libGDX Open Dynamics Engine (ODE4J) - physics engine LIBRARY

This is a ODE4J library compatible with all libGDX backends, including GWT. It is based on version 0.4.1 of Open Dynamics Engine for Java.

Version ODE4J 0.5.3 (also GWT compatible) can be found here: https://github.com/antzGames/ode4j

If you want to use ODE4J only on libGDX Desktop/Android/iOS backends then I recommend you use odej4 directly.
However if you want cross platform support (i.e include GWT support) then you need to use this library.

Currently this is the only 3D physics engine option for GWT on libGDX.

How to use in your project

Add the dependency in your core project:

project(":core") {
    ...

    dependencies {
        ...
          api "com.github.antzGames:gdx-ode4j:master-SNAPSHOT"
    }
}

If you are targeting HTML (GWT) you will also need the following:

project(":html") {
    ...
    dependencies {
        ...
        implementation "com.github.antzGames:gdx-ode4j:master-SNAPSHOT:sources"
        implementation "com.github.tommyettinger:formic:0.1.4:sources"
    }
}

and lastly add this to your GdxDefinition.gwt.xml file:

<module>
    ...
    <inherits name="gdx_ode4j" />
    <inherits name="formic" />
    ...
</module>

Runtime examples

Some examples can be found in my gdx-ode4j-examples repository.

Or play with them on itch.io.

2023-07-14.00-06-37.mp4

Math classes

Ode4j has its own math classes similar to libGDX's Vector3, Matrix3, Matrix4, and Quaternion.

I added a math utility class called Ode2GDXMathUtils. Use the following methods to create the libGDX Quaternion from ode4j's QuanternionC or DMatrix3C:

    Quaternion q1 = Ode2GdxMathUtils.getGdxQuaternion(odeQuaternion);  
    Quaternion q2 = Ode2GdxMathUtils.getGdxQuaternion(odeMat3);

In addition ode4j uses double and not float like most of libGDX's math classes.

Limitations

Fixed timesteps

ODE was made to work with fixed timesteps. Do not pass Gdx.graphics.getDeltaTime() to world.quickStep().

The following online ODE HOWTO entry discusses how to incorporate this limitation into a game.

Using vsync=true in your game launch configuration helps, but some people might run at 60hz, while others might run at 50Hz, 75Hz, 144Hz. This means that objects will fall/interact at different speeds on these different refresh rates.

Below is example code that you can use to force physics to only update at a fixed interval (timestep).

public static final float MIN_FRAME_LENGTH = 1f/60f;
        ...

@Override
public void render(float deltaTime){
        timeSinceLastRender += deltaTime;

        // Only compute 60Hz for physics
        if (timeSinceLastRender >= MIN_FRAME_LENGTH) {
            odePhysicsSystem.update(MIN_FRAME_LENGTH);   // My custom class, which eventaully calls world.quickStep(MIN_FRAME_LENGTH)
            timeSinceLastRender -= MIN_FRAME_LENGTH;

            if(timeSinceLastRender > MIN_FRAME_LENGTH)
                timeSinceLastRender = 0;
        }

        ...
}

Performance

I have tried jBullet, PhysX and ODE physics engines with libGDX. ODE is the slowest, and the reason being is that in ODE everything is using double precision.

Known Issues

ODE4J 0.4.2 has some Triangle Mesh (TriMesh) collision detection issues.

The owner of ODE4J has fixed them in ODE4J 0.5.0.

List of fixes/changes between 0.4.2 and 0.5.3 can be found here.

Version ODE4J 0.5.3 can be found here: https://github.com/antzGames/ode4j

Where to get ODE/ode4j documentation and help

ODE official manual: http://ode.org/wiki/index.php/Manual

By far the most useful part is the HOWTO section

ode4j discord channel : https://discord.gg/UFXJcXv2P8 ode4j/Java

ode4j contains also some features that are not present in ODE, such as a ragdoll and heightfields with holes. See ode4j's Wiki.

The ODE forum is useful for questions around physics and general API usage.

The ode4j forum is for problems and functionality specific to ode4j/Java.

There is also the old website, including some screenshots.

Here is a Youtube video of a list of games that used ODE from 2002-2015. You will be suprised how many of your favorite games used this physcis libary.

Versions

ODE4J v0.4.1 and v0.5.3 have been ported. Both are GWT compatible.

Version v0.4.1 GitHub repo: https://github.com/antzGames/gdx-ode4j

Version v0.5.3 GitHub repo: https://github.com/antzGames/ode4j

Where has ODE4J libGDX version been used?

Here are some games and projects and tutorials that have used v0.4.1 of ODE4J for libGDX:

https://github.com/MonstrousSoftware/VehicleTest

https://monstrous-software.itch.io/base-invaders

https://monstrous-software.itch.io/fps-demo

https://antzgames.itch.io/physics-in-a-browser

https://antzgames.itch.io/shotgun-wedding

https://antzgames.itch.io/tank-vs-dinos

3D FPS Tutorial using ODE4J

A full blown tutorial on making a libGDX FPS game using ODE4J can be found here:

Tutorial on creating a 3D game with LibGDX

ODE, ode4j and other Licenses

Licensing & Copyright for ODE and ode4j

This library is under copyright by Tilmann Zäschke (Java port), Russell L. Smith (copyright holder of the original ODE code), Francisco Leon (copyright holder of the original GIMPACT code) and Daniel Fiser (copyright holder of the original libccd).

This library is free software; you can redistribute it and/or modify it under the terms of EITHER: (1) The GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The text of the GNU Lesser General Public License is included with this library in the file LICENSE.TXT. (2) The BSD-style license that is included with this library in the files ODE-LICENSE-BSD.TXT and ODE4j-LICENSE-BSD.TXT.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files LICENSE.TXT, ODE-LICENSE-BSD.TXT, GIMPACT-LICENSE-BSD.TXT, GIMPACT-LICENSE-LGPL.TXT, ODE4J-LICENSE-BSD.TXT and LIBCCD_BSD-LICENSE for more details.

The LICENSE.TXT, ODE-LICENSE-BSD.TXT, GIMPACT-LICENSE-BSD.TXT, GIMPACT-LICENSE-LGPL.TXT, LIBCCD_BSD-LICENSE and ODE4J-LICENSE-BSD.TXT files are available in the source code.

Legal

ode4j: Copyright (c) 2009-2017 Tilmann Zäschke [email protected]. All rights reserved.

Like the original ODE, ode4j is licensed under LGPL v2.1 and BSD 3-clause. Choose whichever license suits your needs.

ode4j contains Java ports of the following software

ODE/OpenDE: Copyright (c) 2001,2002 Russell L. Smith All rights reserved.

GIMPACT (part of ODE/OpenDE): Copyright of GIMPACT (c) 2006 Francisco Leon. C.C. 80087371. email: projectileman(AT)yahoo.com

LIBCCD: Copyright (c) 2010 Daniel Fiser <danfis(AT)danfis.cz>; 3-clause BSD License

Turbulenz Engine: Copyright (c) 2009-2014 Turbulenz Limited; MIT License