Connecting to An Exercise

The program creates an exercise connection (DtExerciseConn.) This connection serves as the program's interface to an exercise. DtExerciseConn has several constructors. In this example, we create a DtVrlApplicationInitializer and pass it to the DtExerciseConn. Use of a DtVrlApplicationInitializer provides support for command line arguments. The default protocol-specific initialization values are set in the DtVrlApplicationInitializer and its base class, DtExerciseConnInitializer. This is the only protocol-specific part of the code.

Managing State and Interaction Information

Applications based on VR-Link typically use callbacks to handle incoming interactions such as fire, detonations, and collisions. For example, a callback named fireCb is registered with the DtFireInteraction class. This callback prints a message containing the attacker ID. It executes whenever the exercise connection receives a Fire PDU or interaction during a call to drainInput().

Tracking Entities

We create a reflected entity list to keep track of entities found on the network. The entity list tracks the arrival and departure of entities, performs dead reckoning, manages time outs, and performs other entity-tracking tasks.

Time Managing Time

We obtain a pointer to the simulation clock from the exercise connection.

Listening to the Network

At the start of each iteration, the program sets VR-Link simulation time to provide a common time value for use by time-related operations that occur within an iteration of the loop (such as the dead-reckoning of multiple entities.) The drainInput() call reads and processes any messages arriving through the exercise connection. This call triggers the execution, if needed, of any callbacks you have registered for that exercise connection.

The program finds the first entity in the entity list, then it retrieves the pointer to the entity's entity state repository. It creates a topographic view of that entity state repository, allowing us to retrieve its position data in topographic coordinates rather than geocentric. (The coordinates for this example are hard-coded.) The application obtains and prints the dead-reckoned entity location.

