Augmented Reality Shopping App Unreal Engine, C++

Okay, let's outline the structure for a simplified Augmented Reality (AR) shopping app example using Unreal Engine and C++. This will focus on the core mechanics:

1.  **Project Setup:** Setting up Unreal Engine for AR.
2.  **AR Session:**  Initializing an AR session to track the environment.
3.  **Object Placement:**  Allowing the user to place a virtual product (a simple cube) in the real world.
4.  **Interaction:**  Enabling basic interaction with the placed object (e.g., rotation).

Here's the code, broken down with explanations:

**1. Project Setup (Unreal Engine):**

*   Create a new Unreal Engine project using the "AR Template" (this includes the necessary AR plugins and components).
*   Alternatively, if using a blank project, enable the "ARSession" and "AugmentedReality" plugins in Edit > Plugins.

**2. C++ Class (MyARObject.h):**

Create a new C++ class derived from `AActor`. Name it `MyARObject`.

```cpp
// MyARObject.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "MyARObject.generated.h"

UCLASS()
class MYPROJECT_API AMyARObject : public AActor
{
	GENERATED_BODY()

public:
	// Sets default values for this actor's properties
	AMyARObject();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:
	// Called every frame
	virtual void Tick(float DeltaTime) override;

	// Root Component (Static Mesh)
	UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "AR", meta = (AllowPrivateAccess = "true"))
	UStaticMeshComponent* MeshComponent;

	// Rotation Speed
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "AR", meta = (AllowPrivateAccess = "true"))
	float RotationSpeed;

	// Function to Rotate the object
	UFUNCTION(BlueprintCallable, Category = "AR")
	void RotateObject(float Value);
};
```

**Explanation:**

*   `#pragma once`:  Header guard to prevent multiple inclusions.
*   `#include`: Includes necessary Unreal Engine headers.
*   `UCLASS()`:  Marks this class as a UObject, enabling Unreal Engine features.
*   `MYPROJECT_API`:  Your project's API macro (replace `MYPROJECT` with your project name) for export/import declarations.
*   `AActor`:  Base class for all actors (objects that can be placed in the world).
*   `GENERATED_BODY()`:  Required macro for UObject classes.
*   `MeshComponent`:  A `UStaticMeshComponent` will hold the visual representation of the AR object (e.g., a cube).  `VisibleAnywhere` means you can see this component in the editor. `BlueprintReadOnly` means blueprints can read but not modify its properties.  `Category = "AR"` organizes the property in the details panel. `meta=(AllowPrivateAccess="true")` allows the private access from blueprints.
*   `RotationSpeed`: A variable that allows to control rotation speed in the editor.
*   `RotateObject`:  This function is called for rotation. `BlueprintCallable` so that you can call the function inside blueprint.

**3. C++ Class (MyARObject.cpp):**

```cpp
// MyARObject.cpp

#include "MyARObject.h"
#include "Components/StaticMeshComponent.h"

// Sets default values
AMyARObject::AMyARObject()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	// Create a static mesh component
	MeshComponent = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("MeshComponent"));
	RootComponent = MeshComponent;

	// Default Rotation Speed
	RotationSpeed = 50.0f; // Degrees per second
}

// Called when the game starts or when spawned
void AMyARObject::BeginPlay()
{
	Super::BeginPlay();

}

// Called every frame
void AMyARObject::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

	// No tick logic currently
}

void AMyARObject::RotateObject(float Value)
{
	FRotator NewRotation = FRotator(0.0f, Value * RotationSpeed * GetWorld()->GetDeltaSeconds(), 0.0f);
	AddActorLocalRotation(NewRotation);
}
```

**Explanation:**

*   `#include`: Includes necessary headers.
*   `AMyARObject::AMyARObject()`:  Constructor.  Initializes the `MeshComponent`.
    *   `PrimaryActorTick.bCanEverTick = true;`: Allows the `Tick` function to be called every frame.
    *   `CreateDefaultSubobject`: Creates an instance of `UStaticMeshComponent` and assigns it to `MeshComponent`.
    *   `RootComponent = MeshComponent`: Sets the static mesh as the root component.  This is important for positioning and transforms.
*   `BeginPlay()`: Called when the actor is spawned in the world.  Empty in this example.
*   `Tick()`: Called every frame. Empty in this example. You can add additional logic, such as animation.
*   `RotateObject()`:  Rotates the object based on input value and RotationSpeed.
    *   `FRotator NewRotation`: Creates a new rotator, value is multiplied by RotationSpeed and DeltaSeconds to make the rotation framerate-independent.
    *   `AddActorLocalRotation()`: Applies the rotation to the object.
**4. Blueprint Setup (for AR Placement):**

