Ignition Gazebo supports choosing what physics engine to use at runtime. This is made possible by Gazebo Physics' abstraction layer.
Ignition Gazebo uses the DART physics engine by default.
Downstream developers may also integrate other physics engines by creating new Gazebo Physics engine plugins. See Gazebo Physics's tutorials to learn how to integrate a new engine.
How Gazebo finds engines
Ignition Gazebo automatically looks for all physics engine plugins that are installed with Ignition Physics. At the moment, that's only DART (ignition-physics-dartsim-plugin).
If you've created a custom engine plugin, you can tell Gazebo where to find it by setting the IGN_GAZEBO_PHYSICS_ENGINE_PATH environment variable to the directory where the plugin's shared library can be found.
For example, if you've created the following physics engine shared library on Linux:
/home/physics_engines/libCustomEngine.so
You should set the variable as follows:
export IGN_GAZEBO_PHYSICS_ENGINE_PATH=/home/physics_engines
If you have several libraries installed in different paths, you can add more paths, for example:
export IGN_GAZEBO_PHYSICS_ENGINE_PATH=/home/physics_engines:/home/more_engines
Tell Gazebo what engine to load
There are a few different ways of telling Gazebo which engine to load.
For any method, you should provide the name of your plugin's shared library, but the lib prefix and the file extension are optional. So in this example, the file is libCustomEngine.so but it's enough to set CustomEngine.
From SDF
You can tell Gazebo what engine to load from the SDF world file by giving the shared library name to the Physics plugin tag.
For the example above, you can load it like this:
From the command line
Alternatively, you can choose a plugin from the command line using the --physics-engine option, for example:
ign gazebo --physics-engine CustomEngine
From C++ API
All features available through the command line are also available through gz::sim::ServerConfig. When instantiating a server programmatically, a physics engine can be passed to the constructor, for example:
Troubleshooting
Failed to find plugin [libCustomEngine.so]. Have you checked the IGN_GAZEBO_PHYSICS_ENGINE_PATH environment variable?
Ignition Gazebo can't find out where libCustomEngine.so is located.
If that's an engine you believe should be installed with Ignition Physics, check if the relevant plugin is installed.
If that's a 3rd party engine, find where the .so file is installed and add that path to the environment variable as described above.
Unable to load the [/home/physics_engines/libCustomEngine.so] library.
There was some problem loading that file. Check that it exists, that you have permissions to access it, and that it's acually a physics engine plugin.
No plugins with all required features found in library [/home/physics_engines/libCustomEngine.so]
This means that there are plugins on that library, but none of them satisfies the minimum requirement of features needed to run an Ignition Gazebo simulation. Be sure to implement all the necessary features.
Failed to load a valid physics engine from [/home/physics_engines/libCustomEngine.so]
Some engines were found in that library, but none of them could be loaded. Check that the the engines implement all the necessary features.