Killing the player

We can kill enemies by jumping on them, but the player still can’t die. Let’s fix this.

We want to detect being hit by an enemy differently from squashing them. We want the player to die when they’re moving on the floor, but not if they’re in the air. We could use vector math to distinguish the two kinds of collisions. Instead, though, we will use an Area node, which works well for hitboxes.

Hitbox with the Area node

Head back to the Player scene and add a new Area node. Name it MobDetector. Add a CollisionShape node as a child of it.

In the Inspector, assign a cylinder shape to it.

Here is a trick you can use to make the collisions only happen when the player is on the ground or close to it. You can reduce the cylinder’s height and move it up to the top of the character. This way, when the player jumps, the shape will be too high up for the enemies to collide with it.

You also want the cylinder to be wider than the sphere. This way, the player gets hit before colliding and being pushed on top of the monster’s collision box.

The wider the cylinder, the more easily the player will get killed.

Next, select the MobDetector node again, and in the Inspector, turn off its Monitorable property. This makes it so other physics nodes cannot detect the area. The complementary Monitoring property allows it to detect collisions. Then, remove the Collision -> Layer and sets the mask to the “enemies” layer.

When areas detect a collision, they emit signals. We’re going to connect one to the Player node. In the Node tab, double-click the body_entered signal and connect it to the Player.

The MobDetector will emit body_entered when a KinematicBody or a RigidBody node enters it. As it only masks the “enemies” physics layers, it will only detect the Mob nodes.

Code-wise, we’re going to do two things: emit a signal we’ll later use to end the game and destroy the player. We can wrap these operations in a die() function that helps us put a descriptive label on the code.

GDScript

C#

# Emitted when the player was hit by a mob.
# Put this at the top of the script.
signal hit
# And this function at the bottom.
func die():
    emit_signal("hit")
    queue_free()
func _on_MobDetector_body_entered(_body):
    die()

// Don't forget to rebuild the project so the editor knows about the new signal.
// Emitted when the player was hit by a mob.
[Signal]
public delegate void Hit();
// ...
private void Die()
{
    EmitSignal(nameof(Hit));
    QueueFree();
}
// We also specified this function name in PascalCase in the editor's connection window
public void OnMobDetectorBodyEntered(Node body)
{
    Die();
}

Try the game again by pressing F5. If everything is set up correctly, the character should die when an enemy runs into it.

However, note that this depends entirely on the size and position of the Player and the Mob‘s collision shapes. You may need to move them and resize them to achieve a tight game feel.

Ending the game

We can use the Player‘s hit signal to end the game. All we need to do is connect it to the Main node and stop the MobTimer in reaction.

Open Main.tscn, select the Player node, and in the Node dock, connect its hit signal to the Main node.

Get and stop the timer in the _on_Player_hit() function.

GDScript

C#

func _on_Player_hit():
    $MobTimer.stop()

// We also specified this function name in PascalCase in the editor's connection window
public void OnPlayerHit()
{
    GetNode<Timer>("MobTimer").Stop();
}

If you try the game now, the monsters will stop spawning when you die, and the remaining ones will leave the screen.

You can pat yourself in the back: you prototyped a complete 3D game, even if it’s still a bit rough.

From there, we’ll add a score, the option to retry the game, and you’ll see how you can make the game feel much more alive with minimalistic animations.

Code checkpoint

Here are the complete scripts for the Main, Mob, and Player nodes, for reference. You can use them to compare and check your code.

Starting with Main.gd.

GDScript

C#

extends Node
export(PackedScene) var mob_scene
func _ready():
    randomize()
func _on_MobTimer_timeout():
    # Create a Mob instance and add it to the scene.
    var mob = mob_scene.instance()
    # Choose a random location on Path2D.
    var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
    # And give it a random offset.
    mob_spawn_location.unit_offset = randf()
    var player_position = $Player.transform.origin
    add_child(mob)
    mob.initialize(mob_spawn_location.translation, player_position)
func _on_Player_hit():
    $MobTimer.stop()

public class Main : Node
{
#pragma warning disable 649
    [Export]
    public PackedScene MobScene;
#pragma warning restore 649
    public override void _Ready()
    {
        GD.Randomize();
    }
    public void OnMobTimerTimeout()
    {
        // Create a mob instance and add it to the scene.
        var mob = (Mob)MobScene.Instance();
        // Choose a random location on Path2D.
        // We stire the reference to the SpawnLocation node.
        var mobSpawnLocation = GetNode<PathFollow>("SpawnPath/SpawnLocation");
        // And give it a random offset.
        mobSpawnLocation.UnitOffset = GD.Randf();
        Vector3 playerPosition = GetNode<Player>("Player").Transform.origin;
        AddChild(mob);
        mob.Initialize(mobSpawnLocation.Translation, playerPosition);
    }
    public void OnPlayerHit()
    {
        GetNode<Timer>("MobTimer").Stop();
    }
}

Next is Mob.gd.

