1 00:00:04,490 --> 00:00:05,690 ‫Hello and welcome. 2 00:00:05,690 --> 00:00:11,630 ‫In this lecture, we're going to be learning about functions that live not in the level blueprint, 3 00:00:11,630 --> 00:00:14,300 ‫but on a particular blueprint class. 4 00:00:14,300 --> 00:00:20,120 ‫These are called member functions and are absolutely crucial to object oriented programming. 5 00:00:20,120 --> 00:00:22,700 ‫Let's dive in and see how they work. 6 00:00:23,150 --> 00:00:31,430 ‫So in our spawn projectile function, in the level blueprint, we have got a load of nodes here relating 7 00:00:31,430 --> 00:00:36,830 ‫to adding the impulse, getting the direction of the impulse, and getting the static mesh component. 8 00:00:36,920 --> 00:00:43,610 ‫All of these nodes use the BP projectile instance in depth. 9 00:00:43,610 --> 00:00:50,690 ‫Wouldn't it be great if we could take all of this code and move it in to the BP projectile so that the 10 00:00:50,690 --> 00:00:55,130 ‫code that deals with that data lives with the data itself? 11 00:00:55,280 --> 00:00:59,300 ‫Well, that's the entire point of object oriented programming. 12 00:00:59,300 --> 00:01:07,040 ‫So we can define object oriented programming as functions living with the data that they manipulate. 13 00:01:07,400 --> 00:01:09,080 ‫So how does this work? 14 00:01:09,080 --> 00:01:13,520 ‫How can we make functions on particular instances of things? 15 00:01:13,940 --> 00:01:20,420 ‫Well, one way we can do this will go to our be open up our BP projectile class and make sure we click 16 00:01:20,420 --> 00:01:27,020 ‫open full blueprint editor is you can see that in this full blueprint editor there is a my blueprint 17 00:01:27,020 --> 00:01:35,180 ‫pane and a function section so we can hit the plus arrow here to create a new function on the BP project 18 00:01:35,330 --> 00:01:35,810 ‫class. 19 00:01:35,810 --> 00:01:41,960 ‫And I'm going to name this function, print your name and this print your name. 20 00:01:41,960 --> 00:01:44,150 ‫Function should do just that. 21 00:01:44,570 --> 00:01:49,910 ‫You can see we've got a node that starts the execution of this function so we can pull off its execution 22 00:01:49,910 --> 00:01:52,460 ‫pin and type print string. 23 00:01:52,460 --> 00:01:53,810 ‫So that's going to print out. 24 00:01:53,810 --> 00:01:54,380 ‫Hello. 25 00:01:54,380 --> 00:01:57,200 ‫Not exactly the name of this function, is it? 26 00:01:57,200 --> 00:01:59,390 ‫But we'll sort that out in just a second. 27 00:01:59,690 --> 00:02:04,130 ‫So what we've got here is known as a member function. 28 00:02:04,130 --> 00:02:12,020 ‫A member function is a function on a class that always gets called on a particular instance of a class. 29 00:02:12,020 --> 00:02:18,320 ‫So you don't say, I'm going to call print your name on all BP projectiles. 30 00:02:18,320 --> 00:02:25,010 ‫You have to say, I want to call, print your name on BP projectile number one, or BP projectile that 31 00:02:25,010 --> 00:02:26,720 ‫has just been spawned. 32 00:02:26,720 --> 00:02:36,650 ‫So if we go to our level blueprint, what you would have to do is take the reference that came out of 33 00:02:36,650 --> 00:02:38,780 ‫spawn BP projectile. 34 00:02:39,020 --> 00:02:48,050 ‫And from that reference you could call print your name and you can see it automatically connects to 35 00:02:48,050 --> 00:02:51,920 ‫a special input node called Target. 36 00:02:51,920 --> 00:02:54,410 ‫And obviously you've got to hook up your execution pins as well. 37 00:02:54,410 --> 00:02:58,580 ‫I'm going to hook it up to happen after ad impulse. 38 00:02:58,580 --> 00:03:07,370 ‫But what's interesting about this special target input node is that if you go over to the BP projectile, 39 00:03:07,370 --> 00:03:08,750 ‫you'll see that print. 40 00:03:08,750 --> 00:03:12,830 ‫Your name has no such input node. 41 00:03:12,830 --> 00:03:14,750 ‫So what's going on here? 42 00:03:14,990 --> 00:03:24,230 ‫Well, implicitly, any member function has a parameter which is its current target or the current instance. 43 00:03:24,560 --> 00:03:32,030 ‫And you can get hold of this by right clicking in the blueprint event graph and typing self. 44 00:03:32,390 --> 00:03:37,910 ‫And you can see there is a node called get a reference to self and it just creates a self node like 45 00:03:37,910 --> 00:03:38,540 ‫this. 46 00:03:38,540 --> 00:03:45,980 ‫And then you can use this self object reference to get hold of any of the properties on this particular 47 00:03:45,980 --> 00:03:46,370 ‫object. 48 00:03:46,370 --> 00:03:53,270 ‫So if we wanted to get hold of the name of our BP projectile, you can pull off of the self reference 49 00:03:53,270 --> 00:03:57,110 ‫and type in get display name, which we've done before. 50 00:03:57,110 --> 00:04:01,250 ‫And then you can hook up the display name into our print string. 51 00:04:01,250 --> 00:04:09,890 ‫So now when we play and we fire off a new projectile, you can see it's printing the name of the projectile 52 00:04:10,310 --> 00:04:17,210 ‫and you can see for every new projectile I create, the name is a different one because the self that's 53 00:04:17,210 --> 00:04:23,750 ‫being referred to by the member function is a different self is a different projectile. 