1 00:00:04,280 --> 00:00:05,540 ‫Hello and welcome. 2 00:00:05,540 --> 00:00:09,140 ‫In this lecture, we've got our eye that is following us around the world. 3 00:00:09,140 --> 00:00:11,570 ‫It will go and investigate when he loses sight of me. 4 00:00:11,570 --> 00:00:13,730 ‫So it's quite hard to lose. 5 00:00:13,730 --> 00:00:20,120 ‫But if I go too many corners away, he's not going to be able to keep up and eventually he's going to 6 00:00:20,120 --> 00:00:25,160 ‫lose interest and go back to his start location over there. 7 00:00:25,370 --> 00:00:31,010 ‫That's what we're going to be implementing in this lecture by finishing off our behavior tree task. 8 00:00:31,010 --> 00:00:32,930 ‫Let's dive in and see how it's done. 9 00:00:33,550 --> 00:00:38,380 ‫So we want to get our task to execute, to actually do something. 10 00:00:38,380 --> 00:00:42,400 ‫And particularly we want to be able to clear that blackboard value, do what it says on the tin. 11 00:00:42,820 --> 00:00:44,830 ‫So how do we go about doing that? 12 00:00:44,860 --> 00:00:49,210 ‫Well, for that, we need to go up to our base class and have a look at what's implemented there. 13 00:00:49,210 --> 00:00:56,350 ‫In fact, we need to go up one level higher, which, as you can see from the inheritance of the task 14 00:00:56,890 --> 00:00:57,880 ‫blackboard base. 15 00:00:57,880 --> 00:01:00,540 ‫Above that we have the BT task node. 16 00:01:00,550 --> 00:01:05,320 ‫So let's use F 12 to navigate to the implementation there. 17 00:01:05,320 --> 00:01:12,700 ‫And if you scroll up to the top of the BT task node header file, you can see there's the information 18 00:01:12,700 --> 00:01:13,720 ‫about this class. 19 00:01:13,720 --> 00:01:18,670 ‫And the most important thing is that these are the virtual functions that we're most likely to want 20 00:01:18,670 --> 00:01:19,960 ‫to implement. 21 00:01:20,260 --> 00:01:22,510 ‫So the first one is execute task. 22 00:01:22,510 --> 00:01:30,760 ‫This is called when the task starts to execute, we then have a board task, which is when it's decided 23 00:01:30,760 --> 00:01:36,100 ‫that we need to stop executing, for example, because a condition has become false and we've got that 24 00:01:36,100 --> 00:01:37,060 ‫signalling set up. 25 00:01:37,060 --> 00:01:38,710 ‫So it aborts this task. 26 00:01:39,040 --> 00:01:43,720 ‫Tick task happens all the time that the task is executing, but not the first tick. 27 00:01:43,720 --> 00:01:46,660 ‫So the first tick will call execute task thereafter. 28 00:01:46,660 --> 00:01:49,540 ‫We'll keep calling tick task every time. 29 00:01:50,140 --> 00:01:56,200 ‫And that's for behaviors that might run for longer than one tick, such as moving to an enemy might 30 00:01:56,200 --> 00:01:57,400 ‫take multiple ticks. 31 00:01:57,400 --> 00:01:59,710 ‫So tick task allows us to do something. 32 00:01:59,710 --> 00:02:05,290 ‫Every tick and on message is for other things other than aborting that might send a message to this 33 00:02:05,290 --> 00:02:05,860 ‫task. 34 00:02:05,860 --> 00:02:09,250 ‫We don't really have to worry about this particular function. 35 00:02:09,250 --> 00:02:15,370 ‫So the first three are really the ones we're more interested in, and seeing as our task is simply just 36 00:02:15,370 --> 00:02:21,370 ‫going to clear the blackboard value as soon as it is executed and then it's going to finish straightaway. 37 00:02:21,370 --> 00:02:24,100 ‫It doesn't need to do things across multiple ticks. 38 00:02:24,100 --> 00:02:30,190 ‫We're interested in the execute task, so if we search in this header file for execute task, you can 39 00:02:30,190 --> 00:02:37,420 ‫see the full signature is here and the return type here is this boot node result. 40 00:02:38,080 --> 00:02:43,660 ‫And it takes in two things the owner component and the node memory. 41 00:02:43,720 --> 00:02:48,880 ‫Now the reason it takes in node memory is a little bit complicated, but the important thing to know 42 00:02:48,880 --> 00:02:58,930 ‫here is that a task class or a task class instance, there's only one of them per all of the blackboards. 