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.
'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)
builds/ammo.js contains a prebuilt version of ammo.js. This is probably what you want.
You can also build ammo.js yourself.
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
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_rayToWorldfrom say aClosestRayResultCallback. Native JavaScript getters and setters could give a slightly nicer API here, however their performance is potentially problematic. -
Functions returning or getting
float&orbtScalar&are converted to float. The reason is thatfloat&is basicallyfloat*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
In order to build ammo.js yourself, you will need Emscripten and cmake.
For more information about setting up Emscripten, see the getting started guide.
To configure and build ammo into the builds directory, run the following:
$ cmake -B builds
$ cmake --build buildsThere are also some key options that can be specified during cmake configuration, for example:
$ cmake -B builds -DCLOSURE=1 # compile with closure
$ cmake -B builds -DTOTAL_MEMORY=268435456 # allocate a 256MB heap
$ cmake -B builds -DALLOW_MEMORY_GROWTH=1 # enable a resizable heapOn windows, you can build using cmake's mingw generator:
> cmake -B builds -G 'MinGW Makefiles'
> cmake --build buildsNote that if you have not installed emscripten via the emsdk, you can configure
its location with -DEMSCRIPTEN_ROOT.
ammo.js can also be built with Docker. This offers many advantages (keeping its native environment clean, portability, etc.). To do this, you just have to install Docker and run:
$ docker-compose build # to create the Docker image
$ docker-compose up # to create the Docker container and build ammo.js
$ docker-compose run builder # to build again the ammojs targets after any modificationIf you want to add arguments to cmake, you have to edit the docker-compose.yml file.
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
btIDebugDrawandDebugDrawer, 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,UTF8ToStringis only needed if printable error messages are desired fromDebugDrawer.
You can run the automatic tests with npm test, which in turn will run ava against both the javascript and WebAssembly builds:
$ npm run test-js # --> AMMO_PATH=builds/ammo.js ava
$ npm run test-wasm # --> AMMO_PATH=builds/ammo.wasm.js avaIt's also possible to run ava directly for more options:
$ npx ava --verbose
$ npx ava --node-arguments inspect
When no AMMO_PATH is defined, builds/ammo.js is tested by default.
http-server is included as a dev
dependency as an easy way to run the examples. Make sure to serve everything
from the repo root so that the examples can find ammo in the builds
directory:
$ npx http-server -p 3000 .-
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 undefinedCannot read property 'ptr' of undefinedThis is an annoying aspect of JavaScript, sadly.
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.
Pushing a new build in builds/ammo.js should be done only after the
following steps:
-
Configure with closure enabled:
cmake -B builds -DCLOSURE=1 -
Build both the asm.js and wasm libraries:
cmake --build builds -
Make sure they pass all automatic tests:
npm test -
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)
Bullet 2.82 patched with raycast fix from 2.83
![dependabot[bot] avatar](https://avatars.githubusercontent.com/in/29110?v=4 "dependabot[bot]")
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