WEBVTT 00:06.880 --> 00:08.020 Welcome back. 00:08.020 --> 00:14.140 Now our find nearest player algorithm is ready to be created by us. 00:14.140 --> 00:18.550 We have all actors with the target tag for our goblins. 00:18.550 --> 00:20.080 That's going to be the player tag. 00:20.080 --> 00:23.110 And there may be more than one aura in the game. 00:23.110 --> 00:33.220 Or if the owning AI being driven by this behavior tree is perhaps a pet following aura around, well, 00:33.220 --> 00:38.980 then it's going to have the player tag and its array of actors will contain the enemy tag. 00:39.010 --> 00:45.970 Either way, this array could have multiple actors, and we want to find the closest of the actors. 00:45.970 --> 00:53.140 So we're going to implement a pretty standard distance checking algorithm to find the closest actor. 00:53.500 --> 00:58.090 This could be a problem that you're given in a programming interview, for instance. 00:58.090 --> 01:00.880 So let's see how we're going to implement this. 01:00.880 --> 01:06.340 For one, why don't we just go ahead and collapse this to a function right away? 01:06.340 --> 01:08.170 So collapse the function. 01:08.170 --> 01:11.890 We'll call this find nearest player. 01:11.890 --> 01:20.290 And here in find nearest player we can simply loop over the actors with tag. 01:20.410 --> 01:24.730 And I'm going to add a couple of local variables here. 01:24.730 --> 01:30.370 One for the closest actor that's going to be a variable of type actor. 01:30.370 --> 01:33.190 So we'll call this closest actor. 01:33.190 --> 01:36.010 We'll set its type to actor object Reference. 01:36.010 --> 01:42.880 And in the beginning here we're going to set closest actor to an empty reference in C plus. 01:42.880 --> 01:45.010 Plus this would be setting it to null. 01:45.010 --> 01:47.830 So first we clear out closest actor. 01:47.830 --> 01:52.900 And we're also going to have another variable for the closest distance. 01:52.900 --> 01:56.530 So this one will be called closest distance. 01:56.530 --> 01:58.660 And its type can be float. 01:58.660 --> 02:04.630 And we're going to set its value to a very large value from the start. 02:04.780 --> 02:09.760 So we can just enter a whole bunch of nines in here if we want to. 02:09.760 --> 02:11.740 Just a large number. 02:11.740 --> 02:16.630 And of course float doesn't accommodate for that many digits. 02:16.630 --> 02:21.580 So we'll just go ahead and put a large, large number here. 02:21.580 --> 02:27.280 Now the reason we want a large number is because we're going to loop through the array and compare each 02:27.280 --> 02:33.160 element's distance to the owning pawn to this closest distance. 02:33.160 --> 02:39.670 And the first time that distance is going to be less than the value in closest distance. 02:39.670 --> 02:47.080 And then each subsequent actor we check may or may not be closer, but by the end we'll have the closest 02:47.080 --> 02:47.500 one. 02:47.500 --> 02:49.030 So here's how we're going to do it. 02:49.030 --> 02:53.410 First, I'd like to just pass in that controlled pawn. 02:53.440 --> 02:57.820 The one that we have access to here in event receive tick. 02:57.820 --> 03:00.970 I so find nearest player can get an input. 03:00.970 --> 03:03.190 And we'll call this owning pawn. 03:03.340 --> 03:07.780 And we'll set its type to pawn object reference. 03:07.780 --> 03:10.630 And we'll pass that controlled pawn straight in. 03:10.630 --> 03:13.090 In fact I want it to be called controlled pawn. 03:13.090 --> 03:14.350 So I'll change that. 03:16.690 --> 03:21.130 So now find nearest player has controlled pawn which we can access here. 03:21.130 --> 03:24.730 And I'd like to do so here in the for each loop. 03:24.730 --> 03:28.360 So the first thing I'll do is take the array element. 03:28.360 --> 03:30.220 We'll check is valid. 03:30.880 --> 03:35.500 Make sure we're not trying to access something that is not valid. 03:35.500 --> 03:42.580 And we'll also take our owning pawn here the controlled pawn and see if that's valid as well. 03:42.580 --> 03:44.650 So I'm going to search for controlled pawn. 03:44.650 --> 03:49.360 And if you didn't know controlled pawn is an input parameter here to this function. 03:49.360 --> 03:53.170 Therefore I can get a get node by searching for it. 03:53.170 --> 03:56.200 We don't have to create a local variable for it. 03:56.200 --> 04:02.500 I'm going to check if this one is valid as well, and if they're both valid, well then I can calculate 04:02.500 --> 04:04.180 the distance between them. 04:05.160 --> 04:07.980 So I'm going to first take the controlled pawn. 04:09.660 --> 04:12.000 I'm going to call get Distance2. 04:12.550 --> 04:15.010 And pass in the array element. 04:15.040 --> 04:21.880 This will give us the distance between the controlled pawn and the array element, which is an actor 04:21.880 --> 04:22.900 and the array. 04:22.930 --> 04:29.350 Now I'm going to check to see if this distance is less than closest distance, and the first time it 04:29.350 --> 04:30.070 will be. 04:30.070 --> 04:35.950 So we're going to use a less than operator checking against closest distance. 