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Migrating to UNIGINE from Unreal Engine: Programming

Game logic in an Unreal Engine project is implemented via Blueprint Script / C++ components. You got used to determine actor's behavior by writing event functions like InitializeComponent() and TickComponent().

In UNIGINE, you can create projects based on C++, C#, and UnigineScript API. A visual scripting feature is being under research and development at the moment.

The traditional workflow implies the Application Logic has three basic components that have different lifetimes:

  • SystemLogic (the AppSystemLogic.cpp source file) exists during the application life cycle.
  • WorldLogic (the AppWorldLogic.cpp source file) takes effect only when a world is loaded.
  • EditorLogic (the AppEditorLogic.cpp source file) takes effect only when a custom editor is loaded (there is a class derived from the EditorLogic class).

Check out the Programming Quick Start series to get started in traditional C++ programming in UNIGINE.

Regarding components, UNIGINE has quite a similar concept, which can be easily adopted — C++ Component System, which is safe and secure and ensures high performance. Logic is written in C++ classes derived from the ComponentBase class, based on which the engine generates a set of component's parameters — Property that can be assigned to any node in the scene. Each component has a set of functions (init(), update(), etc.), that are called by the corresponding functions of the engine's main loop.

From here on, this article covers primarily programming in C++ using the C++ Component System as a more natural and familiar workflow for Unreal Engine users. Check out the Using C++ Component System article for an example for beginners.

Programming in UNIGINE using C++ is not much different from programming in Unreal Engine except that you need to make some preparations and create headers files for components as in the natural coding in C++. For example, let's compare how simple components are created in both engines. In UE4:

Source code (C++)
class UMyComponent : public UActorComponent

    // Called after the owning Actor was created
    void InitializeComponent();

    // Called when the component or the owning Actor is being destroyed
    void UninitializeComponent();

    // Component version of Tick
    void TickComponent(float DeltaTime, enum ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction);

And in UNIGINE. To make the things work, you need to initialize the Component System in the AppSystemLogic.cpp file:

Source code (C++)
/* .. */
#include <UnigineComponentSystem.h>

/* .. */

int AppSystemLogic::init()
	// Write here code to be called on engine initialization.

	return 1;

And then you can write a new component.


Source code (C++)
#pragma once
#include <Unigine.h>
#include <UnigineComponentSystem.h>

using namespace Unigine;
class MyComponent : public ComponentBase
	// declare the component
	COMPONENT(MyComponent, ComponentBase);

	// declare methods to be called at the corresponding stages of the execution sequence

	// declare the name of the property to be used in the Editor

	void init();
	void update();
	void shutdown();



Source code (C++)
#include "MyComponent.h"

// register the component in the Component System

// called on component initialization
void MyComponent::init(){}

// called every frame
void MyComponent::update(){}

// called on component or the owning node is being destroyed
void MyComponent::shutdown(){}

After that, you need to perform the following steps:

  1. Build the application using the IDE.
  2. Run the application once to get the component property generated by the engine.
  3. Assign the property to a node.
  4. Finally, you can check out its work by launching the application.

To learn more about the execution sequence and how to build components, follow the links below:

For those who prefer C#, UNIGINE allows creating C# applications using C# API and, if required, C# Component System.

Writing Gameplay Code#

Printing to Console#

Unreal Engine UNIGINE
Source code (C++)
UE_LOG(LogTemp, Warning, TEXT("Your message"));
Source code (C++)
Log::message("Debug info: %s\n", text);
Log::message("Debug info: %d\n", number);

See Also#

  • More types of messages in the Log class API
  • Video tutorial demonstrating how to print user messages to console using C# Component System

Loading a Scene#

Unreal Engine UNIGINE
Source code (C++)
UGameplayStatics::OpenLevel(GetWorld(), TEXT("MyLevelName"));
Source code (C++)

Accessing Actor/Node from Component#

Unreal Engine UNIGINE
Source code (C++)
Source code (C++)
NodePtr owning_node = node;

See Also#

  • Video tutorial demonstrating how to access nodes from components using C# Component System.

Accessing a Component from the Actor/Node#

Unreal Engine:

Source code (C++)
UMyComponent* MyComp = MyActor->FindComponentByClass<UMyComponent>();


Source code (C++)
MyComponent* my_component = getComponent<MyComponent>(node);

Finding Actors/Nodes#

Unreal Engine:

Source code (C++)
// Find Actor by name (also works on UObjects)
AActor* MyActor = FindObject<AActor>(nullptr, TEXT("MyNamedActor"));

// Find Actors by type (needs a UWorld object)
for (TActorIterator<AMyActor> It(GetWorld()); It; ++It)
	AMyActor* MyActor = *It;
	// ...


