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Constant Export

Constants are variables, the value of which does not change no matter what happens in C++ code. To be available in Unigine scripts, they need to be exported on C++ side.

  • External constants are read-only.
  • If a value of a registered constant is changed in the C++ code, on script side it will remain the same (unlike variables).

Constant Export Example#

Constants are exported in the similar way as variables:

  1. Create a pointer to an external constant via MakeExternConstant() .
  2. Register the constant via Unigine::Interpreter::addExternVariable() .
  3. All variables are exported into a global namespace. To limit the scope of variable, use library namespace.
Source code (C++)
#include <UnigineEngine.h>
#include <UnigineInterpreter.h>

using namespace Unigine;

int main(int argc,char **argv) {

	int i = 0;
	float f = 0.0f;

	// export a variable and specify a name to access it from Unigine scripts
	Interpreter::addExternVariable("int_constant",MakeExternConstant(i));
	// you can also specify a template parameter to make sure the proper type is passed
	Interpreter::addExternVariable("float_constant",MakeExternConstant<float>(f));
	
	Engine *engine = Engine::init(UNIGINE_VERSION,argc,argv);
	// enter the main loop
	while(engine->isDone() == 0) {
		engine->update();
		engine->render();
		engine->swap();		
		// if a variable value is changed after it was registered, the value in scripts will not be changed
		i = 42;
		f = 57.55f;
	}
	// engine shutdown 
	Engine::shutdown();

}

Access from Scripts#

After the registration, you can access constants from a script by their registered names:

Source code (UnigineScript)
// my_world.usc

log.message("Integer: %d\nFloat: %f\n",int_constant,float_constant);

Output#

The following results will be printed into the console:

Output
Integer: 0
Float: 0.000000

Notice
If you reload the world, the values of the constants that have been changed on the C++ side will remain the same.
Last update: 2019-04-30