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Extending Games With Lua
RealDSmooth writes "2old2play.com has a nice article up about extending World of Warcraft, Neverwinter Nights, and other games using Lua, a light-weight programming language made specifically for enhancing and extending games. It goes into some great details about what's available today, and where Lua is heading in the future."
I think they need to take Bob's advice. Very irritating to read.
Lua was definitely not designed specifically for extending games. It is a general purpose scripting language designed to be easy to embed and easy to use. It has been embedded into a number of games because it is hightly suited for this kind of embedding, but it was not originally intended for games.
I've been working with Lua off and on for a while. I have to say that it is pretty darn cool. It is really easy to embed, really easy to extend, and really lightweight (about 90k or so). The language is very simple, but still supports a lot of advanced programming concepts like closures.
Time flies like an arrow. Fruit flies like a banana.
...for making game's cooler...
...past the shipping titles intentions...
...if you're games have Lua capabilities...
...and add-on's that you can download for free...
...and that's just the first two paragraphs...
...who's editing that site?
vk.
Dawn of War, an RTS game without resource harvesting as you know it, uses Lua too.
I suffer from attention surplus disorder.
It's like bastard child of a VB nun mistakenly locked in a room full of Perl madmen.
Turned me off from doing any scripting for WoW completely.
Neverwinter Nights does not use LUA, it uses our own scripting language, NWScript which has been developed from ground up in house and has nothing to do with LUA.
LUA was used for scripting in Baldur's Gate series however.
BioGeorg
Aside from the fact that it appears to have been written by somebody whose teachers apparently overlooked the usage of the apostrophe when teaching him English, the article didn't really say all that much. Reading the summary, I was expecting some details about Lua itself, or maybe even some information about where it is headed in the future. All the article pointed out was that Lua was being used in some games. ...... Real informative.
But seriously, Lua's a great language. Full lexical scoping and first-class functions alone give it insane flexibility and power, and its table data structure is implemented very well. In general, Lua is one of the most well-thought-out languages I've ever seen; its creators have taken great pains to get all of its functionality into it while still maintaining a low profile (the stand-alone interpreter takes ~150KB of space) without resorting to kludges or hacks, and these efforts have paid off. I wouldn't think of using anything else to extend a program.
Can some more knowledgable people post some pros/cons of using python for this, like issues with the byte-compiling?
"Lua, a light-weight programming language made specifically for enhancing and extending games"
:(
Wrong bitch!
Lua is *not* a language that was specifically made for enhancing games. True, it has a great use in enhancement and extension of games (in fact I use it in my game), but it is used in MANY pieces of software outside gaming. Here is proof.
For the bastards who are too lazy to click the link, here's a sample of the projects that use Lua (outside of gaming)
- Automatic configuration of network devices
- Heart Institute Monitoring Network
- CPC4400 Embedded Switching Platform
- Horus Alarm monitoring software
Unreal script is an example of a language designed specifically for games (or just a game in this case). Lua is not one of them. I would like to encourage the editors to check their submissions over thoroughly and stop mis-educating the Slashdot crowd. Of course, that's probably as likely to happen as Apple is to announce that they're switching back to PowerPC. We can hope, but it probably won't do no good.
Hero of Allacrost, a FOSS RPG for *NIX/*BSD/OS X/Win
My officemate literally just purchased Game Development with Lua. It is a neat book.
However, Lua is used for other things, includinge the ion window manager, the SciTE editor, the Elinks text webbrowser and more.
I embedded Lua into an as-yet-unreleased top-scrolling space shooting game (a la Raptor) and it is a very handy language for embedding. I believe it was originally designed as a language simply for configuration files, but is has grown into a capable (but very simple) language.
The entire manual that explain the whole language as well as the C embedding interface and the optional standard libraries is probably less than 100 pages printed. The source code is around 10,000 lines of C code, I believe.
Performance was also particularly impressive provided you know what you're doing. If you're new to functional programming, you might want to read up a bit. Also, it is a good idea to have experience with recursion and other such elementary topics.
Overall, I couldn't believe how easy it was to build Lua into my little project and I doubt I'll ever take a look at another scripting language because Lua is just that good.
The scheme I chose to use for my project is that it reads in all the Lua files in a directory and using the game engine's simple API (in Lua), different scripts add things like ships or new weapons. This allows the player to write a quick script for a new weapon (e.g. a rail gun), drop the script in a directory, start the game, and then use that weapon. There's basically no overhead. I think that's pretty cool and encourages people who don't know how to make an entire game to still have a fun time extending the game by themselves.