Source code (C++)
// Find a Node by name
NodePtr my_node = World::getNodeByName("my_node");

// Find all nodes having this name
Vector<NodePtr> nodes;
World::getNodesByName("test", nodes);

// Find the index of a direct child node
int index = node->findChild("child_node");
NodePtr direct_child = node->getChild(index);

// Perform a recursive descend down the hierarchy to find a child Node by name
NodePtr child = node->findNode("child_node", 1);

Casting From Type to Type#

Downcasting (from a pointer-to-base to a pointer-to-derived) is performed using different constructions. To perform Upcasting (from a pointer-to-derived to a pointer-to-base) you can simply use the instance itself.

Unreal Engine:

Source code (C++)
UPrimitiveComponent* Primitive = MyActor->GetComponentByClass(UPrimitiveComponent::StaticClass());
USphereComponent* SphereCollider = Cast<USphereComponent>(Primitive);
if (SphereCollider != nullptr)
// ...


Source code (C++)
// find a pointer to node by a given name
NodePtr baseptr = World::getNodeByName("my_meshdynamic");

// cast a pointer-to-derived from pointer-to-base with automatic type checking
ObjectMeshDynamicPtr derivedptr = checked_ptr_cast<ObjectMeshDynamic>(baseptr);

// static cast (pointer-to-derived from pointer-to-base)
ObjectMeshDynamicPtr derivedptr = static_ptr_cast<ObjectMeshDynamic>(World::getNodeByName("my_meshdynamic"));

// upcast to the pointer to the Object class which is a base class for ObjectMeshDynamic
ObjectPtr object = derivedptr;

// upcast to the pointer to the Node class which is a base class for all scene objects
NodePtr node = derivedptr;

Destroy Actor/Node#

Unreal Engine UNIGINE
Source code (C++)

// destroy the actor with 1 second delay
Source code (C++)
node.deleteLater(); // recommended option
//called between the current and the next frames

node.deleteForce(); // called during the same frame but unsafe

To perform deferred removal of a node in UNIGINE, you can create a component that will be responsible for the timer and deletion.

Instantiating Actor / Node Reference#

In UE4, you create a clone of an actor the following way:

Source code (C++)
AMyActor* CreateCloneOfMyActor(AMyActor* ExistingActor, FVector SpawnLocation, FRotator SpawnRotation)
UWorld* World = ExistingActor->GetWorld();
FActorSpawnParameters SpawnParams;
SpawnParams.Template = ExistingActor;
World->SpawnActor<AMyActor>(ExistingActor->GetClass(), SpawnLocation, SpawnRotation, SpawnParams);

In UNIGINE, you should use World::loadNode to load a hierarchy of nodes from a .node asset. In this case the hierarchy of nodes that was saved as a NodeReference will be added to the scene. You can refer to the asset either via a component parameter or manually by providing the virtual path to it:

Source code (C++)
// MyComponent.h
PROP_PARAM(File, node_to_spawn);
Source code (C++)
// MyComponent.cpp
/* .. */

void MyComponent::init() 

	// load a hierarchy of nodes from the asset
	NodePtr spawned = World::loadNode(node_to_spawn.get());

	NodePtr spawned_manually = World::loadNode("nodes/node_reference.node");

In case of using the approach of component parameters, you should also specify the .node asset:

You can also spawn the NodeReference as a single node (without extracting the content) in the world:

Source code (C++)
void MyComponent::update() 

	NodeReferencePtr nodeRef = NodeReference::create("nodes/node_reference_0.node");


Unreal Engine:

Source code (C++)
class AMyActor : public AActor

// My trigger component
UPrimitiveComponent* Trigger;

	Trigger = CreateDefaultSubobject<USphereComponent>(TEXT("TriggerCollider"));

	// Both colliders need to have this set to true for events to fire
	Trigger.bGenerateOverlapEvents = true;

	// Set the collision mode for the collider
	// This mode will only enable the collider for raycasts, sweeps, and overlaps

virtual void NotifyActorBeginOverlap(AActor* Other) override;

virtual void NotifyActorEndOverlap(AActor* Other) override;

In UNIGINE, Trigger is a special built-in node type that raises events in certain situations:

WorldTrigger is the most common type that can be used in gameplay. Here is an example on how to use it:

Source code (C++)
WorldTriggerPtr trigger;
void* enter_callback_id;

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

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

int AppWorldLogic::init()

	node = NodeDummy::create();
	node2 = NodeDummy::create();

	// 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;


UE4 Input:

Source code (C++)
class AMyPlayerController : public APlayerController

    void SetupInputComponent()

