An Introduction to Scripting in Stingray (3ds Max Interactive)

DAVID MENARD: First question to all of you here. Who has never, ever written a line of code in their life? How many of you? OK. That's about five. And this is perfect. I'm going to just put this a bit lower. The class is really designed for a basic introduction for anyone who's never, ever scripted in their life. For everyone else, I hope you're going to find something here. Don't hesitate to ask questions along the way. I purposefully shortened the material of the class, so that we have enough time to chat, to ask questions. And hopefully the pace, I'll try and keep it very constant.

So first things first. Before I even introduce myself, everyone just open 3dsMax Interactive or Stingray. You have Stingray? Click on Templates, and just double click on the Basic template. Create one, and we're going to let that compile while we do the rest. And I think everyone here is on trial. So you can just close that window, and it's going to compile.

All right. So my name's David Menard. I work for Autodesk. I'm Product Owner for Revit LIVE. I joined Autodesk three years ago as a programmer. I went to school in programming four years, got a Bachelor of Engineering. This means I kind of have an unfair advantage, as well, here. Because obviously, I've spent four years studying to program. And Lua is all about programming, which is why I invited Paul with me-- where's Paul?

PAUL KIND: I'm over here.

DAVID MENARD: All right, Paul. Come up here. And Paul is kind of my success story. He's an artist-- well, I'll let Paul introduce himself. He's my success story. Win!

PAUL KIND: Hello? Plug in? Remote?

DAVID MENARD: Yeah.

PAUL KIND: On. So I guess you guys might be wondering about Lua a little bit. And first I'm just going to start with who I am. So I'm an artist. I started with pretty much being an artist-- a 3D animator mostly, or 3D modeling. Basically game art. And that's where I started with.

And I started using Stingray quite a bit. And I was actually on the Stingray team doing all the content for Stingray. And after very short order, I started working with Flow. And Flow took me to a really good place. And then I started to realize that I needed to do more than just what Flow can do-- not that Flow can't do it. But there's some times when you just want to make everything a little easier for yourself.

And luckily, with Lua, you can do that very easily. And you can create your own Flow nodes. And I'm pretty sure that's what we're going to be learning here today is how to create your own Flow nodes. And once you learn that bit, you can start really accelerating what you do in Flow.

So yeah, so I started in with Flow. But as an artist, I had no programming background-- or very, very little. I think I used Lingo, which was in Director from years prior. So yeah, if I was able to pick it up as an artist, I'm pretty sure that anybody can. It's not super complicated. And I would just say, take it one step at a time, learn slowly, and you guys are going to do great. But yeah, it's super awesome.

So some of the things that I've done since then-- because now, it's like an addiction. Once you start making Flow nodes, you're like, oh, here, let's make more. So I have a whole library. It's available online, I think. Oh, we're not showing it. But if anybody is interested in downloading a library of already pre-built Flow nodes, just let me know, and I will give you the link to it. Or maybe David can put it up on screen.

DAVID MENARD: Yep. Keep talking.

PAUL KIND: OK. Yeah. So that's a repository on GitHub. You can download the whole package. And once you have the package, it gives you a whole bunch of new Flow nodes. And you can use that to figure out how to write your own Flow nodes. And I was actually super surprised, because I had never actually thought anyone was even touching them. And I've talked to so many people here at AU that have been like, oh, my god, I found your Flow nodes. They're amazing!

So yeah, and it's super easy. It's really something anybody can pick up. And I really hope you guys do great with this class. And I hope that Lua works out well for you.

DAVID MENARD: So by the way, the link is available in one of our downloads on the AU class. So let's talk a bit about how this is going to work. By the way, those who just joined us, just make sure you open Stingray, and you start a basic project, so that it compiles while we talk.

So how it's going to work. First of all, I'm not going to present any videos. You know that usually, when you have hands-on labs or anything else, you prepare videos so that nothing goes wrong. The reason there is no videos, and the reason we didn't rehearse that much this class, is that when you're programming, you're going to make mistakes. It's completely inevitable that you're going to make mistakes.

So today when I write the lab, or when I do it with you guys, I want to make mistakes. And if I'm not making mistakes, I'm going to make intentional mistakes, to show you how to find your mistakes, and how to debug those mistakes. And I've found that that's the hardest thing to be able to teach, when you're teaching programming, and when you're teaching new programmers. It's not writing the lines of codes. It's really finding your own mistakes, and finding what's wrong with it. So making mistakes is part of the lab.

