WEBVTT 00:06.920 --> 00:08.120 Welcome back. 00:08.270 --> 00:14.990 Now we're changing our attributes and we've seen that our health can go into the negatives and we can 00:14.990 --> 00:19.670 also fill up our health bar and continue increasing health. 00:19.700 --> 00:21.070 Same goes for Mana. 00:21.080 --> 00:24.600 In other words, we're not really enforcing any clamping. 00:24.650 --> 00:29.800 Now, there are different ways to enforce clamping, and in this video we're going to learn one of them. 00:29.810 --> 00:33.130 We're going to go into our attributes set. 00:33.140 --> 00:39.590 So I'm going to open my public folder, go to ability system and open Aura attribute set. 00:39.800 --> 00:46.400 And here in the public section, I'm going to override one of the functions that we've inherited from 00:46.400 --> 00:48.260 the attribute set class. 00:48.260 --> 00:51.290 So it'll be virtual and it's a void function. 00:51.290 --> 00:56.960 And the function I'm interested in is called pre attribute change. 00:57.350 --> 01:03.740 Now writer is offering to fill out the rest of it for me, so I'm going to go ahead and let it do that. 01:03.740 --> 01:10.230 And as you can see, it takes in a const reference of a gameplay attribute, the gameplay attribute 01:10.230 --> 01:17.550 struct and a float called new value and notice the float is passed in by reference and it's not a const 01:17.580 --> 01:24.630 reference that should hint to you that we can change new value and something somewhere is going to change. 01:24.630 --> 01:33.210 Now let's go ahead and generate this definition and let it call the super version of pre attribute change. 01:33.210 --> 01:40.920 And I'd like to just see what happens in this function when we change an attribute. 01:40.950 --> 01:46.590 Now, here's the cool thing about having an gameplay attribute here. 01:46.590 --> 01:54.750 In the input parameter list, we can check that attribute and see if it's equal to any of our attributes. 01:54.840 --> 02:01.830 We can use comparison operators to compare gameplay attributes. 02:01.830 --> 02:05.070 They override the double equals operator. 02:05.070 --> 02:14.400 So for example, we could say if attribute double equals and we can get any of our attributes thanks 02:14.400 --> 02:21.210 to the attribute accessors, we can say get health attribute, for example, and we can compare and 02:21.210 --> 02:25.740 see if the attribute is our health attribute. 02:25.860 --> 02:32.490 Now, when any of our attributes change, whether it's from a gameplay effect or from being set directly, 02:32.520 --> 02:40.620 this function will kick off in response and it's called pre attribute change, which means it's kicked 02:40.620 --> 02:43.650 off before the change actually occurs. 02:43.770 --> 02:50.790 Now this gives us the opportunity to do something preemptively, but we really shouldn't be firing off 02:50.790 --> 02:53.820 events or kicking off gameplay logic here. 02:53.820 --> 02:58.680 Epic recommends that we only use this function to do clamping. 02:58.680 --> 03:06.540 Basically, that's really all it's good for now, just for demonstration and educational purposes. 03:06.540 --> 03:11.930 We're going to place a log here, so we're going to say you log, we're going to make it a log temp 03:11.940 --> 03:12.930 with warning 03:15.480 --> 03:23.580 and we're going to say health percent F and we'll pass in new value. 03:24.390 --> 03:28.410 And I'd like to do this for all of the four attributes we have. 03:29.250 --> 03:38.040 So I'm copying it and changing this to get max health attribute and changing the comment to say Max 03:38.040 --> 03:41.220 health and I'll copy both of these. 03:41.340 --> 03:44.460 And instead of health we're going to change it to Mana. 03:44.490 --> 03:51.630 I'm just going to highlight this section and here in writer I can hit control H, I can search for health 03:51.630 --> 04:00.690 and I can replace with mana and I see that I have get health attributes, health get max health attribute 04:00.690 --> 04:01.530 max health. 04:01.530 --> 04:03.210 I'm going to replace all. 04:03.210 --> 04:07.320 And now these are the mana versions. 04:07.560 --> 04:09.020 Okay, cool. 04:09.020 --> 04:16.370 And in Visual Studio it's control shift f I believe to find and replace. 04:16.370 --> 04:22.580 Just make sure you know what you're doing there and I'm going to go ahead and close that mini menu. 04:22.580 --> 04:26.600 And now we're seeing when any of our attributes change. 