GDScript

C#

extends KinematicBody
# Emitted when the player jumped on the mob.
signal squashed
# Minimum speed of the mob in meters per second.
export var min_speed = 10
# Maximum speed of the mob in meters per second.
export var max_speed = 18
var velocity = Vector3.ZERO
func _physics_process(_delta):
    move_and_slide(velocity)
func initialize(start_position, player_position):
    translation = start_position
    look_at(player_position, Vector3.UP)
    rotate_y(rand_range(-PI / 4, PI / 4))
    var random_speed = rand_range(min_speed, max_speed)
    velocity = Vector3.FORWARD * random_speed
    velocity = velocity.rotated(Vector3.UP, rotation.y)
 func squash():
    emit_signal("squashed")
    queue_free()
func _on_VisibilityNotifier_screen_exited():
    queue_free()

public class Mob : KinematicBody
{
    // Emitted when the played jumped on the mob.
    [Signal]
    public delegate void Squashed();
    // Minimum speed of the mob in meters per second
    [Export]
    public int MinSpeed = 10;
    // Maximum speed of the mob in meters per second
    [Export]
    public int MaxSpeed = 18;
    private Vector3 _velocity = Vector3.Zero;
    public override void _PhysicsProcess(float delta)
    {
        MoveAndSlide(_velocity);
    }
    public void Initialize(Vector3 startPosition, Vector3 playerPosition)
    {
        Translation = startPosition;
        LookAt(playerPosition, Vector3.Up);
        RotateY((float)GD.RandRange(-Mathf.Pi / 4.0, Mathf.Pi / 4.0));
        float randomSpeed = (float)GD.RandRange(MinSpeed, MaxSpeed);
        _velocity = Vector3.Forward * randomSpeed;
        _velocity = _velocity.Rotated(Vector3.Up, Rotation.y);
    }
    public void Squash()
    {
        EmitSignal(nameof(Squashed));
        QueueFree();
    }
    public void OnVisibilityNotifierScreenExited()
    {
        QueueFree();
    }
}

Finally, the longest script, Player.gd.

GDScript

C#

extends KinematicBody
# Emitted when a mob hit the player.
signal hit
# How fast the player moves in meters per second.
export var speed = 14
# The downward acceleration when in the air, in meters per second squared.
export var fall_acceleration = 75
# Vertical impulse applied to the character upon jumping in meters per second.
export var jump_impulse = 20
# Vertical impulse applied to the character upon bouncing over a mob in meters per second.
export var bounce_impulse = 16
var velocity = Vector3.ZERO
func _physics_process(delta):
    var direction = Vector3.ZERO
    if Input.is_action_pressed("move_right"):
        direction.x += 1
    if Input.is_action_pressed("move_left"):
        direction.x -= 1
    if Input.is_action_pressed("move_back"):
        direction.z += 1
    if Input.is_action_pressed("move_forward"):
        direction.z -= 1
    if direction != Vector3.ZERO:
        direction = direction.normalized()
        $Pivot.look_at(translation + direction, Vector3.UP)
    velocity.x = direction.x * speed
    velocity.z = direction.z * speed
    # Jumping.
    if is_on_floor() and Input.is_action_just_pressed("jump"):
        velocity.y += jump_impulse
    velocity.y -= fall_acceleration * delta
    velocity = move_and_slide(velocity, Vector3.UP)
    for index in range(get_slide_count()):
        var collision = get_slide_collision(index)
        if collision.collider.is_in_group("mob"):
            var mob = collision.collider
            if Vector3.UP.dot(collision.normal) > 0.1:
                mob.squash()
                velocity.y = bounce_impulse
func die():
    emit_signal("hit")
    queue_free()
func _on_MobDetector_body_entered(_body):
    die()

public class Player : KinematicBody
{
    // Emitted when the player was hit by a mob.
    [Signal]
    public delegate void Hit();
    // How fast the player moves in meters per second.
    [Export]
    public int Speed = 14;
    // The downward acceleration when in the air, in meters per second squared.
    [Export]
    public int FallAcceleration = 75;
    // Vertical impulse applied to the character upon jumping in meters per second.
    [Export]
    public int JumpImpulse = 20;
    // Vertical impulse applied to the character upon bouncing over a mob in meters per second.
    [Export]
    public int BounceImpulse = 16;
    private Vector3 _velocity = Vector3.Zero;
    public override void _PhysicsProcess(float delta)
    {
        var direction = Vector3.Zero;
        if (Input.IsActionPressed("move_right"))
        {
            direction.x += 1f;
        }
        if (Input.IsActionPressed("move_left"))
        {
            direction.x -= 1f;
        }
        if (Input.IsActionPressed("move_back"))
        {
            direction.z += 1f;
        }
        if (Input.IsActionPressed("move_forward"))
        {
            direction.z -= 1f;
        }
        if (direction != Vector3.Zero)
        {
            direction = direction.Normalized();
            GetNode<Spatial>("Pivot").LookAt(Translation + direction, Vector3.Up);
        }
        _velocity.x = direction.x * Speed;
        _velocity.z = direction.z * Speed;
        // Jumping.
        if (IsOnFloor() && Input.IsActionJustPressed("jump"))
        {
            _velocity.y += JumpImpulse;
        }
        _velocity.y -= FallAcceleration * delta;
        _velocity = MoveAndSlide(_velocity, Vector3.Up);
        for (int index = 0; index < GetSlideCount(); index++)
        {
            KinematicCollision collision = GetSlideCollision(index);
            if (collision.Collider is Mob mob && mob.IsInGroup("mob"))
            {
                if (Vector3.Up.Dot(collision.Normal) > 0.1f)
                {
                    mob.Squash();
                    _velocity.y = BounceImpulse;
                }
            }
        }
    }
    private void Die()
    {
        EmitSignal(nameof(Hit));
        QueueFree();
    }
    public void OnMobDetectorBodyEntered(Node body)
    {
        Die();
    }
}

See you in the next lesson to add the score and the retry option.