We will define a new class, AMeleeWeapon (derived from AActor), to represent hand-held combat weapons. I will attach a couple of blueprint-editable properties to the AMeleeWeapon class, and the AMeleeWeapon class will look as shown in the following code:

class AMonster;

UCLASS()
class GOLDENEGG_API AMeleeWeapon : public AActor
{
  GENERATED_UCLASS_BODY()

  // The amount of damage attacks by this weapon do
  UPROPERTY(EditAnywhere, BlueprintReadWrite, Category =  MeleeWeapon)
  float AttackDamage;

  // A list of things the melee weapon already hit this swing
  // Ensures each thing sword passes thru only gets hit once
  TArray<AActor*> ThingsHit;

  // prevents damage from occurring in frames where
  // the sword is not swinging
  bool Swinging;

  // "Stop hitting yourself" - used to check if the 
  // actor holding the weapon is hitting himself
  AMonster *WeaponHolder;

  // bounding box that determines when melee weapon hit
  UPROPERTY(VisibleDefaultsOnly, BlueprintReadOnly, Category =  MeleeWeapon)
  UBoxComponent* ProxBox;

  UPROPERTY(VisibleDefaultsOnly, BlueprintReadOnly, Category =  MeleeWeapon)
  UStaticMeshComponent* Mesh;

  UFUNCTION(BlueprintNativeEvent, Category = Collision)
  void Prox( AActor* OtherActor, UPrimitiveComponent* OtherComp,  int32 OtherBodyIndex, bool bFromSweep, const FHitResult &  SweepResult );
  void Swing();
  void Rest();
};

Notice how I used a bounding box for ProxBox, and not a bounding sphere. This is because swords and axes will be better approximated by boxes rather than spheres. There are two member functions, Rest() and Swing(), which let MeleeWeapon know what state the actor is in (resting or swinging). There's also a TArray<AActor*> ThingsHit property inside this class that keeps track of the actors hit by this melee weapon on each swing. We are programming it so that the weapon can only hit each thing once per swing.

The AMeleeWeapon.cpp file will contain just a basic constructor and some simple code to send damages to OtherActor when our sword hits him. We will also implement the Rest() and Swing() functions to clear the list of things hit. The MeleeWeapon.cpp file has the following code:

AMeleeWeapon::AMeleeWeapon(const class FObjectInitializer& PCIP) :  Super(PCIP)
{
  AttackDamage = 1;
  Swinging = false;
  WeaponHolder = NULL;

  Mesh = PCIP.CreateDefaultSubobject<UStaticMeshComponent>(this,  TEXT("Mesh"));
  RootComponent = Mesh;

  ProxBox = PCIP.CreateDefaultSubobject<UBoxComponent>(this,  TEXT("ProxBox"));
  ProxBox->OnComponentBeginOverlap.AddDynamic( this,  &AMeleeWeapon::Prox );
  ProxBox->AttachTo( RootComponent );
}

void AMeleeWeapon::Prox_Implementation( AActor* OtherActor,  UPrimitiveComponent* OtherComp, int32 OtherBodyIndex, bool  bFromSweep, const FHitResult & SweepResult )
{
  // don't hit non root components
  if( OtherComp != OtherActor->GetRootComponent() )
  {
    return;
  }

  // avoid hitting things while sword isn't swinging,
  // avoid hitting yourself, and
  // avoid hitting the same OtherActor twice
  if( Swinging && OtherActor != WeaponHolder &&  !ThingsHit.Contains(OtherActor) )
  {
    OtherActor->TakeDamage( AttackDamage + WeaponHolder- >BaseAttackDamage, FDamageEvent(), NULL, this );
    ThingsHit.Add( OtherActor );
  }
}
void AMeleeWeapon::Swing()
{
  ThingsHit.Empty();  // empty the list
  Swinging = true;
}
void AMeleeWeapon::Rest()
{
  ThingsHit.Empty();
  Swinging = false;
}

To complete this exercise, we need a sword to put into the model's hand. I added a sword to the project called Kilic from http://tf3dm.com/3d-model/sword-95782.html by Kaan Gülhan. The following is a list of other places where you will get free models:

TurboSquid's search for free swords

I had to edit the kilic sword mesh slightly to fix the initial sizing and rotation. You can import any mesh in the Filmbox (FBX) format into your game. The kilic sword model is in the sample code package for Chapter 11, Monsters.

To import your sword into the UE4 editor, right-click on any folder you want to add the model to. Navigate to New Asset | Import to | Game | Models..., and from the file explorer that pops up, select the new asset you want to import. If a Models folder doesn't exist, you can create one by simply right-clicking on the tree view at the left and selecting New Folder in the pane on the left-hand side of the Content Browser tab. I selected the kilic.fbx asset from my desktop.

Importing to your project

Inside the UE4 editor, create a blueprint based off of AMeleeWeapon called BP_MeleeSword. Configure BP_MeleeSword to use the kilic blade model (or any blade model you choose), as shown in the following screenshot:

The ProxBox class will determine whether something was hit by the weapon, so we will modify the ProxBox class such that it just encloses the blade of the sword, as shown in the following screenshot:

Also, under the Collision Presets panel, it is important to select the NoCollision option for the mesh (not BlockAll). This is illustrated in the following screenshot:

If you select BlockAll, then the game engine will automatically resolve all the interpenetration between the sword and the characters by pushing away things that the sword touches whenever it is swung. The result is that your characters will appear to go flying whenever a sword is swung.