04:26.600 --> 04:33.260 Now let's go ahead and run this in debug mode and change some attributes and see what we get printed 04:33.260 --> 04:34.700 to the output log. 04:35.640 --> 04:40.860 Okay, I'm back in the editor and I'm ready to test out some changes. 04:40.890 --> 04:47.850 Now let's make sure we understand what each of our aura effect actors are doing right. 04:47.850 --> 04:50.670 We have health potion and mana potion. 04:51.150 --> 05:00.690 And we know that those use these GE potion heal and mana and these are instant gameplay effects which 05:00.690 --> 05:07.020 means we know that they permanently change the base value of those attributes. 05:07.140 --> 05:11.340 Now we also have these crystals and these are different. 05:11.370 --> 05:15.840 They have duration and they also are periodic. 05:15.870 --> 05:22.830 Now, because they are periodic, they act like instant effects, so they also permanently change the 05:22.830 --> 05:23.940 base value. 05:24.570 --> 05:30.150 We also have area the GE Fire area is periodic as well. 05:30.150 --> 05:37.320 So all of these affect the base value permanently because they're either periodic or instant. 05:37.350 --> 05:39.150 Now let's open the output log. 05:39.150 --> 05:43.620 I'm going to dock it in the layout and bring it down here. 05:44.430 --> 05:51.390 So that I can see it and I'll go ahead and press play and let's see what happens if we pick up a mana 05:51.390 --> 05:52.110 potion. 05:52.140 --> 05:55.080 Here we see Warning Mana 40. 05:55.110 --> 06:00.350 Let's pick up the health potion and it says warning health 75. 06:00.360 --> 06:04.770 I'm going to show debug just so we can compare and make sure that these are correct. 06:04.770 --> 06:06.450 And sure enough they are. 06:06.480 --> 06:15.030 Let's go into the fire volume and we see that our health is going down, going down by looks like one 06:15.030 --> 06:16.980 per second as expected. 06:17.070 --> 06:21.030 And let's go ahead and pick up a mana crystal. 06:21.640 --> 06:23.020 And we see it going up. 06:23.020 --> 06:26.470 And let's pick up a health crystal and we see it going up. 06:26.860 --> 06:35.590 So as we can see, we have pre attribute change being called in response to these attribute changes. 06:35.860 --> 06:37.420 Now here's the thing. 06:37.420 --> 06:45.250 It's called pre attribute change, which means we have the opportunity to perform some sort of clamping 06:45.250 --> 06:47.980 before the change occurs. 06:48.220 --> 06:50.830 So if we change this new value. 06:50.860 --> 06:52.630 Well what happens? 06:52.810 --> 06:53.240 Right? 06:53.260 --> 06:55.210 Because we see that it's passed in by reference. 06:55.210 --> 07:00.640 So is that going to actually change the attribute value? 07:00.790 --> 07:02.500 Well, let's find out. 07:02.530 --> 07:08.580 Let's say we don't want our health to ever go above our max health, for instance. 07:08.590 --> 07:14.890 What we can do is we can set new value equal to the result of a clamp. 07:14.890 --> 07:21.800 So f math clamp, we're going to clamp new value. 07:22.610 --> 07:29.030 And we'll clamp it between zero and let's say, our max health. 07:29.030 --> 07:31.100 So get max health. 07:32.400 --> 07:38.460 And now, as our health value changes, it'll never go below zero or above max health. 07:38.550 --> 07:41.100 Let's do the same thing for mana. 07:41.130 --> 07:49.260 So down here, if attribute is the mana attribute, we're going to say new value equals new value but 07:49.260 --> 07:54.790 clamped between zero and instead of max health we'll say max mana like so. 07:54.810 --> 07:58.350 Now let's go ahead and run in debug mode. 07:59.320 --> 08:00.130 All right. 08:00.130 --> 08:03.040 And we're going to go ahead and press play. 08:03.040 --> 08:09.580 I'm going to show debug ability system and let's start picking things up. 08:09.580 --> 08:12.190 Let's go to the nanocrystals first. 08:12.220 --> 08:14.680 We have ten mana max Mana is 50. 08:14.680 --> 08:16.390 I'm going to pick up a health crystal. 08:16.420 --> 08:20.620 We go up to 20 picking another one up we go up to 30. 08:20.650 --> 08:25.150 Another one we go to 40 and another one we go up to 50. 08:25.150 --> 08:28.690 And I think we have a man of potion over here if I pick that up. 08:29.460 --> 08:30.480 Look at that. 08:30.510 --> 08:32.670 We actually stay at 50. 08:32.700 --> 08:35.190 Now that mana potion does work. 08:35.190 --> 08:38.400 Right, Let's pick up the mana potion first. 