Emscripten 1.2, Doom on the Web

Emscripten, the LLVM to JavaScript compiler, is now at version 1.2. The main updates in this release were to enable this demo of Doom on the Web - a playable version of the classic game Doom, compiled from C to JavaScript and rendering using Canvas.

The demo is known to work on Firefox and Safari. It works, but slowly, on Opera. I can't get it to run properly in Chrome due to a problem with V8. I have no idea if it runs on IE9, since I don't have a Windows machine, but since IE9 has a fast JS engine and supports canvas, it should (please let me know if you try it there). Edit: Here's a screencast of the demo running on Firefox Nightly if you can't run it yourself.

Highlights of Emscripten 1.2:

• Many improvements to Emscripten's implementation of the SDL API in JavaScript, including support for color palettes (Doom uses a 256-color palette), input events (we translate normal web keyboard events into their SDL forms), and audio (for now, just using the Mozilla Audio Data API - it's the most straightforward API at this point. Patches are welcome for other ones).
• Many improvements to the CHECK_* and CORRECT_* options, which are very important for generating optimized code using Emscripten. In particular, there is a new AUTO_OPTIMIZE option which will output a summary of which checks ran how any times, and how many of those checks failed, giving you a picture of which lines are important to be optimized, and which can be.
• Some additional experimental work is ongoing about supporting OpenGL in WebGL. I don't know either OpenGL or WebGL very well, I'm learning as I go, and I'm not sure how feasible this project is. If you can help here, please do!
• Various bug fixes. Thanks to all the people that submitted bug reports. In addition compiling Doom uncovered a few small bugs, for example we were not doing bit shifts on 64-bit integers properly.

Emscripten 1.0!

It's been almost a year since I started Emscripten (which, if you haven't heard of it, is a tool to compile LLVM to JavaScript), during which it took up much of my spare time. So I am very pleased to announce that today Emscripten has reached the 1.0 milestone. This release comes with a demo of rendering PDFs on the web (warning: that page downloads >12MB, since it includes Poppler and FreeType. It's like downloading an entire desktop app, almost).

Other highlights in this release:

• Very significant optimization of memory use in the compiler. This was necessary for the PDF demo to build, since it is far larger than previous demos.
• Full support for the recently released LLVM 2.9.
• The Emscripten documentation paper is finished. It explains how Emscripten works, so you might be interested in it if you care what Emscripten does under the hood (but if you just want to use Emscripten you don't need to read it).

Overall Emscripten is now in very good shape. It can probably compile most any C/C++ project out there, subject to some limitations (like JS not allowing C-style multithreading). At times some manual intervention is needed, like changing the project's settings so it doesn't generate inline assembly, and of course bugs probably still exist, but recently the code I have compiled has tended to just work (hence the rate of commits has greatly decreased recently).

The speed of the generated code can be quite good. By default Emscripten compiles with very conservative settings, so the code will be slow, but optimizing the code is not that hard to do. Optimized code tends to run around 10x slower than gcc -O3, which is obviously not great, but on the other hand fairly decent and more than good enough for many purposes. And of course, that ratio will improve along with advancements in JavaScript engines, LLVM, and the Closure Compiler.

So, Emscripten 1.0 is in my opinion pretty solid. There are no major outstanding bugs, and no major missing features. (But I do have plans for some major improvements, which are difficult, but should end up with code that runs at least twice as fast.) Now that Emscripten is at 1.0, I am hoping to see it used in more places. I'm starting to propose at Mozilla that we use it in various ways, and also I'd love to see things like GTK or Qt ported to the web - if anyone wants to collaborate on that, let me know.

LIL browser demo

I just saw this demo of LIL (a Little Interpreted Language) running in the browser, compiled from C to JavaScript using Emscripten. Cool stuff!