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Callbacks

Any function from system, world or editor scripts can be called in a C++ code. UnigineScript functions that are called from an external code are known as callbacks. Via callbacks scripts can communicate with each other, as well as with the external application.

  • Callbacks support up to 4 arguments and can return a value of an arbitrary type.

See also

An example can be found in <UnigineSDK>/source/samples/Api/Scripts/Callbacks/ directory.

Callbacks Usage Example

C++ Side

To demonstrate how callbacks can be used, let's code the C++ part first:

Source code (C++)
#include <UnigineEngine.h>
#include <UnigineInterpreter.h>

using namespace Unigine;

/******************************************************************************\
*
* World function
*
\******************************************************************************/

/*
*/
const Variable &runWorldFunction(const Variable &name,const Variable &v) {
	
	Log::warning("runWorldFunction(%s,%s) is called\n",name.getTypeName().get(),v.getTypeName().get());
	
	Engine *engine = Engine::get();
	return engine->runWorldFunction(name,v);
}

/******************************************************************************\
*
* Main
*
\******************************************************************************/

/*
*/
int main(int argc,char **argv) {
	
	// export the runWorldFunction() function defined above
	Interpreter::addExternFunction("runWorldFunction",MakeExternFunction(&runWorldFunction));
	
	// initialize the engine
	Engine *engine = Engine::init(UNIGINE_VERSION,argc,argv);
	
	// start the main loop
	while(engine->isDone() == 0) {
		
		engine->update();
		engine->render();
		engine->swap();
		
		// call the counter() function of the script (defined below)
		Variable ret = engine->runWorldFunction(Variable("counter"));
		// print a message depending on the value returned by the counter() script function:
		// print the current value of the counter
		if(ret.getInt() != -1) Log::message("counter is: %d\n",ret.getInt());
		// print the world name
		if(ret.getInt() == 3) Log::message("\nworld name is: \"%s\"\n",engine->runWorldFunction(Variable("engine.world.getName")).getString());
	}
	
	// shut down the engine and call the shutdown() function in the loaded world script
	Engine::shutdown();
	
	return 0;
}

Unigine Script Side

And now the UnigineScript side where callbacks are defined:

Source code (UnigineScript)
// my_world.cpp

/*
*/
int callback(int value) {
	
	log.warning("callback(%s) is called\n",typeinfo(value));
	
	return value;
}

/*
*/
void counter() {
	
	for(int i = 0; i < 4; i++) {
		log.warning("counter(): called\n");
		yield i;
	}
	
	return -1;
}

/*
*/
int init() {
	
	log.message("\n");
	
	// run the callback() script function via the API runWorldFunction() function
	log.message("result is: %s\n\n",typeinfo(runWorldFunction("callback",10)));
	log.message("result is: %s\n\n",typeinfo(runWorldFunction("callback",vec3(1,2,3))));
	log.message("result is: %s\n\n",typeinfo(runWorldFunction("callback","a string")));
	
	/////////////////////////////////
	
	// show a console
	engine.console.setActivity(1);
	
	return 1;
}

Calling Sequence

The sequence of function call will be as follows:

  1. The interpreter exports the runWorldFunction() function to make it available from the script.
  2. The engine is initialized, and the init() function of the script is called. This function calls the exported runWorldFunction() function.
  3. The exported runWorldFunction() function calls the callback() function from the script.
  4. The engine enters the main loop, where it calls the counter() function from the script by using the Unigine::Engine::runWorldFunction() function.

Output

The following result will be printed into the console:

Output
runWorldFunction(string,int): called
callback(int: 10): called
result is: int: 10

runWorldFunction(string,vec3): called
callback(vec3: 1 2 3): called
result is: vec3: 1 2 3

runWorldFunction(string,string): called
callback(string: "a string") is called
result is: string: "a string"

counter(): called
counter is: 0
counter(): called
counter is: 1
counter(): called
counter is: 2
counter(): called
counter is: 3

world name is: "data/callbacks"
Last update: 2017-07-03