Example Code

/****************************************************************************
 * Copyright (c) 2017 MAK Technologies, Inc
 * All rights reserved.
 ****************************************************************************/
#include <vl/exerciseConn.h>
#include <vl/exerciseConnInitializer.h>
#include <vl/reflectedEntityList.h>
#include <vl/entityStateRepository.h>
#include <vl/reflectedEntity.h>
#include <vl/fireInteraction.h>
#include <vl/topoView.h>
#include <vl/fomMapper.h>
#include <vl/environmentProcessRepository.h>
#include <vl/reflectedEnvironmentProcess.h>
#include <vl/reflectedEnvironmentProcessList.h>
#include <vl/signalInteraction.h>
#include <vlutil/vlProcessControl.h>
#include <vlutil/vlMiniDumper.h>
#include <vlutil/vlStringUtil.h>
#include <vlutil/vlSimpleKeyboard.h>
#include <iostream>
DtSimpleKeyboard input;
int theReceivedUpdateCount = 0;
void DtRtiShutdownHandler(const char * label, void* finished)
{
   //This callback may occur multiple times, since it gets called
   //every time we make an RTI call with an error. So, we mark this
   //as finished and make sure that we only signal once.
   int* finishedInt = (int*)finished;
   if (*finishedInt)
   {
      DtWarn << "Shutting down: " << label << std::endl;
   }
   *finishedInt = 0; //Order a shutdown;
}
// A callback for when a DtReflectedEnvironmentProcess object is updated.
void printEnvProc(DtReflectedEnvironmentProcess* obj, void* userData)
{
   obj->epsr()->printData();
   theReceivedUpdateCount++;
}
// A callback for when a new DtReflectedEnvironmentProcess object is added.
void envProcAddedCb(DtReflectedEnvironmentProcess* obj, void* userData)
{
   // register a callback for when an existing object is updated.
   obj->addPostUpdateCallback(printEnvProc, userData);
}
// A callback for when a DtReflectedEntity object is updated.
void entityUpdateCount(DtReflectedEntity* obj, void* userData)
{
   theReceivedUpdateCount++;
}
// A callback for when a new DtReflectedEntity object is added.
void entityAddedCb(DtReflectedEntity* obj, void* userData)
{
   // register a callback for when an existing object is updated.
   obj->addPostUpdateCallback(entityUpdateCount, userData);
}
//Criteria function checks object's entity type before allowing discovery
//Will do the same as the discoverOnlyWhenEntityTypeKnown, but modifiable 
bool criteria(DtReflectedObject* obj, void* usr)
{
    DtReflectedEntity* ent = (DtReflectedEntity*)obj;
    //Use this line to make custom criteria for delayed object discovery.
    if (ent->esr()->entityType() == DtEntityType(0, 0, 0, 0, 0, 0, 0))
    {
        return false;
    }
    return true;
}
// Define a callback to process fire interactions.
void fireCb(DtFireInteraction* fire, void* /*usr*/)
{
   std::cout << "Fire Interaction from " <<  fire->attackerId().string() << std::endl;
}
void sigCb(DtSignalInteraction* sig, void* /*usr*/)
{
}
int main(int argc, char** argv)
{
   DtINIT_MINIDUMPER( "Listen" );
   try
   {
      // Create an exercise conn initializer. This will parse the command
      // line, as well as parse an mtl file with the same name as this application.
      DtVrlApplicationInitializer appInit(argc, argv, "VR-Link Listen");
#if DtDIS
      // Please note, this is the only protocol specific code in this example. For
      // HLA there is no network connection, so there is no concept of AsyncIO at the
      // VR-Link level.
      appInit.setUseAsynchIO( true );
      appInit.setDisVersionToSend( 7 );
#else
      // Set the default FED File, executable, and version
      appInit.setFedFileName( DtDefaultRpr2Fom );
      appInit.setExecName( "MAK-One-2024" );
      appInit.setRprFomVersion( 2.0 );
      appInit.setRprFomRevision( 2 );
#ifdef DtHLA_1516_EVOLVED
      std::vector<DtString> fomModules;
      std::vector<DtString> fomModuleFromCommandLine;
      appInit.fomModules(fomModuleFromCommandLine);
      fomModules.push_back("NETN-BASE.xml");
      fomModules.push_back("NETN-Physical.xml");
      fomModules.push_back("NETN-METOC.xml");
      fomModules.push_back("NETN-MRM.xml");
      fomModules.push_back("MAK-Physical-2_evolved.xml");
      fomModules.push_back("MAK-Aerodrome-1_evolved.xml");
      fomModules.push_back("MAK-METOC-1_evolved.xml");
      fomModules.push_back("MAK-VRFExt-9_evolved.xml");
      fomModules.push_back("MAK-DIGuy-7_evolved.xml");
      fomModules.push_back("MAK-LgrControl-2_evolved.xml");
      fomModules.push_back("MAK-VRFAggregate-6_evolved.xml");
      fomModules.push_back("MAK-DynamicTerrain-2_evolved.xml");
      fomModules.push_back("MAK-VRLExt-3_evolved.xml");
      fomModules.push_back("MAK-DER-1_evolved.xml");
      fomModules.push_back("RPR-Enumerations_Experimental_IFF.xml");
      fomModules.push_back("RPR-MAK_Experimental_IFF-3.xml");
      fomModules.insert(fomModules.end(), fomModuleFromCommandLine.begin(), fomModuleFromCommandLine.end());
      appInit.setFomModules(fomModules);
#endif
#endif
      // Process the command line. This will actually set values in the
      // DtVrlApplicationInitializer class and should be called before
      // creating the DtExerciseConn instance.
      appInit.parseCmdLine();
      DtExerciseConn::InitializationStatus status = DtExerciseConn::DtINIT_SUCCESS;
