21.340 And I'd like to call this Find nearest player because I want this service to do just that. 07:21.340 --> 07:25.060 Find the nearest player to the I pawn. 07:25.060 --> 07:31.480 So let's open pts, find nearest player and take a look at our behavior tree service. 07:31.720 --> 07:39.280 Now a behavior tree service as we mentioned, is designed to perform some kind of action at a regular 07:39.280 --> 07:40.210 interval. 07:40.210 --> 07:43.300 In fact our service has an interval parameter. 07:43.300 --> 07:50.380 By default it's set to 0.5 seconds, which means every half second this service will tick. 07:50.380 --> 07:54.340 We can even add a random deviation to the service. 07:54.340 --> 07:58.810 Now our details panel has a couple other things that we'll briefly mention. 07:58.810 --> 08:02.020 One is the node name which we can customize. 08:02.020 --> 08:11.110 I'm just going to fill this in with find nearest player and a custom description which is optional. 08:11.290 --> 08:15.190 We could say finds nearest player if we like. 08:15.190 --> 08:20.650 And we can attach our custom service in our behavior tree to our selector. 08:20.650 --> 08:24.820 We can right click Add Service and there's our Pts. 08:24.820 --> 08:31.090 Find nearest player and notice that its name is just find nearest player because that's what I set it 08:31.090 --> 08:33.070 to for the node name. 08:33.310 --> 08:36.730 So now we have this attached to our selector. 08:36.730 --> 08:43.480 And it's going to tick according to its interval which by the way we can select find nearest player 08:43.480 --> 08:44.950 and change its interval. 08:44.950 --> 08:47.530 It's exposed to the details panel. 08:47.530 --> 08:49.420 I'm going to leave it at 0.5. 08:49.690 --> 08:57.100 And the way we give this ticking functionality is by overriding one of its overridable functions. 08:57.100 --> 09:05.050 We're interested in receive tick I if we choose that we have access to the owner controller, the controlled 09:05.050 --> 09:12.070 pawn, even delta seconds, and we can do something at this services interval. 09:12.070 --> 09:15.280 All I'd like to do for now is do a print string. 09:15.280 --> 09:16.570 We can print hello. 09:16.570 --> 09:22.690 Or we could even get the owner controller call get object name on it if we'd like to print the name 09:22.690 --> 09:24.520 of the owner controller. 09:24.520 --> 09:25.660 Let's see what happens. 09:25.660 --> 09:32.080 If we compile this and go into our game and press play, we can see that tick happening. 09:32.080 --> 09:40.000 And all three of the I pawns are controlled by the controllers that we have printed to the screen there, 09:40.000 --> 09:42.760 and we also have access to the controlled pawn. 09:42.760 --> 09:49.900 We could print the object name for the controlled pawn as well, and just see that those are the corresponding 09:49.900 --> 09:53.290 pawns that control these behavior trees. 09:53.290 --> 09:58.390 So as you can see, we have created our behavior tree service. 09:58.390 --> 10:02.590 We see that these services are ticking for each of our I pawns. 10:02.590 --> 10:05.830 It's quite easy to attach a service to. 10:06.130 --> 10:11.560 One of our selector nodes as we've done, but all we're doing is printing a message to the screen. 10:11.560 --> 10:15.760 What we'd like to do is find the nearest player. 10:15.760 --> 10:21.880 In other words, where's aura, how close is aura, etc. so for that, we'll start setting things up 10:21.880 --> 10:23.350 in the next video. 10:23.380 --> 10:25.270 Great job and I'll see you soon.