Next, we're going to actually follow the handout pretty line by line. So the handout is very detailed. We're not going to get to the end of the handout. We're only going to get about halfway through. If we have enough time, we might answer some questions about the rest. But by the end of the class, you should be able to do pretty much what Paul described-- writing Flow nodes, writing your own code, writing your own Lua functions inside of that. And writing really your own behavior inside of a Stingray or Max Interactive.

So before we get going, I just want to introduce our lab assistants. Guys, just come up here. And they can introduce themselves.

IGOR: Hello, everyone. My name is Igor. I am CTO of IM Designs. And I'm a nerd, and I like real-time rendering technologies. That's what we do.

RAVI: My name is Ravi Ray Wood. I'm an Architect and BIM Manager with Charles Hilton Architects out of Greenwich, Connecticut. And we do luxury houses of like $100 million single houses. So thank you.

DAVID MENARD: So thank you. Excellent. So these two guys are like Paul. They're self-taught as well. They started Lua with Max Interactive. So if you have any problems during the lab-- if you're stuck somewhere, if you have questions that are a bit more personal, just raise your hand really high, and yell out one of their names. Or yell out Lua or something. And they'll come and see you.

And to our lab assistants-- if you see that there are too many questions at the same time, just tell me. Raise your hands, signal me, and I'll take a break. And maybe I'll go and try and help. All right? So we'll try and keep this as casual as we can. It's late in the AU, and we're all kind of tired. Hopefully everything goes well.

All right. So let's get started. The first thing I want to mention is, throughout this entire lab, we're going to be building to something that's available in the online assets. Inside Scripts here, there's one thing called the Stingray App Kit Extensions. If you get to the end of the handout, you're going to end up with this. So this is pretty much a great example of where we want to get to. But we're not going to get to it by the end of the class. We're just going to get about halfway through.

All right, let's get right into it. The first thing every single programming class gives you, or has you do, is the Hello World. So most of you are familiar with the Stingray project structure. There's this little folder called Scripts here. And in there, there's the Lua folder. There's a file called project.lua right here. If you double click on it, you're going to open this. And this is pretty much the entry point to every single project.

Some of you have probably tried changing the default project. This is the default level that you're going to load. This is where you do it. But really, the first thing you want to do is at line 29-- or OK, the lines changed. But right here. We're going to write, print hello world, like this. And this-- congratulations. You've written your first line of code. So I think we've had five people who never wrote first line of code. Well, there you have it.

So this is pretty simple. Obviously, now, whenever we click on Play, if we go in the log console-- and nothing works, of course. See? First mistake, and this was already unintentional. I put a little dash here. I'm just going to delete that. That's not compiling. So saving this again. And when you press on Play, basically when the project plays, you're going to see hello world in the console. Now it's just compiling again. So I'm going to wait just a second.

While we wait, I'm going to give you a little pro tip. If you go in the window up here, there's a window called the external console. I almost exclusively use that to program in Stingray. The reason is that it has a debugger that I feel is a bit better than the default one. So in here, if you click on Lua, and open debugger, you're going to get a window in which you can open any project file, by just clicking Open. I'm just going to Open Project without Lua here.

See this, Create Lua Project? Open this, and we're good to go. It's the same file. I can save from here. And we'll get into what the debugger does. By the way, did anyone else have this wonky character here? Or was it just me? It was just me? Everyone else compiled properly? I'm asking you.

[INTERPOSING VOICES]

OK. Very. Fair enough. And I saw [? Takahashi ?] just walked in. Where is [? Takahashi? ?] OK. We have another lab assistant, [? Takahashi, ?] right here. He's going to help us through the lab, as well. Thank you.

AUDIENCE: Does anyone have a connector for the external [INAUDIBLE]?

DAVID MENARD: Hm?

AUDIENCE: Connector for the standard [INAUDIBLE]?

DAVID MENARD: I didn't get that. All right, so this is almost compiling. By the way, every time you change something in the project, it has to recompile. The reason it didn't compile here for the first time when I loaded it is because I had a programming error. Obviously, it'll block the compiler at this point. So we just have to wait it out. Hopefully, everyone else is fine. And we can keep going.