A UE4 blueprint is a visual realization of the code (not to be confused with how sometimes people say that a C++ class is a metaphorical blueprint of a class instance). In UE4 blueprints, instead of actually writing code, you drag and drop elements onto a graph and connect them to achieve desired play. By connecting the right nodes to the right elements, you can program anything you want in your game.

Let's start writing a sample blueprint to get a feel how they work. First, click on the blueprint menu bar at the top and select Open Level Blueprint, as shown in the following screenshot:

The Level Blueprint option executes automatically when you begin the level. Once you open this window, you should see a blank slate to create your gameplay on, as shown here:

Right-click anywhere on the graph paper. Start typing begin and click on the Event Begin Play option from the drop-down list that appears. Ensure that the Context Sensitive checkbox is checked, as shown in the following screenshot:

Immediately after you click on the Event Begin Play option, a red box will appear on your screen. It has a single white pin at the right-hand side. This is called the execution pin, as shown here:

The first thing that you need to know about animation blueprints is the white pin execution path (the white line). If you've seen a blueprint graph before, you must have noticed a white line going through the graph, as shown in the following diagram:

The white pin execution path is pretty much equivalent to having lines of code lined up and run one after the other. The white line determines which nodes will get executed and in what order. If a node does not have a white execution pin attached to it, then that node will not get executed at all.

Drag off the white execution pin from Event Begin Play. Start by typing draw debug box in the Executable actions dialog. Select the first thing that pops up (f Draw Debug Box), as shown here:

Fill in some details for how you want the box to look. Here, I selected the color blue for the box, the center of the box at (0, 0, 100), the size of the box to be (200, 200, 200), and a duration of 180 seconds (be sure to enter a duration that is long enough to see the result), as shown in the following screenshot:

Now click on the Play button to realize the graph. Remember that you have to find the world's origin to see the debug box.

Find the world's origin by placing a golden egg at (0, 0, (some z value)), as shown in the following screenshot:

This is how the box will look in the level:

A debug box rendered at the origin

To integrate our attack animation, we have to modify the blueprint. Under Content Browser, open up MixamoAnimBP_Adam.

The first thing you'll notice is that the graph has two sections: a top section and a bottom section. The top section is marked "Basic Character movement...," while the bottom section says "Mixamo Example Character Animation...." Basic character movement is in charge of the walking and running movements of the model. We will be working in the Mixamo Example Character Animation with Attack and Jump section, which is responsible for the attack animation. We will be working in the latter section of the graph, shown in the following screenshot:

When you first open the graph, it starts out by zooming in on a section near the bottom. To scroll up, right-click the mouse and drag it upwards. You can also zoom out using the mouse wheel or by holding down the Alt key and the right mouse button while moving the mouse up.

Before proceeding, you might want to duplicate the MixamoAnimBP_Adam resource so that you don't damage the original, in case you need to go back and change something later. This allows you to easily go back and correct things if you find that you've made a mistake in one of your modifications, without having to reinstall a fresh copy of the whole animation package into your project.

Making a duplicate of the MixamoAnimBP_Adam resource to avoid damaging the original asset

We're going to do only a few things to make Adam swing the sword when he is attacking. Let's do it in order.

if( Monster.isInAttackRangeOfPlayer() )
{
  Monster.Animation = The Attack Animation;
}

Test your animation. The monster should swing only when he is within the player's range.

We want to add an animation notify event when the sword is swung. First, declare and add a blueprint callable C++ function to your Monster class:

// in Monster.h:
UFUNCTION( BlueprintCallable, Category = Collision )
void SwordSwung();

The BlueprintCallable statement means that it will be possible to call this function from blueprints. In other words, SwordSwung() will be a C++ function that we can invoke from a blueprints node, as shown here:

// in Monster.cpp
void AMonster::SwordSwung()
{
  if( MeleeWeapon )
  {
    MeleeWeapon->Swing();
  }
}

Next open the Mixamo_Adam_Sword_Slash animation by double-clicking on it from your Content Browser (it should be in MixamoAnimPack/Mixamo_Adam/Anims/Mixamo_Adam_Sword_Slash). Scrub the animation to the point where Adam starts swinging his sword. Right-click on the animation bar and select New Notify under Add Notify..., as shown in the following screenshot:

Name the notification SwordSwung:

The notification name should appear in your animation's timeline, shown as follows:

Save the animation and then open up your version of MixamoAnimBP_Adam again. Underneath the SET group of nodes, create the following graph:

The AnimNotify_SwordSwung node appears when you right-click in the graph (with Context Sensitive turned on) and start typing SwordSwung. The Cast To Monster node is again fed in from the Try Get Pawn Owner node as in step 2 of the Modifying the animation blueprint for Mixamo Adam section. Finally, Sword Swung is our blueprint-callable C++ function in the AMonster class.

If you start the game now, your monsters will execute their attack animation whenever they actually attack. When the sword's bounding box comes in contact with you, you should see your HP bar go down a bit (recall that the HP bar was added at the end of Chapter 8, Actors and Pawns, as an exercise).

Monsters attacking the player