04:35.950 --> 04:38.560 So we'll have a branch like so. 04:38.560 --> 04:46.150 And if this is true then we found an actor that's closer than our closest distance. 04:46.150 --> 04:51.850 And in this case we're going to set closest distance to this distance we've calculated. 04:51.850 --> 04:55.510 So the get distance two we can hook that up here. 04:56.080 --> 04:57.190 It looks a little ugly. 04:57.190 --> 04:59.710 So I'm going to promote it to a local variable. 05:00.190 --> 05:04.120 We'll call this calculated distance. 05:04.120 --> 05:05.920 And we'll set that here. 05:05.920 --> 05:08.950 And we'll use that for closest distance. 05:08.950 --> 05:15.760 And to avoid this I'm going to pass calculated distance the set node in here. 05:15.760 --> 05:18.760 So it looks a little bit more clear what we're doing. 05:20.080 --> 05:24.880 Now, in addition to setting the closest distance, I also want to set the closest actor. 05:24.880 --> 05:26.890 So we're going to get a set node for that. 05:26.890 --> 05:35.230 And we're going to pass in the array element, which I would also like a local variable for. 05:35.470 --> 05:43.570 So I'm going to move these forward just a bit and promote the array element to a local variable called 05:43.570 --> 05:44.620 actor. 05:48.740 --> 05:50.480 This will be what we check in. 05:50.480 --> 05:51.770 The is valid. 05:52.100 --> 05:57.380 It will also be what we get the distance to here already. 05:57.380 --> 06:01.490 That's looking better and it will be what we set. 06:01.490 --> 06:04.070 Closest actor to here. 06:04.730 --> 06:11.990 So by the end of this loop, by the time we hit our completed, we will have the closest actor and the 06:11.990 --> 06:13.190 closest distance. 06:13.190 --> 06:17.210 And we can then set our blackboard key selectors. 06:17.210 --> 06:27.020 If we right click and search for set blackboard value as we can set a blackboard value as object. 06:27.020 --> 06:30.950 If we select that this function expects a key. 06:30.950 --> 06:35.120 And we have a key for target to follow, we can pass that in. 06:35.120 --> 06:37.160 We'll hook this up to completed. 06:37.430 --> 06:44.420 And we have to set this to an object that's going to be the closest actor that we've found. 06:44.420 --> 06:54.470 We'll also use set blackboard value but this time as float because we have another one for the distance 06:54.470 --> 06:55.430 to target. 06:55.880 --> 06:57.980 So we'll pass that in. 06:59.070 --> 07:00.960 Just making room here. 07:01.540 --> 07:04.030 We'll pass in distance to target. 07:05.580 --> 07:13.320 And we'll pass in the closest distance which we've calculated not calculated distance, just closest 07:13.320 --> 07:13.950 distance. 07:13.950 --> 07:18.210 So by the end of the loop these blackboard keys will be set. 07:18.210 --> 07:24.240 Now we need to make the link between these two selectors and our blackboard keys. 07:24.240 --> 07:28.140 To do that we open the I icon for both of them. 07:28.140 --> 07:32.850 Compile and go back to our blueprint and select Find Nearest Player. 07:32.850 --> 07:38.040 And now we can make the link here because our selectors are now instance editable. 07:38.040 --> 07:40.050 They're exposed to the details panel. 07:40.050 --> 07:46.710 And we can link them up by setting them here to our target to follow and our distance to target blackboard 07:46.710 --> 07:47.490 keys. 07:47.490 --> 07:50.040 So we'll do that here with the dropdown target. 07:50.040 --> 07:56.730 To follow selector we'll get target to follow distance to target selector will get distance to target. 07:56.730 --> 08:02.460 And now when we set them in our service they will be set on our blackboard. 08:02.460 --> 08:10.200 So now that we have our target to follow and distance to target blackboard keys being set at this interval, 08:10.200 --> 08:12.900 we can use them in our behavior tree. 08:12.900 --> 08:17.460 For instance, we can drag off of our selector and we can get a task. 08:17.460 --> 08:24.690 Let's try getting a move to and our move two if we select it has a blackboard key for its target. 08:24.870 --> 08:27.930 Let's say we set that to target to follow. 08:28.290 --> 08:31.410 Well what do you expect to happen if we play test. 08:31.410 --> 08:32.820 Let's check it out. 08:32.820 --> 08:34.350 We can press play. 08:34.470 --> 08:37.020 And look they're following aura. 08:38.340 --> 08:44.910 That's because every second, well, every half second, rather they're finding the nearest player and 08:44.910 --> 08:46.800 move to is being executed. 08:46.800 --> 08:52.860 So this is really powerful that we can have a service run at a specific interval. 08:53.250 --> 08:55.710 It's not run every frame of the game. 08:55.710 --> 09:01.500 It's run every 0.4 seconds with a random deviation, which is much more performant. 09:01.500 --> 09:06.420 And this is why behavior tree services are so useful. 09:06.510 --> 09:10.140 Excellent job and I'll see you in the next video.