So in Lua, when you write a script, every single command that you write is going to be executed in a very linear fashion, right? You write print hello world, you write print hello world number two right after that. They're going to get executed sequentially. And there's really no magic to it.

If something is happening in your experience-- in your game or anything that you write, basically, I am afraid to say it, but it's your fault. The computer won't do anything magical. It'll just follow your instructions by the book. And I mean very, very literally. And it'll surprise you sometimes how by the book it'll do things. I'm getting some echo now.

So if I write, for example, print hello world, a second thing here-- second thing-- it'll just print them in the order. And caps are important. You see I put a capital P here. That would generate an error. I'm just going to change it to a small p. All right. I've finished compiling, I can finally run my game. And in the log console, we're going to see the print hello world.

Oh. That's why. I was compiling for the Hololens. Of course.

AUDIENCE: Under the compiler, how did you get this [INAUDIBLE]?

DAVID MENARD: Simply click on Open, or Control-o. All right. So see? Hello World is being printed. Perfect. That's exactly what I wanted. All right.

So obviously, Hello World is really genius. It's fun. We've written our first line of Lua. Yea. But now we want to actually do something that's interesting with the engine. Like the way you interact with the engine is not going to be by printing stuff. You want to be able to call the application programming interface, or API. So the engine API is just a way to interact, to call things that the engine can do, such as spawning units, moving units, detecting collisions-- that kind of thing.

And your best friend when writing Lua scripts is the documentation. So under Help here, I want everyone to click on Documentation. Here. It's going to give you this page. And right here on the left, you have Lua API Reference. Your best friend is exactly this. You click there, and this page will detail everything you can do to interact with the engine.

For our purpose, we're going to start with spawning a unit. That is done under-- actually, I can search here. Spawn unit. And you're going to see that I have World dot Spawn Unit. And we're going to use exactly this function. When you call these-- these are called functions. It's just ways you can interact with the engine. And you'll get used to this. We're going to come back to functions, and how to write your own.

So the documentation says, I need to call Spawn Unit, and give a few arguments. These things are information arguments-- are information I need to give to the function, so that it knows what to do when spawning a new unit. Obviously, I need to give it a world, because this is under World here. Self is the world. I need to give it a unit name, so which unit to spawn. I need to give it a position, and then orientation.

So let's get back to Stingray, or Max Interactive. By the way, I'm just going to say Stingray from now on. It's shorter. That's the reason. OK? And I'm going to go in my script, and at the same place that I printed this, my hello world, I'm going to spawn a unit.

So the way you interact with the engine, or the API, the application programming interface, you always start with Stingray dot. So in our case, I was looking at the World API. So I'm going to go Stingray dot World dot Spawn Unit. So if I look at spawn unit, it says, Self. Self means just the world. So I'm going to give it a world. This-- we'll get back to what the app kit is, by the way. It's just app kit dot managed world, dot world.

Then I'm going to give it a unit name. The unit name in this case is simply the path. And the relative path of the unit in your project. So I'm going to try and spawn my cube. My cube is under Content. And let's look at this. Content, Models, Props, and [INAUDIBLE] box. I'm going to copy this, because I'm never going to remember what it is. And I'm going to give it exactly this-- content, slash, models, slash, props, slash-- paste whatever I copied. Then I'm going to go back to my API, just to look at what I need to give it. Position orientation.

And you see this little interrogation mark? The question mark here just says it's optional. So I don't actually need to give it a position or an orientation. If I don't, and if I read this properly, it's just going to spawn it at 0,0,0. Right? So I'm going to do that, and hope everything works well.

So this is my preview. I moved this box, just to make sure that it's not in the way. Because if I spawn a box inside the box, I'll just think nothing happened. So I'm gonna click on Start, and-- was that my new box? That is my new box, spawned at 0,0,0. And you see, this is my other box. So there we go. We spawned a first box. We interacted with our engine for the first time.

Now obviously, there is a Flow node that does this. This is not too interesting. But it is the first time we called an API, right? So let's say I don't want to spawn it at 0,0,0. If I go back to my documentation here, it says that the third argument I give it could be the position. Let's do that. Let's give it a position.