True story.
Link
I have to say that it really has helped the lives of mangband and tomenet. You don't need to be a fancy c programmer to add abilities to the games, plus you can make some of the changes live, which is really nice. Kind of neat, I just wish that some of the debugging tools were a little cleaner to work with.
Gonzo Granzeau
"Nothing the god of biomechanics wouldn't let you into heaven for.." -Roy Batty
As GoNINzo pointed out, it's nice to be able to make changes at runtime while creating a game. Being able to tweak behaviors without having to save_gamestate-> exit-> recompile-> restart-> reload_gamestate is a huge time-saver when you're fine-tuning. And anything that allows you to experiment easily will increase your ability to be creative. After all, many advancements come about accidentally through tinkering
Of course, it also coddles a bit of laziness on the design side, so if you're not careful, you end up designing ever-larger systems as you write them, rather than thinking them out beforehand. Not that I would ever fall into that trap. Repeatedly. Over and over again. Seriously, you'd think I'd learn.
www.dejobaan.com - Making games one game at a time.
We're indie. We're working on our 14th game.
... in order to create mini-mods of itself. And it's a mod. I think this is pretty dern cool
What's wrong with Neverwinter Script? It's a C-like language that was embedded since day one.
Has anyone touched the Game Monkey yet?
Seemed nice.
BytesTemplar.com
I spent a couple months scripting scenes for the Hero6 project. I don't know if the project is still active anymore, but the building of the game was heavily centered on LUA scripts that made event calls to the game engine, which I think was written in either C or C++. It was an excellent approach, and LUA was perfect for the job; it made development very simple and easy.
I read one of the links above, comparing Python and Lua, but it doesn't talk about sandboxes. Does Lua have one or does it just do multiple interpreters?
I have to say that Tcl is pretty good for this kind of thing too, although it is certainly bigger than Lua. It has sandboxes and multiple interpreters that you can control from both C and Tcl itself. You can also do threads, if you want. And the language is also pretty easy to learn for newcomers, like most scripting languages - especially considering the really friendly user community.
Of course, if you want really small, there are Tcl versions and related languages like Jim and Hecl .
http://www.welton.it/davidw/
I've embedded Lua into all sorts of things. Never really finished any of it, but I did embed Lua into the BUILD engine to replace the game code written in C. I've also been working on embedding it into Quake 3 Arena to do similarly, though unfortunately real life is getting in the way of doing much there. Lua is great because you can make what you want with it. It has no builtin functions, so it's completely up to the embedder what gets included. The bundled coroutine library is very useful in games, too. It doesn't even have an object model of its own, meaning that you are free to invent one based on the simple structures it provides.
The adventure game Grim Fandango was based on Lua, as was the latest Monkey Island game. Lua gets everywhere. It's in text editors, web servers, games, your shell... you name it. It's probably somewhere on your computer right now, hidden inside some application.
Well, the lua 'or' and 'and' shortcut logic operators are sort of cool because you get shorthands for using defaults for variables,
so instead of
PHP: doSomething(isset($a)?$a:-1);
you can do:
Lua-like: doSomething(a or -1)
This removes the redundancy in the php statement.
I felt the embedding of lua might be kind of hard, it looked like programming postscript to me
I read one of the links above, comparing Python and Lua, but it doesn't talk about sandboxes. Does Lua have one or does it just do multiple interpreters?
Both of those apply. As Lua is fully reentrant and tiny, you can have any number of Lua VMs active concurrently in a program, and they're all naturally disjoint from each other.
In addition, Lua execution is inherently sandboxed with respect to the operating system because the base interpreter provides no system functions at all, and so it can affect only its own internal state. You need Lua's standard libraries before you can do file operations etc with it, but those libraries are available only if the designer chose to link them in to your executable, so the sandboxing is unbreakable "by default", bugs excepted.
Diametrically opposed to the above, many other Lua executables exist which contain dynamic loaders to allow the interpreter to be extended on the fly with arbitrary code, ie. to provide high functionality rather than sandboxing.
Lua can be pretty much anything you want it to be. The base VM just gives you efficient and flexible scripting, and imposes no usage policy at all.
