Unreal Engine Chapter 4: Creating the Map and Point of Interest

In this chapter we will wrap up the data transitioning from JavaScript to Unreal C++. This will be marked by the implementation of the Map model.

Overview of the required Map model data

Looking at the data of the map object from the Chapter 9 model.js of the original Starter Guide, we will require another C++ class to be created from the Editor, called MapModel and once again, to spare us unnecessary code noise, we can set its parent class to be UObject.

Now let’s go over the things we will need:

  • We want to once again include the three binders - CohtmlUTypeBinder.h,CohtmlFStringBinder.h and CohtmlTArrayBinder.h
  • We want to specify our class constructor
  • We want a zoom, x and y variable of type float
  • We want a pointsOfInterest variable, which will be a TArray of PointOfInterest objects
    • PointOfInterest will be a USTRUCT, which requires:
      • A x and y variable of type float
      • An icon, title and description variable of type FString
      • A locked variable of type bool
  • We want a mapTiles variable, which is going to be another TArray, containing MapTile objects
    • This will be a dummy USTRUCT, that will contain no data, but is required since the data-bind-for expression in the index.html depends on its existance the way it is implemented, but essentially does nothing. It is a struct, because the data-bind-for won’t generate the tiles if the array consists of primitive types
    • We will also add a const uint32 variable for the tile size

Once again, all of these member variables will be exposed by using the UPROPERTY macro.

Implementing the Map model

Now that we have a list of the data that we need, we can start going over the actual code. Let’s start with the MapModel.h:

#pragma once

#include <CohtmlUTypeBinder.h>
#include <CohtmlFStringBinder.h>
#include <CohtmlTArrayBinder.h>

#include "MapModel.generated.h"

USTRUCT()
struct FPointOfInterest
{
    GENERATED_BODY()

    FPointOfInterest()
        : x(0.0f)
        , y(0.0f)
        , locked(false)
    {
    }

    FPointOfInterest(float X, float Y, FString Icon, FString Title, FString Description, bool Locked)
        : x(X)
        , y(Y)
        , icon(Icon)
        , title(Title)
        , description(Description)
        , locked(Locked)
    {
    }
    
    UPROPERTY()
    float x;

    UPROPERTY()
    float y;

    UPROPERTY()
    FString icon;

    UPROPERTY()
    FString title;

    UPROPERTY()
    FString description;

    UPROPERTY()
    bool locked;
};

// This struct is needed for the automatic generation of the
// map tiles, through the usage of the data-bind-for expression
// in the index.html.
USTRUCT()
struct FMapTile
{
    GENERATED_BODY()

    int32 id;
};

UCLASS()
class COHERENTSAMPLE_API UMapModel : public UObject
{
    GENERATED_BODY()

public:
    UMapModel();

    UPROPERTY()
    float zoom;

    UPROPERTY()
    float x;

    UPROPERTY()
    float y;

    UPROPERTY()
    TArray<FPointOfInterest> pointsOfInterest;

    UPROPERTY()
    TArray<FMapTile> mapTiles;

private:
    const uint32 MAP_TILES_SIZE = 64;
};

Evidently it is as simple as can be. Same goes for the MapModel.cpp, where we just need to perform the variable initialization and add the 3 “points of interest":

#include "StarterGuide/MapModel.h"

UMapModel::UMapModel()
    : zoom(1.0f)
    , x(0.0f)
    , y(0.0f)
{
    pointsOfInterest.Add(FPointOfInterest(10.3004f, 45.7164f, "village", "Village", "The village where you were raised.", false));
    pointsOfInterest.Add(FPointOfInterest(22.6609f, 14.1493f, "town", "Town", TEXT("The town of Málhildur."), false));
    pointsOfInterest.Add(FPointOfInterest(74.9957f, 42.1492f, "statue", "Statue of Freya", "Statue of the goddess Freya. Only thing left from a sunken village.", true));

    mapTiles.SetNum(MAP_TILES_SIZE);
}

Registering the Map model

The final step is of course to register the MapModel class we just created. This is as simple as it sounds - we will add the object, initialize it and use the View to create the model.

The StarterGuideHUD.h should now look like this:

class UPlayerModel;
class UMapModel;

UCLASS()
class COHERENTSAMPLE_API AStarterGuideHUD : public ACohtmlGameHUD
{
    GENERATED_BODY()

public:
    AStarterGuideHUD(const FObjectInitializer& PCIP);

    virtual void BeginPlay() override;

    void BindUI();

    UFUNCTION()
    void UpdateItemSelect();

    UPROPERTY()
    UPlayerModel* model;

    UPROPERTY()
    UMapModel* map;

private:
    cohtml::View* View;
};

And lastly, the StarterGuideHUD.cpp should look like this:

#include "StarterGuide/StarterGuideHUD.h"
#include "StarterGuide/PlayerModel.h"
#include "StarterGuide/MapModel.h"

#include "CohtmlGameHUD.h"

AStarterGuideHUD::AStarterGuideHUD(const FObjectInitializer& PCIP)
    : Super(PCIP)
{
    GetCohtmlHUD()->ReadyForBindings.AddDynamic(this, &AStarterGuideHUD::BindUI);
}

void AStarterGuideHUD::BeginPlay()
{
    Super::BeginPlay();
    model = NewObject<UPlayerModel>();
    map = NewObject<UMapModel>();
}

void AStarterGuideHUD::BindUI()
{
    View = GetCohtmlHUD()->GetView();
    if (!View)
    {
        UE_LOG(LogTemp, Error, TEXT("Failed to retrieve View!"));
        return;
    }

    View->CreateModel("PlayerModel", model);
    View->CreateModel("MapModel", map);
    View->SynchronizeModels();

    model->ItemSelectDelegate.AddDynamic(this, &AStarterGuideHUD::UpdateItemSelect);

    UE_LOG(LogTemp, Log, TEXT("UI is bound!"));
}

void AStarterGuideHUD::UpdateItemSelect()
{
    View->UpdateWholeModel(model);
    View->SynchronizeModels();
}

And here is the result: ue-chapter-4_1

ue-chapter-4_2

In the last chapter of this guide, we will implement the handling of events triggered from JavaScript.