So I'm going to do Stingray, Stingray dot vector 3. And I'm going to give it a position. Let's say 10, 10, 0. Stingray, if you remember correctly, is z up, right? So the up vector is in the z direction, or zed direction, if you're Canadian, like me. It's important. It's an internal fight.

So next, when I plus on Play, the first thing that's going to be spawned is my cube, and at a different position. So yea, now I have full control over this. So anyone has a question up to now?

AUDIENCE: Can you put the script back up?

DAVID MENARD: Oh-- yeah. I'll put the script back up. There we go. I'm going to try and make this a bit bigger, too. And if your line is too long, you can simply index it. So you can write the same line on different lines. It won't do anything.

AUDIENCE: Is that the product of [INAUDIBLE]?

DAVID MENARD: Yes. So from I had the question earlier, how to open this file. When you're in the external console, you have to go into Lua open debugger. Once you're in the debugger, you simply click Open, and start writing stuff here to search for it. It's Script, Lua, Project. So I'm going to wait a second, just for everyone to make sure you catch up.

So let's go back to our documentation for a second. This here-- the Spawn Unit function-- you'll notice at the end, it says, column Stingray.unit. This means it returns something. So when you spawn the unit, it will return a reference to that unit, so that you can use it later on. And we're going to store that in something called a variable that we can use later on.

And a variable is really anything you can dream of. You call it what you want. You store whatever you want. And it's just something to help you store information and use it later on. So the way you declare a variable, you simply name it.

In our case, we're going to use the Local keyword. That just means that the variable is only available inside this function. I'm going to call it, let's say my box is actually a chair, because we like chairs. So now, the unit that I spawned-- the box-- I called it a chair, because I think I'm going to use it as a chair later on. I can use this to later reference it, and maybe change its position. And let's actually do that.

So how will I change its position? Well, now I have to go back to the documentation, because obviously, I don't know how to change a position of a unit. I think it's probably going to be inside Unit. So I'm going to open the Units documentation here, and probably going to search for something like set position. No. I'm going to search for position then. There you go-- local position or set local position. Perfect.

So I'm going to use this function on my unit to be able to set its position some other time. And there is an i integer here, the index of the node. So my box, I only have one node in it. I think I only have one node in it. So let's try 1. So here, I'm going to do same thing-- Stingray.units.set_local_position. I'm going to give it my chair. Right? That's our first argument. If you look at the documentation, Self is always the kind of upstream API. So this chair.

The index-- I said I'm going to try 1, because a node is always 1, in my case. And I'm going to give it a new position-- Stingray.Vector3. So do I have to explain what a Vector3 is? Or is everyone good? Does anyone not know what a Vector3 is? OK. Vector3. Perfect.

A Vector3 is basically just three numbers in a row that you can use. Usually, they're used for positions. You can use them for rotations, as well. So in a game engine or a 3D world, you have three axes. Right? x, y, z. Well, Vector3s will describe positions on those three axes. Excellent.

So a Vector3. I'm going to give it a new position-- let's say 20,20,20. So my cube is going to end up in the air. So now, if I press on Play-- where is my cube? It's up here. There you go. So that worked.

All right. So we've seen with the API-- the application programming interface-- of the engine that we've been calling these things called functions. Right? Spawn Unit is a function. Set Local Position was a function. Now, let's build our own function. Functions essentially are just a set number of instructions that will get executed one after the other. And once you regroup those instructions together, you can reuse them as many times as you want.

So let's say you want to set the position of a unit-- its position, its rotation, and its color. You can put that in a function, give it three arguments-- position, rotation, color. And then, just call that on a single unit many, many times. So it's really useful for organizing your code. And you'll see that they are crucial later on to creating your own Flow nodes.

So let's just practice here and create a normal function that will do precisely exactly what we did. So in the same file, we're still in project.lua here. I'm going to call this function-- this is how you declare a function. Who knew? Function Spawn_A_Chair. You don't have to put underscores here, by the way. This is just kind of a programming style. A lot of people will do something like this. So I'll just do this.

Then the function here, you can give it as many arguments as you want. So I'm going to give it the unit to spawn, and I guess a position. This seems fair. And to end the function-- to tell Stingray where the function ends, you just type end. So now, inside of this-- inside Spawn_A_Chair-- there's a set number of instructions that I can reuse. Right now there is nothing, but I can still call my function. So I can do something like this.