54 00:04:23,750 --> 00:04:32,390 ‫So we've learnt that self is a node available inside of member functions that always points to the specific 55 00:04:32,390 --> 00:04:35,270 ‫current instance that we are using. 56 00:04:35,270 --> 00:04:40,190 ‫So the whole point of looking at member functions in the first place, the reason we started was because 57 00:04:40,190 --> 00:04:45,680 ‫of these nodes in the level blueprint, the where we get the static mesh, we get the forward vector 58 00:04:45,680 --> 00:04:48,260 ‫and then we add an impulse to these. 59 00:04:48,560 --> 00:04:51,860 ‫These feel like they should live on the BP projectile. 60 00:04:51,860 --> 00:04:55,310 ‫And so that's what I would like to challenge you to do. 61 00:04:55,310 --> 00:04:58,730 ‫So this is a bit of an evolved challenge, but we're getting towards the end of the section. 62 00:04:58,730 --> 00:05:01,730 ‫So I will take you through step by step. 63 00:05:02,120 --> 00:05:03,950 ‫So we're going to make a launch function. 64 00:05:04,060 --> 00:05:05,800 ‫Shin on the BP projectile. 65 00:05:05,800 --> 00:05:07,810 ‫So create it on the BP projectile. 66 00:05:07,810 --> 00:05:08,890 ‫Go to that plus button. 67 00:05:08,890 --> 00:05:11,080 ‫Add a new one, name it, launch. 68 00:05:11,440 --> 00:05:18,700 ‫Then cut and paste the nodes over from the level blueprint into this newly created function of yours 69 00:05:18,700 --> 00:05:22,090 ‫and make sure you hook up execution pins and etc.. 70 00:05:22,510 --> 00:05:28,000 ‫Now you're going to try and compile this that we haven't done this very often in blueprints, but compiling 71 00:05:28,000 --> 00:05:34,390 ‫just allows you to essentially spell check your code and make sure that there aren't any errors that 72 00:05:34,390 --> 00:05:36,850 ‫the Blueprint compiler can foresee. 73 00:05:36,850 --> 00:05:43,660 ‫So the way you do this is you go to the button in the top left and you hit compile and if there are 74 00:05:43,660 --> 00:05:48,580 ‫any errors, they will show up at the bottom in the little pane called compiler results. 75 00:05:48,580 --> 00:05:53,530 ‫You can see I've got compile successful, but any errors will show up here and sometimes you'll get 76 00:05:53,530 --> 00:05:57,250 ‫a little bit of red on a node to indicate where the error is. 77 00:05:57,790 --> 00:06:03,730 ‫And I'd like to see if you can try and understand what that error is saying and try and fix the error 78 00:06:03,730 --> 00:06:07,480 ‫using the new self node that we have learnt about. 79 00:06:07,930 --> 00:06:15,850 ‫And then you need to go ahead and call that function from the level blueprint by dragging off of the 80 00:06:15,850 --> 00:06:18,130 ‫instance like we did for our print. 81 00:06:18,130 --> 00:06:24,760 ‫Your self node drag off of the instance of the new projectile created from the spawn node and call the 82 00:06:24,760 --> 00:06:25,960 ‫launch function. 83 00:06:26,200 --> 00:06:28,360 ‫Pause the video and have a go. 84 00:06:31,400 --> 00:06:32,000 ‫Okay. 85 00:06:32,000 --> 00:06:32,890 ‫Welcome back. 86 00:06:32,900 --> 00:06:39,320 ‫So I'm going to go over to our BP projectile, hit the plus button next to functions in the my blueprint 87 00:06:39,320 --> 00:06:47,090 ‫pane and type in launch to name the function that let's go back to our level blueprint, cut out the 88 00:06:47,090 --> 00:06:51,740 ‫nodes and go into the BP projectile and paste them in. 89 00:06:52,010 --> 00:06:58,550 ‫Now I've got to hook up the execution from launch to add impulse and now I'm going to hit, compile 90 00:06:58,550 --> 00:07:04,850 ‫and you see I get an error on the static mesh or get static mesh node. 91 00:07:05,060 --> 00:07:10,550 ‫And if you look in the compiler results, it says it uses an invalid target. 92 00:07:10,700 --> 00:07:15,290 ‫So target this input here is not correct. 93 00:07:15,290 --> 00:07:25,040 ‫Now as I recommended you do is you can right click and type in self to get a reference to self and then 94 00:07:25,520 --> 00:07:28,460 ‫bring that self into the target instead. 95 00:07:28,730 --> 00:07:34,490 ‫Now if you hit compile again you can see the error has gone away and it's compiled successfully because 96 00:07:34,490 --> 00:07:43,550 ‫what's going on is that it's now able to get the static mesh component from the current projectile that 97 00:07:43,550 --> 00:07:46,010 ‫this launch function is being called on. 98 00:07:46,490 --> 00:07:56,060 ‫So if we go back to our level blueprint now, we can take the output pin from our spawn actor and we 99 00:07:56,060 --> 00:07:59,930 ‫can type in launch to call our launch function. 100 00:07:59,930 --> 00:08:06,080 ‫You can see the execution pin was automatically hooked up for me and then out after the launch function 101 00:08:06,080 --> 00:08:12,500 ‫we can hook up our print your name function if we want to, although that was just for debugging and 102 00:08:12,500 --> 00:08:18,560 ‫demonstration purposes and if you test it out, you can see that it's still launching successfully. 103 00:08:18,590 --> 00:08:24,620 ‫Except now the code that deals with launching lives on the projectile itself. 104 00:08:24,620 --> 00:08:25,250 ‫Great stuff. 105 00:08:25,250 --> 00:08:30,980 ‫We've learnt about one of the core concepts of object oriented programming in this lecture member functions. 106 00:08:30,980 --> 00:08:32,780 ‫I will see you in the next one.