      // The DtExerciseConn instance is perhaps the most important class
      // in any VR-Link exercise. Think of it as the hub which holds
      // everything else together. Technically this instance is what's
      // responsible for connecting this federate to another federate via
      // a network, or an RTI. After exConn is created, and if no error
      // has occurred this simulator will be a live federate.
      DtExerciseConn exConn(appInit, &status);
      // Initialize VR-Link time.
      DtClock* clock = exConn.clock();
#ifdef DtHLA
      // Let other VR-Link federates know that we are initializing
      // Helps control request update calls when creating many entities
      // Requests are delayed until all federates are initialized or executing
      std::cout << "[" << clock->simTime() << ",  " << " 0] Initializing" << std::endl;
      exConn.setExecutionStatus(vrlstatus_initializing);
      exConn.drainInput(0.1);
#endif
      if (status != 0)
      {
         std::cout << "Error creating exercise connection." << std::endl;
         return -1;
      }
      DtReflectedEnvironmentProcessList relEnv(&exConn);
      relEnv.addEnvironmentProcessAdditionCallback(envProcAddedCb, NULL);
      // Register a callback to handle fire interactions.
      DtFireInteraction::addCallback(&exConn, fireCb, NULL);
      DtSignalInteraction::addCallback(&exConn, sigCb, NULL);
      // Create an object to manage entities that we hear about on the network.
      DtReflectedEntityList rel(&exConn);
      rel.addEntityAdditionCallback (entityAddedCb, NULL);
      //Attaching criteria function to DtReflectedEntityList
      //for delayed object discovery.
      rel.setDiscoveryCondition(criteria, NULL);
#ifdef DtHLA
      // Let other VR-Link federates know that we are executing
      std::cout << "[" << clock->simTime() << ",  " << " 0] Executing" << std::endl;
      exConn.setExecutionStatus(vrlstatus_executing);
      exConn.drainInput(0.1);
#endif
      int forever = 1;
#ifdef DtHLA
      //Shutdown handler in order to smoothly end if the HLA exercise shuts down
      exConn.addRtiErrorCb(&DtRtiShutdownHandler, &forever);
#endif
      unsigned long loopCount = 0;
      DtTime outputTime = 0.0;
      double outputInterval = appInit.outputInterval();
      double frameTime = 0.1;
      clock->init();
      std::cout << std::fixed << std::setprecision(2);
      while (forever)
      {
         DtTime startTime = clock->elapsedRealTime();
         // Tell VR-Link the current value of simulation time.
         clock->setSimTime(startTime);
         loopCount++;
         // Check if user hit 'q' to quit.
         if (input.keybrdTick() == -1)
            break;
         // Find the first entity in the reflected entity list.
         DtReflectedEntity *first = rel.first();
         if (first && (outputInterval <= 0.0 || outputTime < clock->absRealTime()))
         {
            // Grab its state repository, where we can inspect its data.
            DtEntityStateRepository *esr = first->entityStateRep();
            esr->printData();
#if DtDIS
            const char* entityId = first->entityId().string();
#else
            const char* entityId = first->globalId().string();
#endif
            // Create a topographic view on the state repository, so we
            // can look at position information in topographic coordinates.
            double refLatitude  = DtDeg2Rad(  35.699760);
            double refLongitude = DtDeg2Rad(-121.326577);
            DtTopoView topoView(esr, refLatitude, refLongitude);
            // Print some listen stats and some info from first entity.
            // Could use location string for printing but since its topo view, only need precision of 2 that we set above.
            std::cout << "[" << clock->simTime() << ", " << loopCount << "] #entities: " << rel.count()
               << " #updates received: " << theReceivedUpdateCount << ", "
               << "First entity: \"" << entityId << "\" " << " position: "
               << "(" << topoView.location().x() << ", " << topoView.location().y() << ", " << topoView.location().z() << ")" << std::endl;
            theReceivedUpdateCount = 0;
            outputTime = clock->absRealTime() + outputInterval;
         }
         DtTime duration = clock->elapsedRealTime() - startTime;
#ifdef DtDIS
         // Process any incoming messages if available for up to max interval
         // Drain input will return early if there is no input.
         exConn.drainInput(frameTime - duration);
         duration = clock->elapsedRealTime() - startTime;
         if (duration < frameTime)
         {
            // Sleep for the remaining frame time
            DtSleep(frameTime - duration);
         }
#else
         // Process any incoming messages for up to 1st max interval but at least for the 2nd min interval.
         // Drain input will sleep and wakeup internally for input while waiting for the minimum interval to expire
         // so the max and min intervals govern the frame time minus the time it took to print above.
         exConn.drainInput(frameTime - duration, frameTime - duration);
#endif
      }
   }
   DtCATCH_AND_WARN(std::cout);
   return 0;
}