*   Open your level Blueprint.
*   Find a way to trigger the spawning of your AR object.  This can be a touch event, a button press, or other input.  Let's assume a simple touch event.

```cpp
//Inside Event Touch Event
{
    FHitResult HitResult;
    bool bHit = GetWorld()->GetFirstPlayerController()->GetHitResultUnderFinger(ETouchIndex::Touch1, ECC_Visibility, HitResult);

    if (bHit)
    {
        // Spawn the AR object at the hit location
        FActorSpawnParameters SpawnParams;
        SpawnParams.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AdjustIfPossibleButAlwaysSpawn;
        AMyARObject* SpawnedObject = GetWorld()->SpawnActor<AMyARObject>(AMyARObject::StaticClass(), HitResult.Location, FRotator::ZeroRotator, SpawnParams);
    }
}
```

**Explanation:**

*   `GetWorld()->GetFirstPlayerController()->GetHitResultUnderFinger()`:  Performs a raycast from the user's touch location in the real world. `ETouchIndex::Touch1` specifies the first touch. `ECC_Visibility` is the collision channel to trace against.
*   `HitResult`: Contains information about the hit, including the `HitResult.Location`.
*   `FActorSpawnParameters`: Allows to specify the spawning parameters.
*   `SpawnParams.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AdjustIfPossibleButAlwaysSpawn;`: If the object overlaps another collision, then the object will be moved slightly to avoid the intersection.
*   `GetWorld()->SpawnActor()`: Spawns an actor of the specified class (`AMyARObject`) at the hit location.
*   `FRotator::ZeroRotator`: Creates a rotator with all angles set to 0.
*   `SpawnedObject`: A pointer to the spawned `AMyARObject`.

**5. Blueprint Setup (for Rotation):**

*   Inside your Level Blueprint, implement a system that allows the user to rotate the object.

```cpp
//Inside Event Tick
{
    float RotationValue = 1.0f; // Example rotation value

    if(SpawnedObject != nullptr)
    {
        SpawnedObject->RotateObject(RotationValue);
    }
}
```

**Explanation:**

*   `RotationValue`:  The value to rotate the object.
*   `SpawnedObject->RotateObject(RotationValue);`: Calls the function to rotate the object.

**Important Considerations:**

*   **AR Session Component:** Make sure you have an `ARSessionComponent` in your level.  This component handles the tracking and management of the AR session.
*   **Collision:** Ensure you have proper collision set up on the `MeshComponent` of your `AMyARObject`. This will allow the raycast to hit and prevent the object from passing through surfaces.  You can set the collision preset in the editor.
*   **Mobile Platform:**  To run this on a mobile device, you'll need to configure your project for your target platform (Android or iOS).  This involves setting up the SDK, building the project, and deploying it to the device.  Refer to Unreal Engine's official documentation for mobile development.
*   **Scaling:** AR objects often appear too large or too small.  Adjust the scale of your `MeshComponent` in the editor to achieve a realistic size relative to the real world.
*   **Error Handling:** Add error handling to gracefully handle cases where the AR session fails to start or tracking is lost.

**How to Use:**

1.  Create an AR template Project.
2.  Create the `MyARObject` C++ class (header and source files).
3.  Compile the C++ code.
4.  Open your level blueprint.
5.  Implement the placement logic (spawn object on touch) using the code provided.
6.  Implement the rotation logic (call the rotation function on tick).
7.  Compile and run the project on a mobile device that supports ARCore (Android) or ARKit (iOS).

This example provides a basic foundation. You can extend it with more features, such as:

*   Loading different product models.
*   Resizing/scaling the product.
*   Adding textures and materials.
*   Using AR anchors for persistent placement.
*   Implementing advanced interactions (e.g., gestures).

Remember to consult the Unreal Engine documentation for more in-depth information on AR development. Good luck!