1 00:00:04,310 --> 00:00:05,240 ‫Hello and welcome. 2 00:00:05,240 --> 00:00:11,660 ‫In this lecture, we're introducing two new types of asset the behavior tree and the blackboard, which 3 00:00:11,660 --> 00:00:16,640 ‫are two assets that allow us to do very interesting things with A.I.. 4 00:00:16,640 --> 00:00:18,740 ‫Allow us to make much more complicated. 5 00:00:18,740 --> 00:00:23,600 ‫I very easily let's dive in and see how we use them and set them up. 6 00:00:25,140 --> 00:00:25,410 ‫Okay. 7 00:00:25,410 --> 00:00:28,970 ‫So we want to create some sophisticated AI behavior. 8 00:00:28,980 --> 00:00:33,960 ‫Now, the way we typically do this in Unreal is using a system called behavior trees. 9 00:00:33,990 --> 00:00:35,050 ‫Now, what are these? 10 00:00:35,070 --> 00:00:38,990 ‫Well, the best way for us to find out is to create one. 11 00:00:39,000 --> 00:00:41,970 ‫So let's go ahead and right click and go. 12 00:00:41,970 --> 00:00:45,150 ‫We're looking here under the artificial intelligence. 13 00:00:45,150 --> 00:00:48,450 ‫And there's two options here behavior, tree and blackboard. 14 00:00:48,480 --> 00:00:51,050 ‫We are going to want both of these. 15 00:00:51,060 --> 00:00:54,650 ‫So let's go and start with the behavior tree. 16 00:00:54,660 --> 00:00:59,670 ‫The prefix for this is BHT and we're going to call this the enemy. 17 00:00:59,670 --> 00:01:01,320 ‫So behavior tree enemy. 18 00:01:01,350 --> 00:01:03,780 ‫I just finish off with that. 19 00:01:03,780 --> 00:01:04,490 ‫There you go. 20 00:01:04,500 --> 00:01:09,180 ‫And we also need to create the other thing in there, which was a blackboard. 21 00:01:09,180 --> 00:01:11,250 ‫Now, what on earth is a blackboard? 22 00:01:11,250 --> 00:01:12,300 ‫We'll get to that in just a second. 23 00:01:12,300 --> 00:01:15,930 ‫But we're just going to call it the b b underscore enemy. 24 00:01:15,940 --> 00:01:19,110 ‫I said before, blackboard beat for behavior tree. 25 00:01:19,110 --> 00:01:22,320 ‫And while we're at it, we've got a few things relating to I here. 26 00:01:22,320 --> 00:01:29,100 ‫I'm going to create a new folder called A.I. and we are going to move the blackboard, the behavior 27 00:01:29,100 --> 00:01:29,640 ‫tree. 28 00:01:29,700 --> 00:01:33,900 ‫And somewhere here we have got our shooter, AI controller. 29 00:01:33,900 --> 00:01:40,530 ‫All of that goes into I move here and then we can go into our AI folder to deal with everything AI related. 30 00:01:41,070 --> 00:01:45,450 ‫Let's open up our behavior tree first of all and dock it to the main window. 31 00:01:45,660 --> 00:01:47,550 ‫So what on earth is this? 32 00:01:47,550 --> 00:01:52,890 ‫So this allows us to create trees of behaviors where you might say we've got part of the behavior here 33 00:01:52,890 --> 00:01:53,880 ‫is for tracing. 34 00:01:53,880 --> 00:01:55,350 ‫Part of it is for trolling. 35 00:01:55,350 --> 00:02:00,180 ‫Part of it is for something else, opening doors, all these kinds of things. 36 00:02:00,180 --> 00:02:06,480 ‫They typically structure behaviors as lots and lots of trees of behaviors and sub trees and so on. 37 00:02:06,480 --> 00:02:14,070 ‫We will see that all going on in detail, but suffice to say it is a great way of putting together natural 38 00:02:14,070 --> 00:02:15,780 ‫behaviors in your games. 39 00:02:16,080 --> 00:02:17,610 ‫Now it's not the be all and end all. 40 00:02:17,610 --> 00:02:19,440 ‫There's lots of AI techniques. 41 00:02:19,440 --> 00:02:23,820 ‫This might not be the one that you want to go with for your game, but it's a great start and you can 42 00:02:23,820 --> 00:02:26,040 ‫achieve quite a lot with it. 43 00:02:26,520 --> 00:02:30,620 ‫Now the next thing we can see over in the top, right, these two assets are linked. 44 00:02:30,630 --> 00:02:33,000 ‫The behavior tree and the blackboard. 45 00:02:33,000 --> 00:02:35,100 ‫What on earth is a blackboard? 46 00:02:35,100 --> 00:02:41,520 ‫Well, the blackboard is kind of like the memory of your A.I. It's essentially where you store a bunch 47 00:02:41,520 --> 00:02:42,240 ‫of variables. 