An example of D to asmjs using emscripten
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An example of D to asmjs using Emscripten



This is a demonstration on how D code can be compiled to Javascript using a combination of existing tools.


You can try an online demo here:


  • Fetch and build the toolchains

    $ ./fetch_toolchain

    This will take some time, as it will build LLVM-fastcomp and a patched ldc2. The result will be in the /tmp/toolchains directory. Alternatively, it's possible to specify another installation prefix using the 'PREFIX' environment variable.

    It's also possible to specify another temporary directory using the 'tmpDir' environment variable. Using a tmpfs (in-RAM directory) is recommended, as it greatly speeds up the build.

  • Add some directories to your PATH

    First, add the JSBackend LLVM toolchain. This one provides ldc2, clang, llc.

    $ export PATH=/tmp/toolchains/llvm-js/bin:$PATH

    Then, add Emscripten itself, i.e the python 'emcc' tool family. This relies on the JSBackend LLVM toolchain.

    $ export PATH=/tmp/toolchains/emscripten:$PATH
  • Check your PATH:

    Here's what you should get:

    $ which -a llvm-config

    If you have more than one llvm-config appearing in this list, you're asking for trouble and the build might not work.

  • Now configure emscripten. This will create a '.emscripten' configuration file in your home, containing the path to LLVM 3.9svn (aka 'fastcomp', which implements the JSBackend). "emcc" will use this path to find its Javascript-enabled clang and llc.

    rm -f ~/.emscripten
    EMMAKEN_JUST_CONFIGURE=1 PATH=/tmp/toolchains/llvm-js/bin:$PATH /tmp/toolchains/emscripten/emcc
  • Run the build script (it just sets some variables before calling the makefile)

    $ ./build_asmjs

    (If it fails, try removing ~/.emscripten, or setting EM_CONFIG to anything else)

  • Enjoy the result:

    $ firefox bin/asmjs/game.html
  • You can also play the native version:

    $ ./build_native
    $ ./bin/native/game.exe


  • The build scripts and demo game source files are licensed under the GNU Affero GPL. In short: you're free to run them for whatever purpose, but if you put them on a server and provide them as a service, you must ensure your users have access to the source code, under the same license.

  • Everything under the '/rt' directory is licensed under the permissive Boost software license. Indeed, some parts of 'rt' get integrated to the produced asm.js binaries, for which I don't want to impose any restriction.