Compiling Quake 3 Virtual Machines To JavaScript

http://www.inolen.com/articles/compiling-quake-3-virtual-machines-to-javascript/

by mariuz • 12 years ago

100 31 12 years ago

inolen.com

webbedhands• 12 years ago

What is up with that comment?

sho_hn• 12 years ago

It's the guy writing TempleOS. Google around, you're in for an interesting story.

itry• 12 years ago

Does he have a new hn account? I love to read his stuff. But the account "losethos" has been inactive for over a month now.

TazeTSchnitzel2• 12 years ago

https://web.archive.org/web/20130629121009/http://qaa.ath.cx...

_random_• 12 years ago

'Transpiling' since it kind of converts to a scripting language not a native code.

pacala3• 12 years ago

asm.js is portable assembly with a jit assembler. In that sense, it's even closer to "native code" than C, as C requires a separate compilation step.

Pacabel2• 12 years ago

That's not true at all.

Asm.js is just a subset of JavaScript that is far more machine-friendly than it is human-friendly. Having a worse syntax than C or normal JavaScript doesn't mean that it's closer to native code or anything like that.

And the compilation step is still there in both cases. It doesn't matter if it's just-in-time compilation or ahead-of-time compilation; it's still compilation, and it's still there.

eliasmacpherson3• 12 years ago

I am confused, there are JIT compilers for C:

http://code.google.com/p/asmjit/

http://homepage1.nifty.com/herumi/soft/xbyak_e.html

How is asm.js different to those?

TazeTSchnitzel2• 12 years ago

Transpiling is also known as source-to-source compilation.

cliffbean• 12 years ago

To add to this, transpiling is a kind of compiling where the source code and target code have roughly the same level of abstraction. asm.js does appear to be more "low-level" than quake bytecode, so this is compiling, and not transpiling.

jahewson• 12 years ago

'Translation' would be the word of choice from PL literature. But there's such a significant transformation going on here that compiling seems quite apt.

ItendToDisagree• 12 years ago

This is pretty crazy impressive! The performance gain particularly. Is that much of a gain expected?

ori_b• 12 years ago

I'm impressed, but I'm not particularly surprised. The initial code was interpreted, while the new code is JIT compiled. I have no data to back this up, but I suspect that if instead of generating javascript, he generated x86 assembly, you'd see a similar speedup. Possibly a larger one.

Scaevolus• 12 years ago

That's exactly what Quake3 did natively, and it gave a large performance boost.

jevinskie• 12 years ago

It would be cool if it compiled either LCC assembly or QVM bytecode to LLVM IR. Now you have all of LLVM's optimizations! Finally, spit out the JS using Emscripten like the rest of the project.

inolen12• 12 years ago

I actually did that first: https://github.com/inolen/qvmc

It worked, but the main issue was related to object file generation.

Basically, you have to allocate one big i8 array to represent all of the QVM's data segments (including its bss segment). This doesn't translate well once compiled with Emscripten, as bss relocation is on a per-variable basis. For one of the Quake 3 Fortress QVMs which was only a few hundred kb it output a ~50mb .bc file and a ~70mb .js file of mostly 0s.

I experimented with storing each segment as its own i8 array (which could be 0 initialized for the bss segment) in a packed struct, which significantly lowered the .bc file size. However, while I was looking into what I'd need to change in Emscripten to support this, I instead decided to go the route of writing the runtime compiler.

Fun fact: Quake 3 mods didn't have access to malloc / free, so it wasn't uncommon to have large amounts of static, 0 initialized data.

ris2• 12 years ago

I thought that too, but remember this has to all be done at runtime, so depending on LLVM would require an Emscripten-ized version of LLVM (does such a thing exist?) to be distributed with the generated js and similarly depending on Emscripten would require a copy of Emscripten to be distributed with the generated js. And from what I hear the runtime performance of Emscripten itself ain't that great.

derefr• 12 years ago

Why does this have to be done at runtime, exactly? How many mods (or rather, QVM files) were there? And are people still making them?

If the answer is "less than 100K" and "no, of course not," then you can probably get away with:

1. compiling all the QVM files to their Javascript equivalents ahead-of-time;

2. stuffing them all on a CDN (with each JS blob named after the md5 of the relevant QVM source);

and then 3. having a "compiler" in your client that just hashes the source it's about to "compile", and requests the blob with that hash from your CDN.

Of course, if the amount of generated JS is small enough, you could even just serve it all with the client. I'm doubting that one, though; it's probably at least 50MB of code. (Though it might be heavily redundant code... it could compress very well!)

cgdangelo• 12 years ago

Very nice. Glad to see CPMA in there. :-)

Compiling Quake 3 Virtual Machines To JavaScript

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