48 00:02:42,240 --> 00:02:46,650 ‫You input them from the gameplay very much like we were doing with the animation system where you had 49 00:02:46,650 --> 00:02:51,150 ‫these these different properties that are being set by the gameplay. 50 00:02:51,150 --> 00:02:53,820 ‫We do the same thing with the AI. 51 00:02:53,850 --> 00:03:00,180 ‫We set lots of properties that give it information about its game world and then the behavior tree draws 52 00:03:00,180 --> 00:03:03,540 ‫on those properties and uses them to decide what it's going to do. 53 00:03:03,540 --> 00:03:09,510 ‫It can set those properties, it can use them as a memory, it can read from those properties and all 54 00:03:09,540 --> 00:03:10,680 ‫that lovely stuff. 55 00:03:10,680 --> 00:03:17,040 ‫So with that in mind, how can we set up our behavior tree in blackboard so that they are linked to 56 00:03:17,040 --> 00:03:17,790 ‫one another? 57 00:03:18,030 --> 00:03:20,460 ‫Well, we're going to expand out in our details pane. 58 00:03:20,460 --> 00:03:26,010 ‫You can see here that there is this blackboard asset and automatically it seems to have filled it out 59 00:03:26,010 --> 00:03:32,790 ‫for us such that the blackboard asset is linked to this b b b enemy I blackboard asset. 60 00:03:33,000 --> 00:03:38,730 ‫Now we are going to be departing from C++ for a little bit to use these assets because obviously behavior 61 00:03:38,730 --> 00:03:42,420 ‫trees and blackboards are entirely within the editor. 62 00:03:42,420 --> 00:03:44,460 ‫They're not blueprints as such. 63 00:03:44,460 --> 00:03:49,320 ‫They are their own editor tools and we can interface with them in C++. 64 00:03:49,320 --> 00:03:53,580 ‫But it does mean we're going to be using the editor for the next couple of lectures as well as C++. 65 00:03:53,580 --> 00:03:54,960 ‫Not so much blueprint though. 66 00:03:54,960 --> 00:04:00,810 ‫So it's great that we've got ourselves this behavior tree and this blackboard, but how on earth do 67 00:04:00,810 --> 00:04:02,400 ‫we actually use it? 68 00:04:02,400 --> 00:04:05,580 ‫Well, for that, we go back to our AI controller. 69 00:04:05,580 --> 00:04:14,040 ‫I if you remember, I controller is entirely responsible for running our behaviors and that is no exception 70 00:04:14,040 --> 00:04:14,640 ‫here. 71 00:04:14,820 --> 00:04:19,110 ‫The behavior tree is just another thing that the AI controller can use or run. 72 00:04:19,260 --> 00:04:24,810 ‫So the way we're going to do this is we're going to go over to our AI control and we need to have a 73 00:04:24,810 --> 00:04:30,090 ‫way of referencing in the blueprint what behavior tree we want it to run. 74 00:04:30,600 --> 00:04:35,130 ‫So the first thing I'm going to do is I'm actually going to go over to the control CP and comment out 75 00:04:35,130 --> 00:04:40,950 ‫the stuff in TTIC because we're going to be replacing this functionality with behavior tree functionality 76 00:04:40,950 --> 00:04:41,640 ‫instead. 77 00:04:41,760 --> 00:04:46,440 ‫And then that means that I can remove this acceptance radius here because we no longer need it. 78 00:04:46,440 --> 00:04:51,180 ‫And instead we're going to be using a pointer to the new behavior. 79 00:04:51,780 --> 00:04:59,100 ‫And I have to spell this The American Way Tree and pointer, that's the behavior tree we want there. 80 00:04:59,100 --> 00:05:02,310 ‫And I need to forward declare this with a class in front of it. 81 00:05:02,310 --> 00:05:08,910 ‫And then basically here, what I want to say is that this is the AI behavior and. 82 00:05:09,770 --> 00:05:13,340 ‫I'm going to keep the American spelling here just for consistency. 83 00:05:13,340 --> 00:05:17,630 ‫So this is the AI behavior that we want here now to actually run the behavior. 84 00:05:17,630 --> 00:05:18,560 ‫It couldn't be simpler. 85 00:05:18,560 --> 00:05:22,700 ‫Again, the eye control has a built in function for this. 86 00:05:22,700 --> 00:05:24,500 ‫We've got this run behavior. 87 00:05:24,500 --> 00:05:26,390 ‫Tree function turns a boolean. 