43 00:02:58,930 --> 00:03:04,960 ‫Essentially, they get shared between everything, which is why if you want to save some information 44 00:03:04,960 --> 00:03:12,400 ‫that's related to a node in one particular behavior tree, then what you need to do is store it in this 45 00:03:12,400 --> 00:03:13,660 ‫memory pointer. 46 00:03:13,660 --> 00:03:16,210 ‫But we're not going to be doing anything related to that. 47 00:03:16,210 --> 00:03:18,670 ‫It's a little bit more advanced to need to do that. 48 00:03:18,670 --> 00:03:23,860 ‫And there are other ways to get around this, such as allowing Unreal to create multiple instances for 49 00:03:23,860 --> 00:03:28,450 ‫every behavior tree, which might be a little bit neater or not, but this is a slightly more efficient 50 00:03:28,450 --> 00:03:30,430 ‫way and we don't have to worry about it. 51 00:03:30,430 --> 00:03:35,620 ‫Ultimately, what we're interested in is the fact that we can get to our own a component, the behavior 52 00:03:35,620 --> 00:03:40,930 ‫tree component, and from there we can get to other things such as the pawn, etc. But that's also the 53 00:03:40,930 --> 00:03:43,270 ‫subject of another lecture. 54 00:03:43,270 --> 00:03:48,910 ‫So what's interesting and important now is just to implement our execute task. 55 00:03:48,910 --> 00:03:55,450 ‫So we're going to copy the signature, go over to our clear blackboard value H and let's just see as 56 00:03:55,450 --> 00:04:00,040 ‫this public note, I think this is going to be protected because it's in the default section. 57 00:04:00,040 --> 00:04:04,930 ‫So we're going to create ourselves a protected section and paste it in there and then we're going to 58 00:04:04,930 --> 00:04:08,500 ‫go ahead and create the or put an override just to make sure be safe. 59 00:04:08,500 --> 00:04:14,500 ‫And then we're going to create an implementation over in the C++, remembering that we always want to 60 00:04:14,500 --> 00:04:21,520 ‫be calling to super when we're overriding so super execute task with the owner component and the node 61 00:04:21,520 --> 00:04:24,460 ‫memory being called up to our parent here. 62 00:04:24,460 --> 00:04:30,790 ‫And then what we want to do is get hold of our blackboard so that we can clear the key. 63 00:04:30,790 --> 00:04:32,230 ‫And there's two things that are important here. 64 00:04:32,230 --> 00:04:35,140 ‫First of all, how do we know what Key was selected? 65 00:04:35,140 --> 00:04:41,230 ‫Well, if we go to our Blackboard Base H, you can see that one of the methods there is get selected 66 00:04:41,230 --> 00:04:42,340 ‫Blackboard Key. 67 00:04:42,340 --> 00:04:48,220 ‫So you can easily just call this in your C++, get selected Blackboard Key, and that's going to return. 68 00:04:48,220 --> 00:04:54,100 ‫If we hover over it, it returns an F name, the F name of the blackboard key that was selected in the 69 00:04:54,100 --> 00:04:54,730 ‫behavior tree. 70 00:04:54,730 --> 00:04:59,380 ‫Now, the other thing we need to do is to be actually actually able to get hold of the blackboard related 71 00:04:59,380 --> 00:05:00,280 ‫to this behavior tree. 72 00:05:00,280 --> 00:05:02,380 ‫So for that, we've got our own a comp. 73 00:05:02,380 --> 00:05:07,990 ‫Now notice here that the type of owner comp being passed in here is actually a reference, not a pointer. 74 00:05:07,990 --> 00:05:09,850 ‫So it can't be null for a start. 75 00:05:09,850 --> 00:05:10,720 ‫That's great. 76 00:05:10,720 --> 00:05:15,730 ‫But it also means that we need to use the dot operator rather than the the arrow operator because we're 77 00:05:15,730 --> 00:05:21,910 ‫not using a pointer and from here we can simply get blackboard component. 78 00:05:21,910 --> 00:05:26,260 ‫So that just gets the blackboard component if you hover over it, this one is a pointer to a blackboard 79 00:05:26,260 --> 00:05:29,470 ‫component, so you will need to use arrow operators. 