Re your point about Tcl, that language suffers from its string orientation when applied to gaming, although it's fine for embedding as a simple configuration language. Lua is stunningly fast, so its use in games goes far beyond mere configuration and UI scripting, right into the hearts of engines.
"The question of whether machines can think is no more interesting than [] whether submarines can swim" - Dijkstra
Sounds like the Lua approach is pretty smart for what it's meant for. Build it small and make it extensible is often a pretty good way of doing things. One thing that's missing from Tcl in terms of sandboxing that your comments don't exactly cover WRT Lua is the ability to really limit things. For instance, Tcl's sandbox won't stop a "while { 1 }" type of situation - you'd have to have a control thread or some other means of defeating it (it's certainly possible, just not as easy as it could be).
You do make a common mistake regarding Tcl though, that it is "string based and therefore slow". Tcl has been internally byte compiled for a number of years. I still don't think it's as fast as Lua, but there's more to it than just "string based", because while strings are very important to Tcl, internally it's bytecodes and the correct 'C' types.
http://www.welton.it/davidw/
Except, of course, for the fact that Neverwinter Nights doesn't use Lua at all. It's using a custom C-like language.
Lua's cool and all (and BioWare has used it for the Baldur's Gate games and the underrated MDK2), but it's not in NWN or NWN2.
In other game scripting news, Freedom Force and its sequal use the delicious Python.
- chrish
I don't know Lua, except for its name. But I do know UnrealScript very well (the scripting language of the UnrealEngine), a language that was written with games in mind.
Lua is just an interpreted programming language right? So you still need to create bindings from the game to the Lua environment. How difficult is that to do? How does Lua compare to using Python (for example) as script language? What makes Lua so great? Nothing about that in TFA, just some examples where it's used.
www.garry.tv
garry'smod, a half life 2 mod, currently is in the process of implementing lua into its framework, and with me being a gold member (read: Pay to beta), I get to see it, and there are some fsking sweet gametypes currently out for it...
-Hexagram
While I completely agree with your post, the last sentence bites me:
``I wouldn't think of using anything else to extend a program.''
I'd just like to propose Scheme as an alternative to consider. Scheme has all the characteristics you applaud: great design, immense flexibility, and low footprint. Comparing Scheme to Lua:
- Scheme is a Lisp dialect, and, as such, uses s-expressions (basically lists, think lots of parentheses). Some people find this annoying, but it makes the syntax very regular and easy to parse.
- Scheme has a reader that reads s-expressions and a writer that writes them. This is convenient for reading and writing data, but (since Scheme programs are built of s-expressions) also allows easy processing of program code.
- Scheme offers macros which can be used to extend the syntax of the language. Few other languages offer these; it seems to go together with the parentheses (things like C macros are nowhere near as great)
- Scheme is standardized, and there are many implementations; anything from simple interpreters to complete IDEs and high-performance compilers
- Scheme is old, and therefore less prone to the incompatible changes that seem to plague more modern languages
- Scheme has first-class continuations, which I believe Lua doesn't have. In a nutshell, first-class continuations allow you to break the call-return control flow; you can return as many times as you like, or not at all. This is a very flexible feature, which can be used to implement certain things very concisely and elegantly.
- Standard Scheme does not contain structures or objects as found in other languages. Many Scheme implementations support these, or allow one to implement support using macros, but programs that use these features won't be completely compatible with all Scheme implementations.
- Scheme is used extensively in programming language and compiler research. It's also used to teach programming in a number of universities. Scheme is covered in various books, many of which can be read online.
I think that about sums it up. Note that I'm not saying anything is wrong with Lua, I'm just pointing out that Scheme is worth looking into, as well.
For more information, schemers.org is a good place to start.
Please correct me if I got my facts wrong.
What a pointless article. I can summarise it (removing all the grammatical mistakes, and incorrect facts):
/. instead and hope someone posts something useful for a change..
"Some games can be extended with Lua."
Wow! Cos, like, I'd never noticed any of my WoW addons using Lua, and never opened any of the files in curiosity. No...
Anyway. Anyone who actually uses Lua out there? What's a good site with a tutorial on how to develop an addon, or just an intro to the language? Sure, I can google, but with an article like this I'd expect a little more info for the 'hardcore' alongside such a fluffy, wussy introduction, so I'll just rant on
"Frag the weak, hurdle the dead, and assassinate those cursed snipers."