88 00:05:26,390 --> 00:05:30,650 ‫Whether you are able to successfully execute it or not, start executing it, that is. 89 00:05:30,650 --> 00:05:35,930 ‫And it takes in the beat asset which is appointed to the new behavior tree. 90 00:05:36,290 --> 00:05:40,040 ‫So that's what we're going to want to use and we can do this over in begin play. 91 00:05:40,040 --> 00:05:44,270 ‫So what we're going to do is, first of all, we're going to check that we indeed have a behavior tree 92 00:05:44,300 --> 00:05:44,660 ‫here. 93 00:05:44,660 --> 00:05:47,210 ‫So we're going to say I behavior. 94 00:05:48,270 --> 00:05:53,640 ‫Is not equal to null pointer because we do not want to be using it otherwise. 95 00:05:53,640 --> 00:05:59,130 ‫And then what we can do is we can run the behavior tree called our AI behavior. 96 00:05:59,160 --> 00:06:06,420 ‫It really is that simple to get an AI behavior running and we can go ahead and compile. 97 00:06:07,420 --> 00:06:12,790 ‫And one more thing we can do with behavior trees is we can kind of see them running at runtime, but 98 00:06:12,790 --> 00:06:15,150 ‫to do that, you need to have some sort of node in here. 99 00:06:15,160 --> 00:06:18,910 ‫So we're just going to add in a node without fully understanding what it does. 100 00:06:18,910 --> 00:06:23,830 ‫I'm going to add in a sequence node and I'm going to hook it up by dragging down from the root node, 101 00:06:23,830 --> 00:06:28,780 ‫the bit underneath the root node that highlights when I mouse over it down to the bit above the sequence 102 00:06:28,780 --> 00:06:29,350 ‫node. 103 00:06:29,440 --> 00:06:30,850 ‫And I'm going to save that. 104 00:06:31,240 --> 00:06:39,700 ‫I'm going to go over and hit play and go into my behavior tree asset and you should be able to see a 105 00:06:39,700 --> 00:06:43,420 ‫dropdown here, but we're not because it's not currently running. 106 00:06:43,420 --> 00:06:44,530 ‫So let's stop playing. 107 00:06:45,010 --> 00:06:46,660 ‫And why is it not running? 108 00:06:46,660 --> 00:06:49,360 ‫Because we haven't hooked it up in our shooter controller. 109 00:06:49,360 --> 00:06:52,840 ‫So let's do that mini challenge for you to hook that up. 110 00:06:53,110 --> 00:06:54,610 ‫Hopefully it shouldn't be too hard. 111 00:06:55,060 --> 00:06:56,170 ‫Okay, welcome back. 112 00:06:56,170 --> 00:07:01,330 ‫So if we go and have a look in here, we're looking for our AI behavior. 113 00:07:01,510 --> 00:07:04,300 ‫For some reason, it required a recompile for me to show up for me. 114 00:07:04,300 --> 00:07:04,930 ‫But here it is. 115 00:07:04,930 --> 00:07:06,760 ‫AI behavior is what we want. 116 00:07:06,790 --> 00:07:07,780 ‫We click the drop down. 117 00:07:07,780 --> 00:07:10,630 ‫There's only one option at the moment because we've only got one behavior tree. 118 00:07:10,630 --> 00:07:14,200 ‫So let's select that one and compile and save. 119 00:07:14,200 --> 00:07:17,380 ‫And if we now go ahead and play the game. 120 00:07:18,010 --> 00:07:20,830 ‫And go and have a look at our beat enemy. 121 00:07:21,280 --> 00:07:26,140 ‫You can see that it's highlighting the node that's currently running and you've got this little drop 122 00:07:26,140 --> 00:07:32,350 ‫down next to the pause stop buttons, which tells you which I controller you're currently observing 123 00:07:32,350 --> 00:07:33,130 ‫the behavior tree of. 124 00:07:33,160 --> 00:07:38,350 ‫So this is a great functionality for you to be able to jump in and go, okay, why is that? 125 00:07:38,350 --> 00:07:39,760 ‫I just standing still. 126 00:07:39,760 --> 00:07:41,290 ‫Why is he not chasing the player? 127 00:07:41,290 --> 00:07:46,510 ‫You can see which part of the behavior he's currently running and go, Ah, that c you know, that thing's 128 00:07:46,510 --> 00:07:47,110 ‫gone wrong. 129 00:07:47,140 --> 00:07:48,910 ‫It's really helpful for debugging. 130 00:07:48,910 --> 00:07:53,890 ‫You can go and have a look at what all your AI in the world are up to by using this dropdown. 131 00:07:54,010 --> 00:07:54,550 ‫Great stuff. 132 00:07:54,550 --> 00:07:55,570 ‫That's all for this lecture. 133 00:07:55,570 --> 00:08:01,930 ‫In the next lecture, we're going to be looking at how we can set information in the blackboard memory 134 00:08:01,930 --> 00:08:04,600 ‫of our AI from C++. 135 00:08:04,600 --> 00:08:05,560 ‫I'll see you there.