Spawn a chair. Give it two arguments. So the first one, I said unit to spawn. I'm going to say this one. I'm just going to copy paste this, because I don't want to type all of this. And I'm going to give it a position, as well. Stingray.Vector3 just at 0,0,0. OK?

So this is how you call a function. You just open and close the parentheses. Is this OK, by the way? Who's following me? OK. About half the class is following me. So we'll take a tiny one-minute break, just to make sure that people can catch on.

Who has abandoned? Anyone abandon? OK. Do you want to try to catch up? Or are you just trying to follow?

AUDIENCE: [INAUDIBLE]

DAVID MENARD: OK. Because this happens a lot. Especially if you make a mistake at the beginning, it's hard to catch up.

AUDIENCE: Yeah, you just want to wait [INAUDIBLE] You're way too fast.

DAVID MENARD: Oh, OK. I'll slow down then.

AUDIENCE: Quick side question.

DAVID MENARD: Yeah.

AUDIENCE: Is Lua the only scripting language that Stingray uses?

DAVID MENARD: Yeah. So the question is, is Lua the only scripting language that Stingray uses? The answer is yes.

AUDIENCE: [INAUDIBLE]

DAVID MENARD: No. There is a C API, so C, C++ API, if you want to go that way. There are bindings between C and Lua, so you could implement your own scripting language. I don't think this is a subject we want to go into. [CHUCKLES]

AUDIENCE: But we can use C, C++.

DAVID MENARD: Yes. OK, so should I go back a bit? I just want to get some feedback.

AUDIENCE: Yes.

DAVID MENARD: Yes? On going back?

AUDIENCE: Yes.

DAVID MENARD: Back to where?

AUDIENCE: [INAUDIBLE]

DAVID MENARD: OK.

AUDIENCE: What [INAUDIBLE]?

DAVID MENARD: To spawning a chair, I guess. So if I go back here-- so remember, right. So if I explain variables again. So when you use the function-- the spawn_unit function-- I went to the API. There you go. And I'm just going to spawn, unit. So I obviously looked at the API and made sure that everything was here properly I think I should leave my code up a bit more, right? Does that make sense? OK.

AUDIENCE: David?

DAVID MENARD: Yep?

AUDIENCE: [INAUDIBLE] many [INAUDIBLE] algorithm for the [INAUDIBLE] people who have bad eyesight. [INAUDIBLE]

DAVID MENARD: There we go. So I'm going to delete my function. And let's make sure that everyone's following here.

[INTERPOSING VOICES]

AUDIENCE: Why would we be getting a nil value for this Flow?

DAVID MENARD: Hm?

AUDIENCE: You're getting nil value in manage world.

DAVID MENARD: Manage world dot world?

AUDIENCE: Yep. Manage world dot world. [INAUDIBLE] Thank you.

DAVID MENARD: Yep. This?

AUDIENCE: Yep. We're getting nil value.

DAVID MENARD: OK. The question is that we're getting a nil value here. So this is causing an error. It's probably-- are you in the right project file? I'm just going to go back, and go and help.

You're outside the project. You're outside the function. Put this in here. OK.

So we had an error over there. I think it's a good example. The error was that we wrote the Hello World and all our functions up here. So if you're not in this function, the project dot on level pre_flow, these are not going to be available to you. So make sure you just write it under this line here.

All right. So Dave Tyner's here as well to help. So don't hesitate to say hi to Dave Tyner. You saw him on the main screen yesterday. Now he's going to get red. [CHUCKLES]

All right. Let's keep going. Let's rewrite our function. Right? How we write a function? We just simply write function over here, and call it spawn_a_chair. And then write end two lines later, just to make sure that Stingray knows where we're ending. And what I'm going to do, at this point, I'm going to just cut these two lines that I had under on project load pre_flow, and I'm going to pass them up here.

And then, what I need to do to call this function-- I just need to open and close a parentheses. I'm just going to copy paste this, because it's safer. That's spawn-- yeah. And so this will actually call this function. So if I press on Play at this point, it's going do the exact same thing as it did before. It's going to spawn my unit. Actually, it's going to print "Hello World" first-- right here. It's going to print this second thing. Then it's going to spawn a chair.

