Messaging/interfaces/connectivity

There are several ways messages or data can be exchanged/transmitted/received in and around CoppeliaSim. One can exchange data within CoppeliaSim, via:

signals

custom data blocks

calling plugin functions

Data can also be exchanged with an external application, other computer, machine, etc., via:

calling script functions

Signals

Signals can be seen as global variables. They can be defined, redefined, read and cleared. For example:

-- script 1 writes the data to string signal mySignalName:

local myData={1,2,{"Hello","world",true,{value1=63,value2="aString"}}}
sim.setStringSignal("mySignalName",sim.packTable(myData))

-- script 2 reads the data from string signal mySignalName:

local myData=sim.getStringSignal("mySignalName")
if myData then
    myData=sim.unpackTable(myData)
end

Custom data blocks

Custom data blocks is data that is stored inside of a scene object, or inside a scene. It can be used to store custom data to be saved together with a model or scene, but also as a means of communication. For example:

-- script 1 writes the data to the scene:

local myData={1,2,{"Hello","world",true,{value1=63,value2="aString"}}}
sim.writeCustomDataBlock(sim.handle_scene,"myTag",sim.packTable(myData))

-- script 2 reads the data from the scene:

local myData=sim.readCustomDataBlock(sim.handle_scene,"myTag")
if myData then
    myData=sim.unpackTable(myData)
end

Calling plugin functions

Scripts can call specific plugin functions, so-called callback functions: in order to be able to do this, the plugin must first register its callback functions via simRegisterScriptFunction. This is a convenient mechanism to extend CoppeliaSim's functionality, but can also be used for complex data exchange between scripts and plugins. Following illustrates a very simple plugin function and its registration:

void myCallbackFunc(SScriptCallBack* p)
{
    int stack=p->stackID;
    CStackArray inArguments;
    inArguments.buildFromStack(stack);
	
    if ( (inArguments.getSize()>0)&&inArguments.isString(0) )
    {
        std::string tmp("we received a string: ");
        tmp+=inArguments.getString(0);
        simAddLog("ABC",sim_verbosity_msgs,tmp.c_str());
		
		CStackArray outArguments;
		outArguments.pushString("Hello to you too!");
		outArguments.buildOntoStack(stack);
    }
    else
        simSetLastError("simABC.func","Not enough arguments or wrong arguments.");
}

// Somewhere in the plugin's initialization code:
simRegisterScriptCallbackFunction("simABC.func@ABC","string reply=simABC.func(string inputStr)",myCallbackFunc);

Calling script functions

A script function can obviously be called from within the same script, but also:

across scripts (via sim.callScriptFunction)

from a plugin (via simCallScriptFunctionEx)

from a ROS client (via a callback mechanism)

or from a remote API client (via simxCallScriptFunction (legacy remote API) and simxCallScriptFunction (B0-based remote API)

The called script function can perform various tasks, then send back data to the caller. This is also a simple way to extend the functionality of an external application in a quick manner. It is however important that the called script doesn't perform lengthly tasks, otherwise everything will come to a halt (lengthly tasks should rather be triggered externally, and processed at an appropriate moment by the script itself when called from the regular system callbacks).

ZMQ

The ZeroMQ library, wrapped inside the ZMQ plugin, offers several API functions related to ZeroMQ messaging. Following illustrates a simple requester:

function sysCall_init()
    corout=coroutine.create(coroutineMain)
end

function sysCall_actuation()
    if coroutine.status(corout)~='dead' then
        local ok,errorMsg=coroutine.resume(corout)
        if errorMsg then
            error(debug.traceback(corout,errorMsg),2)
        end
    end
end

function coroutineMain()
    printf('Connecting to hello world server...')
    context=simZMQ.ctx_new()
    requester=simZMQ.socket(context,simZMQ.REQ)
    simZMQ.connect(requester,'tcp://localhost:5555')

    for request_nbr=0,10 do
        print('-----------------------------------------')
        local data='Hello'
        printf('[requester] Sending "%s"...',data)
        simZMQ.send(requester,data,0)
        local rc,data=simZMQ.recv(requester,0)
        printf('[requester] Received "%s"',data)
    end
end

function sysCall_cleanup()
    simZMQ.close(requester)
    simZMQ.ctx_term(context)
end

And following would be the corresponding responder:

function sysCall_init()
    corout=coroutine.create(coroutineMain)
end

function sysCall_actuation()
    if coroutine.status(corout)~='dead' then
        local ok,errorMsg=coroutine.resume(corout)
        if errorMsg then
            error(debug.traceback(corout,errorMsg),2)
        end
    end
end

function coroutineMain()
    context=simZMQ.ctx_new()
    responder=simZMQ.socket(context,simZMQ.REP)
    local rc=simZMQ.bind(responder,'tcp://*:5555')
    if rc~=0 then error('failed bind') end
    
    while true do
        local rc,data=simZMQ.recv(responder,0)
        printf('[responder] Received "%s"',data)
        data='World'
        printf('[responder] Sending "%s"...',data)
        simZMQ.send(responder,data,0)
    end
end

function sysCall_cleanup()
    simZMQ.close(responder)
    simZMQ.ctx_term(context)
end

