Say for instance I wanted to add a callback within a function. In HPL Engine there's quite of them called: AddTimer(const string& asName, float time, const string& asFunction); Usage would be given:

void onEnter() {
    AddTimer("Timer1",2.0, "Funct1");
}
void Funct1(string &asFunction) {
//... Do something ..//
}

I don't know why but I got a feeling inside AddTimer C++ function they create a new module and build it upon initialization. The declared function being whatever the third parameter be inside AddTimer. Upon rendering time - they would execute all the modules functions?

Most likely they are doing something like this:

// C++ implementation
void AddTimer(const string &asName, float time, const string &asFunction)
{
   // Find the function that should be called
   asIScriptModule *mod = engine->GetModule("game", asGM_ONLY_IF_EXISTS);
   asIScriptFunction *func = mod->GetFunctionByName(asFunction.c_str());
 
   // Store the function and argument for when it is time to call it
   ...
}
 
void CallTimerCallback()
{
   // Retrieve the function to call and argument from the storage
   ...
 
   // Prepare a context and call the function
   asIScriptContext *ctx = engine->RequestContext();
   ctx->Prepare(func);
   ctx->SetArgObject(0, asName);
   ctx->Execute();
   
   engine->ReturnContext(ctx);
}

You can get more information on how to use callbacks from the manual.

Most likely they are doing something like this:

// C++ implementation
void AddTimer(const string &asName, float time, const string &asFunction)
{
   // Find the function that should be called
   asIScriptModule *mod = engine->GetModule("game", asGM_ONLY_IF_EXISTS);
   asIScriptFunction *func = mod->GetFunctionByName(asFunction.c_str());
 
   // Store the function and argument for when it is time to call it
   ...
}
 
void CallTimerCallback()
{
   // Retrieve the function to call and argument from the storage
   ...
 
   // Prepare a context and call the function
   asIScriptContext *ctx = engine->RequestContext();
   ctx->Prepare(func);
   ctx->SetArgObject(0, asName);
   ctx->Execute();
   
   engine->ReturnContext(ctx);
}

You can get more information on how to use callbacks from the manual.

Thanks Andreas - I just figured it has to be like that almost. I viewed the HPL 1 engine source code and it was entangled into a lot of things but the summary was that it was just like you mentioned. There was a callback linking back to the scripting interface. It was pretty confusing to follow though how they achieved it.