And by spawning a chair, it's just going to go up in here, to line 30, and execute these two lines of code. So it's going to spawn the unit and set its position. I'm going to show you what that does. There you go. So the unit is spawned, and it sets its position. I'm going to come back to the code, give you a chance.

Is this pace a bit better, by the way, those who were still following? OK. Thanks.

AUDIENCE: So question here?

DAVID MENARD: Mm-hmm.

AUDIENCE: Now you're writing the function above the function?

DAVID MENARD: Yep. Yeah. We can talk a bit more about that later. There's something called scope that might be important. But it's not important here. Just make sure that if you-- yeah. You can write it above, and it's available down there.

OK, so I think this is a good opportunity to show you the debugger. Remember I said that we're going to make mistakes? Unfortunately, I didn't make too many mistakes, except just at the start. Let's say instead of spawn the chair here, I would have made a typo. Called him spawn_a_shair.

Now when I click on Play, I'm going to get some errors. You're going to see in the log console, it's going to say, "attempt to call global"-- can I? Hm. It's going to say up here, "attempt to call global spawn_a_shair a nil value." Usually when you see a nil value-- nil in programming, or in Lua, means nothing. It doesn't mean zero. It means nothing.

So this basically says, I tried to call spawn_a_shair. But it's nothing. It means it doesn't exist. Obviously, because I called my function spawn_a_chair. So this is a mistake. So I'm just going to go ahead and look. If you actually look here, it's going to tell you at what line you made the mistake.

So the debugger is friendly sometimes. In this case, it's very friendly. It's going to say line 42, I made a mistake. So right here, spawn_a_shair, I made a mistake. It didn't tell me exactly how to fix it. So I have to figure that out. But if I inspect the code a bit, I can see that I made a typo. So spawn_a_shair.

Next, I want to know what's happening in my code. Let's say it doesn't behave the way I want. Let's say here it spawns at 10, 10, 20, and I don't know why. These little dots that I put on the side here-- they're called breakpoints. For this to work, make sure that you have the proper tab open here-- the one that's printing most of the text. So this one-- before opening the debugger.

AUDIENCE: Question. If [INAUDIBLE] debugger?

DAVID MENARD: In the external console, you mean?

AUDIENCE: Right.

DAVID MENARD: Yes. It's only in there that you can put breakpoints.

AUDIENCE: OK.

DAVID MENARD: You can put some as well in the script editor. So if I open Lua here, and double click on this, you can put breakpoints on somewhere here. Or maybe they removed that. But to be honest, the external debugger is a lot better. So I would just recommend you use that.

AUDIENCE: Yeah, how do you get [INAUDIBLE]?

DAVID MENARD: To this?

AUDIENCE: Yeah. Just [INAUDIBLE].

DAVID MENARD: OK. Under Window, there is a external console. This is it.

AUDIENCE: How do you open the player [INAUDIBLE]

DAVID MENARD: So what was the question?

AUDIENCE: In that console, I don't see anything that says, open.

DAVID MENARD: OK. In this? It's under Lua-- Lua Debugger.

AUDIENCE: Thank you.

DAVID MENARD: And you'll see this is a console. It's basically writing the same stuff that you have in here. And the debugger lets you inspect your code. All right.

So once I have this, if I put a breakpoint, you're going to see that, whenever I hit Play in my game-- now it's all black. The reason it's all black is because my breakpoint was hit, and no code is being executed at all. OK? So it just stopped right here. And it didn't even execute this line of code. You can see in the console, there's no Hello World. In my external console, there's still no Hello World. So nothing has been executed.

And from here, you can step line by line to see exactly what the code does. So if I press Step Forward or Step Over-- the shortcut is also F10-- you can simply see, line by line, exactly what the code does. Hello World. Then when I press F10 once again, or step over, it just went, Second Thing. Then when I get to a function, I can either step over-- which will go to the next line of code right here-- or I can step into. And that's going to go inside the function.

Step into. Then you're going to see, I get to the line where I spawn my unit. And even if I press F10 here, now that this line has been executed, there's a chair in my variable called chair. You can even see it down here. There's a unit in it. But you still can't see anything.

The reason you can't see anything is because this is an interactive engine. It needs to update 30 times a second, or 90 times a second if you're in VR, or enough times a second so that it's interactive. If I paused it here, the world has a unit in it, but it hasn't been drawn yet, not even once. So for me to draw it once, I actually have to let it go.