80 00:05:29,470 --> 00:05:32,680 ‫So we already know how to clear keys on blackboard. 81 00:05:32,880 --> 00:05:34,590 ‫Opponents, that's going to be your challenge. 82 00:05:34,590 --> 00:05:36,690 ‫So hopefully the challenge is not too complicated. 83 00:05:36,690 --> 00:05:38,620 ‫You want to clear the selected key. 84 00:05:38,800 --> 00:05:41,730 ‫We you can check where we've done this before. 85 00:05:42,240 --> 00:05:44,910 ‫Do you need any includes in order to do this? 86 00:05:44,910 --> 00:05:53,010 ‫Maybe the blackboard needs to include use the key selected in your behaviour tree as the key that we 87 00:05:53,010 --> 00:05:53,550 ‫want to clear. 88 00:05:53,550 --> 00:05:55,530 ‫So pause the video and have a go. 89 00:05:55,560 --> 00:05:56,670 ‫Okay, welcome back. 90 00:05:56,670 --> 00:05:58,740 ‫So let's give this a shot. 91 00:05:58,740 --> 00:06:01,560 ‫So the first thing is we've got our blackboard component. 92 00:06:01,560 --> 00:06:03,060 ‫Let's use the error operator here. 93 00:06:03,360 --> 00:06:04,560 ‫Nothing is coming up. 94 00:06:04,560 --> 00:06:11,910 ‫So I'm assuming that I need and indeed there's some red squiggles I need a hash include here to do the 95 00:06:11,910 --> 00:06:15,960 ‫behavior tree and then the blackboard component here and now. 96 00:06:15,960 --> 00:06:21,300 ‫Hopefully my autocomplete should be working, which will allow me to have the clear. 97 00:06:21,300 --> 00:06:23,580 ‫Let's just try and refresh our memories. 98 00:06:23,580 --> 00:06:25,230 ‫Where have we done this before? 99 00:06:25,230 --> 00:06:30,810 ‫If we go over to Shooter I, Controller CP and have a look at what we've got here, we've got clear 100 00:06:30,810 --> 00:06:31,500 ‫value. 101 00:06:31,500 --> 00:06:32,790 ‫That's the one we're looking for. 102 00:06:32,790 --> 00:06:35,430 ‫So let's try that clear value. 103 00:06:35,430 --> 00:06:36,600 ‫And what does it take in? 104 00:06:36,600 --> 00:06:41,370 ‫It takes in either an F key or an F name, great f name we can get. 105 00:06:41,370 --> 00:06:46,830 ‫And where did we say we could get that with the get selected blackboard key that is on this class because 106 00:06:46,830 --> 00:06:48,030 ‫it's in the parent class. 107 00:06:48,030 --> 00:06:51,300 ‫So get selected Blackboard Key and it's as simple as that. 108 00:06:51,300 --> 00:06:53,910 ‫We're clearing the value of the selected Blackboard Key. 109 00:06:53,910 --> 00:06:55,590 ‫Now, one final thing we need to do. 110 00:06:55,590 --> 00:06:57,060 ‫This wasn't part of your challenge, so don't worry. 111 00:06:57,060 --> 00:07:03,240 ‫If you didn't know this is that we need to return because there is a return value for our clear blackboard 112 00:07:03,240 --> 00:07:04,680 ‫value execute task. 113 00:07:04,680 --> 00:07:06,810 ‫And the return value is quite interesting. 114 00:07:06,810 --> 00:07:07,410 ‫Let's have a look. 115 00:07:07,410 --> 00:07:12,600 ‫Let's follow it with an F 12 and see what different status is we can return from our execute test. 116 00:07:12,600 --> 00:07:14,400 ‫Now the first one is succeeded. 117 00:07:14,400 --> 00:07:14,760 ‫Great. 118 00:07:14,760 --> 00:07:19,710 ‫That basically signals to the behaviour tree that this node is finished executing and we can move on 119 00:07:19,710 --> 00:07:20,910 ‫to the next one. 120 00:07:20,910 --> 00:07:21,930 ‫Failed again. 121 00:07:21,930 --> 00:07:27,450 ‫This is a finished so we can move on to the next one, but this time it's saying that it failed. 122 00:07:27,450 --> 00:07:34,500 ‫So that gives the different indications to, for example, as sequence nodes or our selected nodes as 123 00:07:34,500 --> 00:07:36,750 ‫to what those nodes should actually be doing. 124 00:07:37,260 --> 00:07:44,850 ‫Then we have got aborted, which is basically the same as failure and we have in progress. 