08:38.430 --> 08:38.940 There. 08:38.970 --> 08:39.240 See? 08:39.240 --> 08:40.650 We see that it does work. 08:40.650 --> 08:44.850 We have 40 mana, but if we pick up a crystal, we go up to 50. 08:44.850 --> 08:48.090 But if we pick up a second crystal, look at that. 08:48.090 --> 08:48.960 Nothing happens. 08:48.960 --> 08:49.260 Why? 08:49.290 --> 08:56.700 Because before the attribute changes, we have the opportunity to do something in pre attribute change. 08:56.700 --> 09:02.700 And because we're clamping it and we can't go above max mana, which is 50, we're preventing that mana 09:02.700 --> 09:04.770 from going above the max. 09:04.800 --> 09:06.180 We're clamping now. 09:06.180 --> 09:10.110 The same goes for the health and it goes both ways, right? 09:10.110 --> 09:13.980 We clamped so that the health cannot go below zero. 09:14.130 --> 09:20.700 But this takes one away every second, which means I'm going to have to wait for Looks like 40 more 09:20.700 --> 09:22.590 seconds to test that out. 09:22.590 --> 09:23.850 That's going to take too long. 09:23.850 --> 09:25.770 So I'm just going to test the other way. 09:25.770 --> 09:27.690 I'm going to pick up a health potion. 09:27.690 --> 09:30.460 I'm going to pick up the health crystal. 09:30.700 --> 09:32.490 Is it enough to push me over? 09:32.500 --> 09:34.030 No, but that's fine. 09:34.030 --> 09:35.590 I believe that it's working. 09:35.590 --> 09:39.610 We saw that it works for mana, so that's pre attribute change. 09:39.760 --> 09:47.530 And again, it's not really meant to kick off any logic, it's really just meant to clamp and that's 09:47.530 --> 09:48.640 what we're going to use it for. 09:48.640 --> 09:53.950 So before the attribute changes, we can perform clamps. 09:53.950 --> 10:02.440 I don't really feel like I need all of these logs and I'm not really going to clamp our max mana and 10:02.440 --> 10:03.160 health. 10:03.160 --> 10:07.920 I mean, I guess we could clamp it so it doesn't go below zero. 10:07.930 --> 10:11.170 But for now I think I'm fine without clamping those. 10:11.170 --> 10:16.420 I'm going to go ahead and remove all of these logs. 10:16.420 --> 10:22.570 I don't feel like we need them, but I'm going to leave our clamping for health and mana. 10:22.570 --> 10:25.660 I think those are useful, so we'll go ahead and leave those. 10:26.490 --> 10:34.490 So pre attribute change is where we can modify the changes to the current value of an attribute. 10:34.500 --> 10:39.000 And this function is called before the change actually happens. 10:39.030 --> 10:44.040 Now that is a significant detail and we'll see why in a second. 10:44.370 --> 10:50.520 Pre attribute change is triggered by changes to attributes, whether that's through attribute accessors 10:50.520 --> 10:56.940 like the setters that we've created thanks to our boilerplate macros or due to gameplay effects. 10:56.940 --> 11:00.900 Literally anything that changes the attribute can trigger this function. 11:01.140 --> 11:06.990 Now, this does not permanently change the modifier for a given attribute. 11:06.990 --> 11:12.510 It just changes the value returned from querying the modifier of the attribute. 11:12.510 --> 11:19.650 In other words, we can clamp changes before the change happens, but there are later operations that 11:19.650 --> 11:27.340 happen after pre attribute change and these will recalculate the current value from all modifiers involved. 11:27.340 --> 11:34.450 So if the value of health changes, for example for any reason, then there are later operations that 11:34.450 --> 11:41.590 will recalculate that health change, which means that our clamping will have no effect and we'll have 11:41.590 --> 11:43.810 to clamp again later on. 11:43.810 --> 11:51.190 So pre attribute change is not the most attractive choice to implement final clamping changes, but 11:51.190 --> 11:52.210 it is there. 11:52.480 --> 11:59.590 Now you may be curious as to what might be the best function to implement something for when an attribute 11:59.590 --> 12:02.470 changes and be sure that that change will be final. 12:02.470 --> 12:06.430 One of those functions is called post gameplay effect execute. 12:06.460 --> 12:12.910 This actually happens after a gameplay effect has changed an attribute and we're going to learn about 12:12.910 --> 12:15.310 this function in the next video. 12:15.340 --> 12:16.540 I'll see you soon.