So from here, I debugged what I needed. So I can press F5. F5 will simply tell the debugger, keep going until you hit a next breakpoint. And I don't have another breakpoint. So at this point, everything's fine. And I can stay interactive again.

AUDIENCE: Sorry. Do you have a breakpoint [INAUDIBLE] it's not stopping.

DAVID MENARD: OK, when it's not stopping, it's probably because a debugger was not opened with the right console window. Let me show you. Then I'll show you on screen after. So close this.

Has anyone been able to hit a breakpoint, by the way? I'm thinking there might be something with the VMs. Yeah?

AUDIENCE: I had to re-run it twice. [INAUDIBLE] that it finally went through.

DAVID MENARD: OK. That's kind of weird.

AUDIENCE: [INAUDIBLE]

DAVID MENARD: [INAUDIBLE]. So usually, with these, you just want to make sure you have the tab that's printing text whenever you press on Play. So let's say I press on Play. You see, there's text that's been printed here. I want to make sure I select this tab before launching my Lua debugger. And there's a good reason for this.

The reason for this is that I can debug more than one engine at the same time. I can actually debug a Hololens, if I have one connected, an Android device, iOS device. I can even debug the code that's running in the viewport here if I want to. But you need to have the right tab selected. If it's not working properly for you, try running the game instead of playing the level. The game will actually spawn another tab, and then you can hit the debugger, and it should still hit the same breakpoint. Let me know if that works. Cool. So that worked.

I'm going to repeat this. If you're having trouble attaching the debugger or hitting your breakpoints, just click on Run Game instead of Test Level. Run Game is going to start a new tab up here. You can see that's the one that is going to print text whenever I launch the game. And from there, I can open my debugger. And then my breakpoints will be hit.

All right. Are we good to keep going? Anyone want me to repeat something? Questions?

AUDIENCE: Can you scroll up a bit?

DAVID MENARD: Yep.

All right. Next we're going to jump. We have functions pretty down right now. We know how to call the engine API. Next, we're going to create our first Flow node. These are super useful, because they can encompass sets of functions that either don't exist in the current Flow graph, or a set of functionality or behaviors that you want to encompass or keep organized in your project.

A great example, as Paul mentioned earlier, he made a little laser teleport-- that's one Flow node. He wrote the code for that in about 20 lines, put that in a node, and now he can use it in the Flow graph as he wants. So writing Flow nodes is very similar to the same thing. We're going to have to create a function. But first, we're going to have to define our Flow node-- what it's going to look like, how it's going to appear in the Flow graph.

So once again, I'm going to go into my documentation. If I go back to the Help Home, and I search for custom flow-- let's search for custom flow. There's going to be a page somewhere here-- Create custom Flow nodes in Lua. This page describes really well the procedure to create custom Flow nodes. It will also describe some more advanced concepts for creating Flow nodes. I usually always have this page open when I create my own Flow nodes, because I just keep forgetting the concepts.

But for now, we're going to keep it simple. And we're going to open a file in the Scripts folder. In the Scripts folder here, there's a file called Global. And if I open this folder in Explorer, this is actually a dot script flow nodes. So guess what? All your Flow nodes will be described in here.

You can open it in the editor of your choice or the Stingray editor. I'm going to open it in the Stingray editor. Hopefully I can zoom in here. I can't. So I'm going to open it in another editor, and hopefully I can zoom in here.

So when you open a template project, there's usually at least one template node. Under nodes, you can see the bracket opens here and closes here. There's another bracket that opens here, closes here. So everything inside of this here is one node. So if I go in my Level Flow, and I look at this Example Print node, the category is "Project," and the name is "Example Print."

So if I go in Project in here, there is an Example Print node. And this is actually a custom node for this specific project. So we're going to do something very similar to this node right here. So first thing I'm going to do is, I'm going to copy paste this, because learning by example is always great. And I'm just going to copy paste the exact same thing right under it. So [CLICK] right there.

I'm going to call this "Open URL In Browser." And guess what this Flow node, what we're going to make it do. It's just going to pop any URL you give it into a browser page. Something that doesn't exist in Flow today, something that the engine provides through its API. But we want to expose it to Flow, so that we can add custom events to it.