ROS

Using ROS or ROS2, one can communicate with the outside world, but also within CoppeliaSim. For example, a vision sensor ROS2 publisher could look like:

function sysCall_init()
    visionSensor=sim.getObjectHandle('Vision_sensor')

    -- Enable an image publisher:
    pub=simROS2.createPublisher('/image', 'sensor_msgs/msg/Image')
    simROS2.publisherTreatUInt8ArrayAsString(pub)
end

function sysCall_sensing()
    -- Publish the image of the vision sensor:
    local img,w,h=sim.getVisionSensorCharImage(visionSensor)
    data={}
    data.header={stamp=simROS2.getTime(), frame_id='a'}
    data.height=h
    data.width=w
    data.encoding='rgb8'
    data.is_bigendian=1
    data.step=w*3
    data.data=img
    simROS2.publish(pub,data)
end

function sysCall_cleanup()
    simROS2.shutdownPublisher(pub)
end

The subscriber on the other hand could look like:

function sysCall_init()
    -- Enable an image subscriber:
    sub=simROS2.createSubscription('/image', 'sensor_msgs/msg/Image', 'image_callback')
    simROS2.subscriptionTreatUInt8ArrayAsString(sub)
end

function image_callback(msg)
    -- Here we have received an image
end

function sysCall_cleanup()
    simROS2.shutdownSubscription(sub)
end

Remote API

Using the legacy remote API, or the B0-based remote API, one can communicate with the outside world, but also within CoppeliaSim. For example, a Python legacy remote API client receiving and applying back a vision sensor image could look like:

import sim
from time import sleep
clientID=sim.simxStart('127.0.0.1',19997,True,True,5000,5)
if clientID!=-1:
    res,sensor1Handle=sim.simxGetObjectHandle(clientID,'VisionSensor1',sim.simx_opmode_oneshot_wait)
    res,sensor2Handle=sim.simxGetObjectHandle(clientID,'VisionSensor2',sim.simx_opmode_oneshot_wait)

    res,resolution,image=sim.simxGetVisionSensorImage(clientID,sensor1Handle,0,sim.simx_opmode_streaming)
    sim.simxStartSimulation(clientID,sim.simx_opmode_oneshot)
    while (sim.simxGetConnectionId(clientID)!=-1):
        res,resolution,image=sim.simxGetVisionSensorImage(clientID,sensor1Handle,0,sim.simx_opmode_buffer)
        if res==sim.simx_return_ok:
            res=sim.simxSetVisionSensorImage(clientID,sensor2Handle,image,0,sim.simx_opmode_oneshot)
        sleep(0.01)
    sim.simxFinish(clientID)

The same example as above, but for a B0-based remote API client:

import b0RemoteApi
from time import sleep
with b0RemoteApi.RemoteApiClient('b0RemoteApi_pythonClient','b0RemoteApi') as client:    
        
    def imageCallback(msg):
        client.simxSetVisionSensorImage(sensor2Handle[1],False,msg[2],client.simxDefaultPublisher())
    
    sensor1Handle=client.simxGetObjectHandle('VisionSensor1',client.simxServiceCall())
    sensor2Handle=client.simxGetObjectHandle('VisionSensor2',client.simxServiceCall())
    client.simxGetVisionSensorImage(sensor1Handle[1],False,client.simxDefaultSubscriber(imageCallback))
    client.simxStartSimulation(client.simxDefaultPublisher())
    while True: 
        client.simxSpinOnce()
        sleep(0.01)
    client.simxStopSimulation(client.simxDefaultPublisher())

BlueZero

Using BlueZero, one can communicate with the outside world, but also within CoppeliaSim. For example, a vision sensor publisher could look like:

function sysCall_init()
    visionSensor=sim.getObjectHandle('Vision_sensor')

    -- Enable an image publisher:
    b0Node=simB0.nodeCreate('b0Node')
    pub=simB0.publisherCreate(b0Node,'image')
    simB0.nodeInit(b0Node)
end

function sysCall_sensing()
    -- Publish the image of the vision sensor:
    local msg=sim.getVisionSensorCharImage(visionSensor)
    simB0.publisherPublish(pub,msg)
end

function sysCall_cleanup()
    if b0Node then
        simB0.nodeCleanup(b0Node)
        simB0.publisherDestroy(pub)
        simB0.nodeDestroy(b0Node)
    end
end

The subscriber on the other hand could look like:

function sysCall_init()
    -- Enable an image subscriber:
    b0Node=simB0.nodeCreate('b0Node')
    sub=simB0.subscriberCreate(b0Node,'image','image_callback')
    simB0.nodeInit(b0Node)
end

function image_callback(msg)
    -- Here we have received an image
end

function sysCall_sensing()
    simB0.nodeSpinOnce(b0Node)
end

function sysCall_cleanup()
    if b0Node then
        simB0.nodeCleanup(b0Node)
        simB0.subscriberDestroy(sub)
        simB0.nodeDestroy(b0Node)
    end
end

Serial port

CoppeliaSim implements several serial port API functions.

LuaSocket

CoppeliaSim ships with the LuaSocket extension library. Following illustrates how to fetch a webpage:

http=require('socket.http')
page=http.request('http://www.google.com')