        InputComponent->BindAction("Fire", IE_Pressed, this, &AMyPlayerController::HandleFireInputEvent);
        InputComponent->BindAxis("Horizontal", this, &AMyPlayerController::HandleHorizontalAxisInputEvent);
        InputComponent->BindAxis("Vertical", this, &AMyPlayerController::HandleVerticalAxisInputEvent);

    void HandleFireInputEvent();
    void HandleHorizontalAxisInputEvent(float Value);
    void HandleVerticalAxisInputEvent(float Value);


Source code (C++)
void MyInputController::update()

	// if right mouse button is clicked
	if (Input::isMouseButtonDown(Input::MOUSE_BUTTON_RIGHT))
		Math::ivec2 mouse = Input::getMousePosition();
		// report mouse cursor coordinates to the console
		Log::message("Right mouse button was clicked at (%d, %d)\n", mouse.x, mouse.y);

	// closing the application if a 'Q' key is pressed, ignoring the key if the console is opened
	if (Input::isKeyDown(Input::KEY_Q) && !Console::isActive())

You can also use the ControlsApp class to handle control bindings. To configure the bindings, open the Controls settings:

Source code (C++)
void MyInputController::init()

	// remapping states to other keys and buttons
	ControlsApp::setStateKey(Controls::STATE_FORWARD, Input::KEY_PGUP);
	ControlsApp::setStateKey(Controls::STATE_BACKWARD, Input::KEY_PGDOWN);
	ControlsApp::setStateKey(Controls::STATE_MOVE_LEFT, Input::KEY_L);
	ControlsApp::setStateKey(Controls::STATE_MOVE_RIGHT, Input::KEY_R);
	ControlsApp::setStateMouseButton(Controls::STATE_JUMP, Input::MOUSE_BUTTON_LEFT);

void MyInputController::update()

	if (ControlsApp::clearState(Controls::STATE_FORWARD))
		Log::message("FORWARD key pressed\n");
	else if (ControlsApp::clearState(Controls::STATE_BACKWARD))
		Log::message("BACKWARD key pressed\n");
	else if (ControlsApp::clearState(Controls::STATE_MOVE_LEFT))
		Log::message("MOVE_LEFT key pressed\n");
	else if (ControlsApp::clearState(Controls::STATE_MOVE_RIGHT))
		Log::message("MOVE_RIGHT key pressed\n");
	else if (ControlsApp::clearState(Controls::STATE_JUMP))
		Log::message("JUMP button pressed\n");

/* .. */

Ray Tracing#

Unreal Engine:

Source code (C++)
APawn* AMyPlayerController::FindPawnCameraIsLookingAt()
// You can use this to customize various properties about the trace
FCollisionQueryParams Params;
// Ignore the player's pawn

// The hit result gets populated by the line trace
FHitResult Hit;

// Raycast out from the camera, only collide with pawns (they are on the ECC_Pawn collision channel)
FVector Start = PlayerCameraManager->GetCameraLocation();
FVector End = Start + (PlayerCameraManager->GetCameraRotation().Vector() * 1000.0f);
bool bHit = GetWorld()->LineTraceSingle(Hit, Start, End, ECC_Pawn, Params);

if (bHit)
	// Hit.Actor contains a weak pointer to the Actor that the trace hit
	return Cast<APawn>(Hit.Actor.Get());

return nullptr;

In UNIGINE the same is handled by Intersections:

Source code (C++)
#include "MyComponent.h"
#include <UnigineWorld.h>
#include <UnigineVisualizer.h>
#include <UnigineGame.h>
#include <UnigineInput.h>

using namespace Unigine;
using namespace Math;


void MyComponent::init() 


void MyComponent::update() 

	ivec2 mouse = Input::getMousePosition();
	float length = 100.0f;
	Vec3 start = Game::getPlayer()->getWorldPosition();
	Vec3 end = start + Vec3(Game::getPlayer()->getDirectionFromMainWindow(mouse.x, mouse.y)) * length;

	// ignore surfaces that have certain bits of the Intersection mask enabled
	int mask = ~(1 << 2 | 1 << 4);

	WorldIntersectionNormalPtr intersection = WorldIntersectionNormal::create();

	ObjectPtr obj = World::getIntersection(start, end, mask, intersection);

	if (obj)
		Vec3 point = intersection->getPoint();
		vec3 normal = intersection->getNormal();
		Visualizer::renderVector(point, point + Vec3(normal), vec4_one);
		Log::message("Hit %s at (%f,%f,%f)\n", obj->getName(), point.x, point.y, point.z);
Last update: 2022-12-14
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