ammo.js

Demos

• Cubes
• Cubes (WebAssembly)
• SoftBody-Rope
• SoftBody-Cloth
• SoftBody-Volume
• Heightmap
• Vehicle

Overview

Example code to give you an idea of the API:

• https://github.com/kripken/ammo.js/blob/master/examples/webgl_demo/worker.js#L6 which interacts with https://github.com/kripken/ammo.js/blob/master/examples/webgl_demo/ammo.html#L14

ammo.js is a direct port of the Bullet physics
engine to JavaScript, using Emscripten. The source
code is translated directly to JavaScript, without human rewriting, so
functionality should be identical to the original Bullet.

Note: ammo.js has just been updated to a new porting approach. If you find
some part of the Bullet API that is not supported that you need, please see
https://github.com/kripken/ammo.js/issues/60

'ammo' stands for "Avoided Making My Own js physics engine by compiling bullet
from C++" ;)

ammo.js is zlib licensed, just like Bullet.

Discussion takes place on IRC at #emscripten on Mozilla's server
(irc.mozilla.org)

Instructions

builds/ammo.js contains a prebuilt version of ammo.js. This is probably what you want.

You can also build ammo.js yourself, as follows:

• Get Emscripten

  http://emscripten.org

  and set it up. See

  http://kripken.github.io/emscripten-site/docs/getting_started/

• Run the build script,

  python make.py

  which should generate builds/ammo.js.

• Optionally, run the automatic tests,

  python test.py

Usage

The most straightforward thing is if you want to write your code in C++, and
run that on the web. If so, then you can build your C++ code with emscripten
normally and either build and link Bullet using

https://emscripten.org/docs/compiling/Building-Projects.html

or you can use Bullet directly from emscripten-ports, with -s USE_BULLET=1.
In both cases, you don't need ammo.js, just plain Bullet.

If, on the other hand, you want to write code in JavaScript, you can use the
autogenerated binding code in ammo.js. A complete example appears in

examples/hello_world.js

That is HelloWorld.cpp from Bullet, translated to JavaScript. Other examples
in that directory might be useful as well. In particular see the WebGL
demo code in

examples/webgl_demo/ammo.html

Bindings API

ammo.js autogenerates its API from the Bullet source code, so it should
be basically identical. There are however some differences and things
to be aware of:

• See https://github.com/kripken/emscripten/wiki/WebIDL-Binder
  for a description of the bindings tool we use here, which includes
  instructions for how to use the wrapped objects.

• All ammo.js elements should be accessed through Ammo.*. For example,
  Ammo.btVector3, etc., as you can see in the example code.

• Member variables of structs and classes can be accessed through
  setter and getter functions, that are prefixed with , get_, or , set_, .
  For example,

  rayCallback.get_m_rayToWorld()

  will get m_rayToWorld from say a ClosestRayResultCallback. Native
  JavaScript getters and setters could give a slightly nicer API here,
  however their performance is potentially problematic.

• Functions returning or getting float& or btScalar& are converted to
  float. The reason is that float& is basically float* with nicer syntax
  in C++, but from JavaScript you would need to write to the heap every
  time you call such a function, making usage very ugly. With this change,
  you can do , new btVector3(5, 6, 7), and it will work as expected. If
  you find a case where you need the float& method, please file an issue.

• Not all classes are exposed, as only what is described in ammo.idl is
  wrapped. Please submit pull requests with extra stuff that you need
  and add.

• There is experimental support for binding operator functions. The following
  might work:, Operator, Name in JS, -----------, ------------, =, op_set, +, op_add, -, op_sub, *, op_mul, /, op_div, [], op_get, ==, op_eq, Reducing Build Size
  ===============

The size of the ammo.js builds can be reduced in several ways:

• Removing uneeded interfaces from ammo.idl. Some good examples of this are btIDebugDraw and DebugDrawer, which are both only needed if visual debug rendering is desired.

• Removing methods from the -s EXPORTED_RUNTIME_METHODS=[] argument in make.py. For example, UTF8ToString is only needed if printable error messages are desired from DebugDrawer.

Troubleshooting

• It's easy to forget to write, new, when creating an object, for
  example

  var vec = Ammo.btVector3(1,2,3); // This is wrong! Need 'new'!

  This can lead to error messages like the following:

  Cannot read property 'a' of undefined
Cannot read property 'ptr' of undefined

  This is an annoying aspect of JavaScript, sadly.

Reporting Issues

If you find a bug in ammo.js and file an issue, please include a script
that reproduces the problem. That way it is easier to debug, and we can
then include that script in our automatic tests.

Release Process

Pushing a new build in builds/ammo.js should be done only after the
following steps:

• Build using python make.py closure which generates the asm.js
  build, and python make.py closure wasm which generates the wasm
  build.

• Make sure it passes all automatic tests using
  python test.py (build-name) Note that it uses SpiderMonkey
  by default, and SPIDERMONKEY_ENGINE is defined in ~/.emscripten,
  see the script contents for details.

• Run the WebGL demo in examples/webgl_demo and make sure it looks
  ok, using something like firefox examples/webgl_demo/ammo.html
  (chrome will need a webserver as it doesn't like file:// urls)

Upstream Version

Bullet 2.82 patched with raycast fix from 2.83