ahcorde
commented
3 years ago I started a prototype of ign-gazebo based on the examples/standalone/custom_server. https://github.com/ignitionrobotics/ign-gazebo/tree/ahcorde/pybind11
I converted some few method to make it work:
- Gazebo
- server (
run,has_entityandrunning()methods) - ServerConfig (
setSdfFile()method)
- server (
- Common
- console -> (
Setversositystatic function)
- console -> (
You can try it with the following Python script:
from ignition_gazebo import ServerConfig, Server
from ignition_common import set_verbosity
import time
set_verbosity(4)
server_config = ServerConfig()
server_config.set_sdf_file('rolling_shapes.sdf')
server = Server(server_config)
print('Has entity ', server.has_entity('box', 0))
server.run(False, 10000, False)
while(server.is_running()):
time.sleep(0.1)
Incremental example 1
But I was thinking about how to get some data from the simulation. I thought that I can subscribe to some ignition topic. Then I ported:
- Transport
- Node (
subscribe()method)
- Node (
- Msgs
Pose_vmsg
from ignition_gazebo import ServerConfig, Server
from ignition_common import set_verbosity
from ignition_transport import Node
from ignition_msgs import PoseV
import time
set_verbosity(4)
server_config = ServerConfig()
server_config.set_sdf_file('rolling_shapes.sdf')
server = Server(server_config)
print('Has entity ', server.has_entity('box', 0))
def square(msg):
msg.show()
node = Node()
node.subscribe('/world/shapes/pose/info', square)
server.run(False, 10000, False)
while(server.is_running()):
time.sleep(0.1)Incremental example 2
Then I was thinking about to get values from the msgs in Python, not calling a method that prints everything. Here is where the magic start. I don't know if there is a simpler way to convert types between pybind11 and SWIG.
from ignition_gazebo import ServerConfig, Server
from ignition.math import Vector3d
from ignition_msgs import PoseV
p = PoseV()
print(p.get_size())
print(p.get_names())
print(p.get_poses())
print(p.pose())
print(p.pose().x())
p.set_pose(Vector3d(0, 1, 2))The two key methods are:
set_pose()(Setter): This method require to convert ignition::math::vector3Swig object in to a ignition::math::vector3 in cpp. For this I used res1 = SWIG_ConvertPtr(h.ptr(), &argp1, SWIGTYPE_p_ignition__math__Vector3T_double_t, 0 | 0 );pose()(Getter): This method will return a ignition::math::vector3Swig object in Python. For this I used PyObject * resultobj = SWIG_NewPointerObj((new ignition::math::Vector3< double >(static_cast< const ignition::math::Vector3< double >& >(result))), SWIGTYPE_p_ignition__math__Vector3T_double_t, SWIG_POINTER_OWN | 0 );
These thow functions are defined in pythonPYTHON_wrap.cxx which is automatically generated by SWIG when we create the wrapper for ign-math. I copied partially this file to make it work this example. I know this is a big hack and it's not the path to follow.
Suggestions are welcome
FYI @chapulina @azeey @scpeters
traversaro
diegoferigo
srmainwaring
chapulina
Desired behavior
Gazebo can be used as a library by other programs, like shown on the custom_server example. The Server C++ API can be used to initialize the simulation and step it using the
Runfunction.It would be interesting to expose that functionality through a C API so that it can be eventually wrapped by other scripting languages like Python.
We already have a C API in ign.cc which is used by the command line tool, but we don't expose that to users or keep it stable.
The new C API should be able to do things like starting a server, loading an SDF file, stepping the simulation and retrieving data (entities and components) from it.
Alternatives considered
Instead of adding a C API, we could extend the C++ API to add the desired functionality, and that can be converted to scripting languages using SWIG like we're doing on ign-math.
Implementation suggestion
Before creating the API, it would be interesting to write a concise design doc into https://github.com/ignitionrobotics/design
Additional context
The
gym-ignitionproject is using SWIG to wrap our C++ API, with some sugar on top :candy: