Event Handling Callbacks

void ThisClass::callback_function(NodePtr, int) {
	/* .. */
}
// create a callback with no predefined parameters
CallbackBase2<NodePtr, int> *callback = MakeCallback(this, &ThisClass::callback_function);

// create a callback with predefined parameters
CallbackBase2<NodePtr, int> *callback2 = MakeCallback(this, &ThisClass::callback_function, NodeDummy::create()->getNode(), 1);

// create a callback with parameters from lambda
CallbackBase2<NodePtr, int> *callback = MakeCallback([](NodePtr node, int value) { /* .. */ });

// create a callback with parameters from generic lambda
CallbackBase2<NodePtr, int> *callback = MakeCallback([](auto node, auto value) { /* .. */ });

To use overloaded functions and methods as callbacks, provide the template parameters:
MakeCallback< Class, ReturnType, Callback Parameters Types >

Source code (C++)

void ThisClass::callback_method()
{
	/* .. */
}

void ThisClass::callback_method(WidgetPtr w, WidgetPtr w2, int i)
{
	/* .. */
}

CallbackBase *callback = MakeCallback<ThisClass, void, WidgetPtr, WidgetPtr, int>(this, &ThisClass::callback_method);

To raise a custom callback, the run() function of one of the CallbackBase classes is used.

Source code (C++)

// run the callback with no parameters or with default predefined parameters
callback->run();

// run the callback with the specified parameters
callback->run(node, 2);

You can also use lambda expressions for callbacks:

Source code (C++)

// create a callback from lambda
int value = 5;
CallbackBase* callback = MakeCallback([value](){ /* .. */ });

// or std function
std::function<void()> callable_obj = [value]() { /* .. */ };
CallbackBase* callback = MakeCallback(callable_obj);

// or any other type of callable
struct Callable
{
void operator()() const { /* .. */ }
int value;
} callable_obj = { /* .. */ };

CallbackBase* callback = MakeCallback(callable_obj);

Usage Example#

The following section contains the complete source code of a simple callback usage example.

AppWorldLogic.h

#ifndef __APP_WORLD_LOGIC_H__
#define __APP_WORLD_LOGIC_H__

#include <UnigineLogic.h>
#include <UnigineStreams.h>
#include <UnigineCallback.h>

using namespace Unigine;
using namespace Math;

class AppWorldLogic: public Unigine::WorldLogic
{

public:

	int init() override;

	int update() override;
	int postUpdate() override;
	int updatePhysics() override;

	int shutdown() override;

	int save(const Unigine::StreamPtr &stream) override;
	int restore(const Unigine::StreamPtr &stream) override;
};

#endif // __APP_WORLD_LOGIC_H__

AppWorldLogic.cpp

#include "AppWorldLogic.h"

class SomeClass
{
public:
	// a member function to be called on the action
	void callback_method(int a, int b)
	{
		Log::message("\tcallback_method has been called %d %d\n", a, b);
	}

	void create_callbacks()
	{
		Log::message("Create a callback with no predefined parameters\n");
		CallbackBase * callback = MakeCallback(this, &SomeClass::callback_method);

		// run the callback with two parameters
		callback->run(73, 37);
		// run the callback with no parameters.
		// if the callback function has arguments, this will lead to unsafe behaviour
		callback->run();

		Log::message("Create a callback with predefined parameters\n");
		CallbackBase * callback2 = MakeCallback(this, &SomeClass::callback_method, 1, 2);

		// run the callback with no parameters. In this case, the predefined parameters will be used
		callback2->run();
		// run the callback with parameters. The predefined ones will be ignored
		callback2->run(351, 153);
		// run the callback with only 1 parameter.
		// the second predefined parameter will be used as the second argument
		callback2->run(118);
	}
};

// a callback function to be called on the action
void callback_function(int a, int b)
{
	Log::message("\tcallback_function has been called %d %d\n", a, b);
}

int AppWorldLogic::init()
{
	SomeClass *some = new SomeClass();
	// call the SomeClass member function
	some->create_callbacks();

	Log::message("Create a callback in the other instance\n");
	// use the callback function of the SomeClass to create a callback
	CallbackBase * callback3 = MakeCallback(some, &SomeClass::callback_method, 5, 25);
	callback3->run();

	Log::message("Create callback functions\n");
	CallbackBase * callback4 = MakeCallback(&callback_function);
	callback4->run(20, 70);
	CallbackBase * callback5 = MakeCallback(&callback_function, 50, 25);
	callback5->run();

	return 1;
}

int AppWorldLogic::update()
{

	return 1;
}

int AppWorldLogic::postUpdate()
{
	return 1;
}

int AppWorldLogic::updatePhysics()
{
	return 1;
}

int AppWorldLogic::shutdown()
{
	return 1;
}

int AppWorldLogic::save(const Unigine::StreamPtr &stream)
{
	UNIGINE_UNUSED(stream);
	return 1;
}

int AppWorldLogic::restore(const Unigine::StreamPtr &stream)
{
	UNIGINE_UNUSED(stream);
	return 1;
}

Practical Use#

Callbacks are widely used in event handling. A number of Unigine API members have several predefined events which can be handled by using callbacks in certain cases.

Triggers#

Triggers are used to detect changes in nodes position or state. Unigine offers three types of built-in triggers:

NodeTrigger fires callbacks when the trigger node is enabled or the trigger node position has changed.
WorldTrigger fires callbacks when any node (collider or not) gets inside or outside of it.
PhysicalTrigger fires callbacks when physical objects get inside or outside of it.

Here is a simple WorldTrigger usage example:

Source code (C++)

WorldTriggerPtr trigger;
void *enter_callback_id;

// implement the enter callback
void AppWorldLogic::enter_callback(NodePtr node)
{
	Log::message("\nA node named %s has entered the trigger\n", node->getName());
}

// implement the leave callback
void AppWorldLogic::leave_callback(NodePtr node)
{
	Log::message("\nA node named %s has left the trigger\n", node->getName());
}

int AppWorldLogic::init()
{

	// create a world trigger node
	trigger = WorldTrigger::create(Math::vec3(3.0f));

	// add the enter callback to be fired when a node enters the world trigger
	// and keep its id to be used to remove the callback when necessary
	enter_callback_id = trigger->addEnterCallback(MakeCallback(this, &AppWorldLogic::enter_callback));
	// add the leave callback to be fired when a node leaves the world trigger
	trigger->addLeaveCallback(MakeCallback(this, &AppWorldLogic::leave_callback));

	return 1;
}

To remove the callbacks use the following code:

Source code (C++)

// remove the callback by using its id
trigger->removeEnterCallback(enter_callback_id);
// clear all leave callbacks
trigger->clearLeaveCallbacks();

Widgets#

The widgets base class Widget allows registering callbacks for events defined in the GUI class. The following example shows how to create a WidgetButton and register a callback function for the CLICKED event:

Source code (C++)

// event handler function
int AppWorldLogic::onButtonClicked()
{
	Log::message("\nThe widget button has been clicked\n");

	return 1;
}

int AppWorldLogic::init()
{

	// get a pointer to the system GUI
	GuiPtr gui = Gui::getCurrent();
	// create a button widget and set its caption
	WidgetButtonPtr widget_button = WidgetButton::create(gui, "Press me");
	// set a tooltip
	widget_button->setToolTip("Click this button");
	// rearrange a button size
	widget_button->arrange();
	// set a button position
	widget_button->setPosition(10, 10);
	// set the onButtonClicked function to handle the CLICKED event
	widget_button->addCallback(Gui::CLICKED, MakeCallback(this, &AppWorldLogic::onButtonClicked));
	// add the created button widget to the system GUI
	gui->addChild(widget_button, Gui::ALIGN_OVERLAP | Gui::ALIGN_FIXED);

	return 1;
}

Physics#

You can track certain events of the physics-related Bodies and Joints:

Body::addFrozenCallback() to track an event when a body freezes.
Body::addPositionCallback() to track an event when a body changes its position.
Body::addContactEnterCallback() to track an event when a contact emerges (body starts touching another body or collidable surface).
Body::addContactLeaveCallback() to track an event when a contact ends (body stops touching another body or collidable surface).
Body::addContactsCallback() to get all contacts of the body including new ones (enter) and the ending ones (leave). Leave contacts are removed after the callback execution stage, so this is the only point where you can still get them.
Joint::addBrokenCallback() to track an event when a joint breaks.

The following sample shows the way of registering callbacks for a BodyRigid and change the color of a mesh depending on its state:

Source code (C++)

// set the node's albedo color to red on the freezing event
int AppWorldLogic::frozen_callback(BodyPtr body)
{
	body->getObject()->setMaterialParameterFloat4("albedo_color", vec4(1.0f, 0.0f, 0.0f, 1.0f), 0);

	return 1;
}

// set the node's albedo color to blue on the position change event
int AppWorldLogic::position_callback(BodyPtr body)
{
	body->getObject()->setMaterialParameterFloat4("albedo_color", vec4(0.0f, 0.0f, 1.0f, 1.0f), 0);

	return 1;
}

// set the node's albedo color to yellow on each contact
int AppWorldLogic::contact_enter_callback(BodyPtr body, int num)
{
	body->getObject()->setMaterialParameterFloat4("albedo_color", vec4(1.0f, 1.0f, 0.0f, 1.0f), 0);

	return 1;
}

int AppWorldLogic::init()
{

	// create a box
	ObjectMeshStaticPtr meshStatic = ObjectMeshStatic::create("core/meshes/box.mesh");
	meshStatic->setPosition(Vec3(0, 0, 5.0f));
	// add a rigid body to the box
	BodyRigidPtr body = BodyRigid::create(meshStatic);
	// register callbacks for events
	body->addFrozenCallback(MakeCallback(this, &AppWorldLogic::frozen_callback));
	body->addPositionCallback(MakeCallback(this, &AppWorldLogic::position_callback));
	body->addContactEnterCallback(MakeCallback(this, &AppWorldLogic::contact_enter_callback));
	// add a shape to the body
	ShapeBoxPtr shape = ShapeBox::create(body, vec3(1.0f));

	return 1;
}

NoticePhysics-based callbacks are executed in the main tread, as they are mainly used for creation, destruction or modification of other objects.

Properties#

Callback functions can be used to determine actions to be performed when adding or removing node and surface properties as well as when swapping node properties. Here is an example demonstrating how to track adding a node property via callbacks:

Source code (C++)

void AppWorldLogic::node_property_added(NodePtr node, PropertyPtr property)
{
	Log::message("Property \"%s\" was added to the node named \"%s\".\n", property->getName(), node->getName());
}

int AppWorldLogic::init()
{

	NodeDummyPtr node = NodeDummy::create();

	// search for a property named "new_property_0"
	PropertyPtr property = Properties::findProperty("new_property_0");

	// set the callback function on adding a node property
	node->addCallback(Node::CALLBACK_PROPERTY_NODE_ADD, MakeCallback(this, &AppWorldLogic::node_property_added));

	// add the property named "new_property_0" to the node
	node->addProperty("new_property_0");

	return 1;
}

You can add callbacks to track any changes made to a property and its parameters and perform certain actions.

The example below shows how to add a callback to track changes of property parameters and report the name of the property and the changed parameter.

Source code (C++)

void AppWorldLogic::parameter_changed(PropertyPtr property, int num)
{
	Log::message("Parameter \"%s\" of the property \"%s\" has changed its value.\n", property->getParameterPtr(num)->getName(), property->getName());	
}

int AppWorldLogic::init()
{

	// set the callback function on parameter change
	property->addCallback(Property::CALLBACK_PARAMETER_CHANGED, MakeCallback(this, &AppWorldLogic::parameter_changed));

	// change the value of the "my_int_param" parameter
	property->getParameterPtr("my_int_param")->setValueInt(3);

	return 1;
}

You can also add callbacks to the Properties manager to track any changes made to any property and perform certain actions:

Source code (C++)

void AppWorldLogic::property_removed(PropertyPtr property)
{
	Log::message("Property \"%s\" was removed.\n", property->getName());
}

int AppWorldLogic::init()
{

	// inherit a new property named "new_property_1" from the base property "surface_base"
	Properties::findManualProperty("surface_base")->inherit("new_property_1");

	// set the callback function on property removal
	Properties::addCallback(Properties::CALLBACK_REMOVED, MakeCallback(this, &AppWorldLogic::property_removed));

	// remove the property named "new_property_1"
	Properties::removeProperty(Properties::findProperty("new_property_1")->getGUID());

	return 1;
}

Event Handling Callbacks

In This Article:

Usage Example#

Practical Use#

Triggers#

See Also

Widgets#

See Also

Physics#

See Also

Properties#

See Also#