125 00:07:44,850 --> 00:07:51,420 ‫If you return in progress from an execute task, it's basically going to say you've got to keep calling 126 00:07:51,420 --> 00:07:57,120 ‫tick until I tell you otherwise, until I say that I have finished now we're not going to be using this. 127 00:07:57,120 --> 00:08:02,700 ‫But it's good to keep in mind that if you need to create a task that is long running, we'll run across 128 00:08:02,700 --> 00:08:03,660 ‫multiple ticks. 129 00:08:03,660 --> 00:08:06,060 ‫Then we're going to have to return in progress. 130 00:08:06,060 --> 00:08:08,220 ‫But as I said, we want succeeded. 131 00:08:08,400 --> 00:08:10,260 ‫So let's go in and do that. 132 00:08:10,260 --> 00:08:14,490 ‫Return EB Beat node result colon, colon. 133 00:08:14,490 --> 00:08:20,550 ‫And it is going to be succeeded because we succeeded to clear that value basically no matter what. 134 00:08:20,760 --> 00:08:25,470 ‫So we can go ahead and save all of this, go over into the editor and hit compile. 135 00:08:25,470 --> 00:08:31,710 ‫And when that's complete, let's go ahead and open up our AI and the behavior tree. 136 00:08:31,740 --> 00:08:33,020 ‫So where's that one beat? 137 00:08:33,030 --> 00:08:35,490 ‫And I dock it to the main window and let's have a look. 138 00:08:35,490 --> 00:08:40,800 ‫We've got a clear blackboard value which should now be able to allow us to move to the last known location, 139 00:08:40,800 --> 00:08:47,250 ‫clear the blackboard value, wait for five, and then we should see that investigating this last known 140 00:08:47,250 --> 00:08:52,200 ‫player location should be unset, so we should move back to our start location. 141 00:08:52,200 --> 00:08:56,790 ‫So let's see if this behavior is now working now that the task is fully implement. 142 00:08:56,800 --> 00:09:00,450 ‫So he's coming over to me, he's investigating me. 143 00:09:00,480 --> 00:09:01,800 ‫I'm going to go and hide. 144 00:09:01,800 --> 00:09:03,000 ‫So let's go and hide. 145 00:09:03,150 --> 00:09:04,200 ‫He's coming to investigate. 146 00:09:04,200 --> 00:09:05,550 ‫Let's go and hide again. 147 00:09:05,760 --> 00:09:07,290 ‫So go and hide. 148 00:09:07,830 --> 00:09:10,080 ‫Let's see if we can spot him over there. 149 00:09:10,080 --> 00:09:16,020 ‫He should be waiting at the moment and then he's going back to his start location, which unfortunately 150 00:09:16,020 --> 00:09:18,420 ‫makes him intersect with me. 151 00:09:18,420 --> 00:09:25,350 ‫So let's see if this is actually working as we expect, by bringing out our enemy a window and docking 152 00:09:25,350 --> 00:09:29,820 ‫it over to the right and putting our main window over on the left. 153 00:09:29,820 --> 00:09:34,890 ‫It's a little bit cramped, but we can we can make do and then we're going to try and escape this guy 154 00:09:34,890 --> 00:09:37,800 ‫one more time and see what happens with his behavior. 155 00:09:37,800 --> 00:09:41,910 ‫You can see he is moving to the last known player location. 156 00:09:42,510 --> 00:09:45,990 ‫And now he is waiting, having cleared the value. 157 00:09:45,990 --> 00:09:51,360 ‫And then you can see he's going to move to and you can see these red bars on the decorators are telling 158 00:09:51,360 --> 00:09:54,030 ‫us that neither of these two conditions are true. 159 00:09:54,030 --> 00:09:55,950 ‫So he can't do either of those. 160 00:09:55,950 --> 00:09:57,840 ‫Finally, he's moved to the start location. 161 00:09:57,840 --> 00:10:01,170 ‫So now it's flickering because basically it can't do anything. 162 00:10:01,320 --> 00:10:09,810 ‫So that basically is that this lecture we've seen how we can get the tasks to execute code understood 163 00:10:09,810 --> 00:10:14,910 ‫the different statuses that you can return from execute task how to get the blackboard from the task 164 00:10:14,910 --> 00:10:19,890 ‫and also how to get the currently selected key on a blackboard task. 165 00:10:19,890 --> 00:10:26,310 ‫In the next lecture, we're going to see how we can get hold of the world outside of the blackboard 166 00:10:26,310 --> 00:10:30,450 ‫behavior tree, how we can get hold of the pawn from within a behavior tree task. 167 00:10:30,450 --> 00:10:31,080 ‫I'll see you there.