The args part of your Flow node is what the Flow node will take in. Remember earlier, we had functions, and the functions took different arguments? The spawn unit function, for example, took-- what was it? A world? A position and a rotation. This is the same thing. This Flow node here-- we will tell it that it needs to take a URL, and that is a string. A string is just a series of characters, if you're wondering.

So ironically, here, right here, "string" is a string. The Category is where the Flow node will appear when I right click here. So if the Category is Animation, it will appear under Animation. If it's under Project, it will appear under Project. You can see that mine just appeared here, "Open URL In Browser."

You can create your own category, too. So I'm going to call this "DavidNodes."

AUDIENCE: Hey, David?

DAVID MENARD: Yep?

AUDIENCE: Why did you capitalize URL instead of [INAUDIBLE]?

DAVID MENARD: There is no good reason for that.

AUDIENCE: All right. But it matters?

DAVID MENARD: Yes, it matters. Capitalization matters. So the question was, why did I capitalize URL? I had no good reason to do that. It's just a personal choice. It does matter, though. If I capitalize it there, when I use it later on, it has to be capitalized. So capitalization matters.

AUDIENCE: So you left it in lower case when you type it in, because you have to take lower case.

DAVID MENARD: When you use it in a function, in the code, later on? Yes. Not when you type in the URL, though. That doesn't matter. Yes. Exactly. And I'll show it to you later. Here. I'll actually do this. So that it's stupid, and looks bad, and is prone to errors. This will make you go nuts.

OK. The last thing is the function here. And this is the most important one. Whenever you call this Flow node, this is the code that's going to be executed for this Flow node. Now here, it says, "ProjectFlowCallbacks.example." We're going to change this to "ProjectFlowCallbacks.open_url_in_browser."

And I'm going to stop there for now and go to my Level Flow. Is everyone good with this? So if I go to my Level Flow, what I want to do is, I want to call this whenever I press Space bar. So I'm going to first create a Flow node for keyboard button.

To search your Flow nodes like this, by the way-- my favorite function ever-- you just press on Tab. Press on Tab, then you can write pretty much anything, and it's going to find it. So if I want to spawn unit on position, I can look for stuff.

AUDIENCE: Does that work in the Unit Flow now?

DAVID MENARD: No, not yet.

AUDIENCE: No?

DAVID MENARD: No. I know. I'm so sorry. [CHUCKLES] All right, so the button name here, I'm going to just search for space. Going to Save. And now I'm going to write my custom node. I put it under David's Nodes, right? Yes. "Open URL In Browser." So whenever I press Spacebar, I want to open this URL. I'm going to say, www.Google.com.

And I'm going to press Play with this. Leave it there for a second.

AUDIENCE: Would this be a reason why a node wouldn't show up?

AUDIENCE: Yeah. Not getting an error.

[INTERPOSING VOICES]

AUDIENCE: I've got the casual read shows that open URLs, there's an option to add. And then, when I click that, there's nothing.

DAVID MENARD: No reason for that.

AUDIENCE: There it's copied and pasted.

DAVID MENARD: We're getting [INAUDIBLE]

OK, a lot of people are having problems with the Flow node not appearing when you click on it.

AUDIENCE: [INAUDIBLE] keyboard [INAUDIBLE].

DAVID MENARD: I'm going to answer that question in just a second. A lot of people are getting problems that, when you click on the node here, it just doesn't appear. It doesn't show up. I think it's a problem with the VMs. For some reason, the connection is not happening. Just restart the editor, and it seems to work after that. Are you getting the same thing, Dave?

AUDIENCE: Yeah, we restarted it.

DAVID MENARD: OK. And it seems to work fine.

AUDIENCE: Show it works on the [INAUDIBLE].

DAVID MENARD: The next question was, how do you get the Keyboard Button node? You can either search for it, under Input-- somewhere in here-- Keyboard Button. Or my preferred method is you press on Tab, and then you can search for nodes. So I simply search for keyboard, and Keyboard Button shows up. And from here you can select your button. We have another question over here? Or same thing?

Excellent error. Perfect.

AUDIENCE: Got a good one, then.

DAVID MENARD: We had an error that said, "Script Flow node definition not found." Is because the name in the definition of the Flow node was not found. It was capitalized. I'll show it to you. Just quickly, in the definition of the Flow node, we had someone go like this. And I don't want to point fingers, because I've done it many, many times.