WEBVTT 00:06.850 --> 00:07.750 Welcome. 00:07.750 --> 00:13.120 Now, being a top down game will be wanting to click on enemies to attack them. 00:13.120 --> 00:19.260 It would be nice if we could have some sort of highlight effect to show us which enemy is being targeted 00:19.270 --> 00:19.750 Now. 00:19.750 --> 00:25.540 The player controller class has ways to see what's beneath the mouse cursor, so this is a great class 00:25.540 --> 00:26.770 to handle this in. 00:26.800 --> 00:33.910 Now let's say that we have a goblin spear in the world and we hover over it with our mouse cursor. 00:33.910 --> 00:38.860 What we want is for that enemy to be highlighted with some sort of red outline. 00:38.860 --> 00:46.540 But if we hover over another enemy of another type, say a goblin slingshot, we want that enemy to 00:46.540 --> 00:47.440 highlight. 00:47.440 --> 00:54.280 Now, we could get the actor under our mouse cursor and say, cast it to one of these classes and highlight 00:54.280 --> 00:57.040 that actor if it's of the correct type. 00:57.040 --> 01:02.020 In fact, these enemies share the same parent class, the ora enemy class. 01:02.020 --> 01:08.690 So we could cast to that, but that limits us to only being able to highlight objects that derive from 01:08.690 --> 01:09.800 that class. 01:10.040 --> 01:16.040 On top of that, it makes the Ora player controller class dependent on the Ora enemy class. 01:16.040 --> 01:18.950 And we'd like our code to be more versatile than that. 01:18.980 --> 01:23.030 To achieve this versatility, we can create an interface class. 01:23.030 --> 01:27.950 Now the name isn't all that important, but I'll call this the enemy interface class. 01:27.950 --> 01:33.170 And when hovering over an actor, we can check to see if it implements this interface. 01:33.170 --> 01:37.310 If it does, we can then call an interface function on that interface. 01:37.310 --> 01:43.430 This gives us more flexibility because the Ora player controller doesn't need to know what should happen 01:43.430 --> 01:45.830 to an actor when hovering over it. 01:45.860 --> 01:51.560 All it knows is that if the actor implements the interface, it should call that interface function 01:51.560 --> 01:57.020 and the actor can override that function and implement it in any way it wants. 01:57.050 --> 02:01.340 Different enemy classes can have different functionality for the highlight function. 02:01.340 --> 02:06.770 We could add this interface to a barrel or a door and handle highlighting those objects differently. 02:06.770 --> 02:08.540 If we wanted to do that. 02:08.540 --> 02:14.330 In that case, the name enemy interface might be less appropriate for the name and it might be better 02:14.330 --> 02:18.350 to call it something else like target interface or highlight interface. 02:18.350 --> 02:25.160 But either way, an interface is the way to go if we'd like this type of versatility, and this is what 02:25.190 --> 02:28.820 experienced developers call good coding practice. 02:28.820 --> 02:30.650 So let's make our interface. 02:30.650 --> 02:32.480 So we'd like to make an interface. 02:32.480 --> 02:38.870 I'm going to go into my C plus plus classes folder into Ora public and I'll make the class here. 02:39.200 --> 02:43.730 And if I scroll all the way down to the bottom, we have unreal interface. 02:43.730 --> 02:48.110 We're going to use that and I'd like to keep my interface in its own folder. 02:48.110 --> 02:54.800 I'm going to call this folder interaction and I'll place this interface here and I'm going to call this 02:54.800 --> 02:58.250 enemy interface so I can create the class. 02:58.250 --> 03:04.340 I'm going to click No and go ahead and close the editor so I can now have my interface here and here 03:04.340 --> 03:06.370 it pops up in interaction. 03:06.380 --> 03:08.930 Here's enemy interface Dot H. 03:09.230 --> 03:16.010 Now enemy interface is going to have a couple of functions I'd like to call a function that will allow 03:16.040 --> 03:19.550 me to highlight the enemy when we hover over it. 03:19.550 --> 03:27.830 So I'm going to make a virtual function here, virtual void, and I'll call this simply highlight actor. 03:28.670 --> 03:36.800 Now, if I place an equals zero here, then this will now be a pure virtual function, which means that 03:36.800 --> 03:40.400 we will not provide a definition here in this class. 03:40.400 --> 03:45.800 This class is now considered abstract and must be derived from. 03:45.800 --> 03:49.730 That's how we're going to implement this interface in the enemy class. 03:49.730 --> 03:57.410 And any class that implements this interface will be required to override this pure virtual function 03:57.410 --> 03:59.450 and provide a definition for it. 03:59.510 --> 04:08.330 I'm going to make another one virtual void and call this Unhighlight actor and I'll make that also pure 04:08.360 --> 04:09.170 virtual. 04:09.170 --> 04:15.950 And that way we'll have two interface functions that we can call to highlight and unhighlight any actor 04:15.950 --> 04:17.600 that implements this interface. 04:17.750 --> 04:21.200 So let's implement this on the enemy. 04:21.200 --> 04:27.920 I'd like the Ora enemy class to implement it, so I'm going to go to Ora Enemy dot H and right here 04:27.920 --> 04:29.720 is where I can inherit. 04:29.720 --> 04:39.080 From this class I'm going to say public I enemy interface and remember the include for enemy interface 04:39.080 --> 04:44.870 must be here in the header file if we're going to inherit from that interface. 04:44.870 --> 04:48.890 Class writer just popped it up there for me automatically. 04:48.920 --> 04:56.030 Visual Studio won't do that, so you'll need to include the header file for this class now, because 04:56.030 --> 05:03.080 we're implementing this interface now, the Ora enemy class must override those pure virtual functions. 05:03.170 --> 05:05.150 I'm going to show you what happens if we don't do that. 05:05.150 --> 05:06.440 I'm going to go ahead and. 05:06.680 --> 05:07.460 Pile. 05:08.990 --> 05:10.700 Let's see what errors we get. 05:10.730 --> 05:12.440 Now here's what we get. 05:12.470 --> 05:16.040 Ora enemy cannot instantiate abstract class. 05:16.070 --> 05:23.630 Remember, as soon as we added a pure virtual function to enemy interface, it became an abstract class 05:23.630 --> 05:30.650 and you cannot instantiate an abstract class without overriding its pure virtual functions. 05:30.920 --> 05:33.290 So we have to override both of these. 05:33.320 --> 05:39.620 I'll go ahead and copy both of them and come back to Ora Enemy and create a public section. 05:40.610 --> 05:42.210 I'm going to paste them in. 05:42.230 --> 05:45.580 Now, we're not going to put equals zero here. 05:45.590 --> 05:53.000 What we do is we mark these with override instead to make it clear that we're overriding these and we 05:53.000 --> 05:55.640 can create some function definitions for them. 05:57.560 --> 06:00.650 So generate definitions by declarations. 06:00.680 --> 06:01.970 Click okay. 06:01.970 --> 06:05.720 And here we have highlight actor and Unhighlight actor. 06:06.350 --> 06:12.170 So now that our enemies implement this interface and we have the ability to call interface functions 06:12.170 --> 06:18.320 on any actors that we know implement this interface, we can now set up our player controller to see 06:18.320 --> 06:25.010 what actors exist under the mouse cursor and if they implement that interface, we can highlight them. 06:25.010 --> 06:26.690 So that'll be the next thing we do. 06:26.720 --> 06:31.640 For now, we can compile this and make sure we have no compiler errors. 06:31.640 --> 06:36.900 And with a successful build, we'll wrap up this video and continue in the next one. 06:36.920 --> 06:38.090 I'll see you soon.