godot-combat-system

What this skill does

# Combat System

Expert guidance for building flexible, component-based combat systems.

## NEVER Do

- **NEVER use direct damage references (`target.health -= 10`)** — This bypasses armor, resistances, and invincibility logic. Always use a `DamageData` + `HealthComponent` pattern for consistent results.
- **NEVER forget invincibility frames (i-frames)** — Without them, multi-hit attacks deal damage every single frame. Always apply a brief invincibility period (0.1–0.5s) after taking a hit.
- **NEVER keep hitboxes active permanently** — This causes unintended "ghost" damage. Enable and disable hitboxes precisely using `AnimationPlayer` tracks or code-timed triggers.
- **NEVER use groups for physics-based hit filtering** — Collision layers are evaluated in C++ and are significantly faster. Groups don't restrict physics intersections adequately for high-performance combat.
- **NEVER emit damage signals without a DamageData object** — A raw number loses critical context like damage type, source, and knockback direction.
- **NEVER use try/catch blocks with validate targets** — GDScript does not support exceptions. Use `has_method(&"take_damage")` or the `is` operator for safe type checking.
- **NEVER hardcode hitstun pauses using OS.delay_msec()** — This blocks the entire OS thread and freezes the game. Use `create_tween()` or `Engine.time_scale` for visual hit-stop effects.
- **NEVER apply massive impulses to a RigidBody inside _process()** — Physics-altering impulses must happen in `_physics_process()` or `_integrate_forces()` to remain deterministic and stable.
- **NEVER couple UI lifebars directly inside the Player script** — Use a `health_changed` signal. This keeps your combat logic clean and independent of UI implementation details.
- **NEVER leave CollisionShapes active on dead entities** — Corpses will block players and towers. Disable them immediately using `set_deferred("disabled", true)`.
- **NEVER scale CollisionShapes non-uniformly** — Non-uniform scaling breaks the physics engine's collision math. Always scale the internal resource (e.g., `CircleShape2D.radius`) instead.
- **NEVER use instanced Nodes for base stat data** — Nodes carry unnecessary overhead. Use Godot's `Resource` class for lightweight, efficient, and inspectable stat containers.
- **NEVER use raw strings for elemental damage types** — Strings are slow and error-prone. Use `enum` flags (optionally with `@export_flags`) to manage multi-type damage efficiently.
- **NEVER use standard strings for state names in high-frequency loops** — Use `StringName` (&"attacking", &"stunned") to drastically improve dictionary lookups and hash comparison speeds.
- **NEVER forget to duplicate() a shared Resource stats block** — If you don't call `duplicate()` when instancing a mob, all enemies of that type will share the same health pool.

---

## Available Scripts

> **MANDATORY**: Read the appropriate script before implementing the corresponding pattern.

### [combat_system_patterns.gd](scripts/combat_system_patterns.gd)
10 Expert patterns: Safe duck-typing, hitstun tweens, nodeless AoE shape casting, and frame-perfect sync.

### [hitbox_hurtbox.gd](scripts/hitbox_hurtbox.gd)
Component-based hitbox with hit-stop and knockback logic.

---

## Damage System

```gdscript
# damage_data.gd
class_name DamageData
extends RefCounted

var amount: float
var source: Node
var damage_type: String = "physical"
var knockback: Vector2 = Vector2.ZERO
var is_critical: bool = false

func _init(dmg: float, src: Node = null) -> void:
    amount = dmg
    source = src
```

## Hurtbox/Hitbox Pattern

```gdscript
# hurtbox.gd
extends Area2D
class_name Hurtbox

signal damage_received(data: DamageData)

@export var health_component: Node

func _ready() -> void:
    area_entered.connect(_on_area_entered)

func _on_area_entered(area: Area2D) -> void:
    if area is Hitbox:
        var damage := area.get_damage()
        damage_received.emit(damage)
        
        if health_component:
            health_component.take_damage(damage)
```

```gdscript
# hitbox.gd
extends Area2D
class_name Hitbox

@export var damage: float = 10.0
@export var damage_type: String = "physical"
@export var knockback_force: float = 100.0
@export var owner_node: Node

func get_damage() -> DamageData:
    var data := DamageData.new(damage, owner_node)
    data.damage_type = damage_type
    
    # Calculate knockback direction
    if owner_node:
        var direction := (global_position - owner_node.global_position).normalized()
        data.knockback = direction * knockback_force
    
    return data
```

## Health Component

```gdscript
# health_component.gd
extends Node
class_name HealthComponent

signal health_changed(old_health: float, new_health: float)
signal died
signal healed(amount: float)

@export var max_health: float = 100.0
@export var current_health: float = 100.0
@export var invincible: bool = false

func take_damage(data: DamageData) -> void:
    if invincible:
        return
    
    var old_health := current_health
    current_health -= data.amount
    current_health = clampf(current_health, 0, max_health)
    
    health_changed.emit(old_health, current_health)
    
    if current_health <= 0:
        died.emit()

func heal(amount: float) -> void:
    var old_health := current_health
    current_health += amount
    current_health = minf(current_health, max_health)
    
    healed.emit(amount)
    health_changed.emit(old_health, current_health)

func is_dead() -> bool:
    return current_health <= 0
```

## Combat State Machine

```gdscript
# combat_state.gd
extends Node
class_name CombatState

enum State { IDLE, ATTACKING, BLOCKING, DODGING, STUNNED }

var current_state: State = State.IDLE
var can_act: bool = true

func enter_attack_state() -> bool:
    if not can_act:
        return false
    
    current_state = State.ATTACKING
    can_act = false
    return true

func enter_block_state() -> void:
    current_state = State.BLOCKING

func enter_dodge_state() -> bool:
    if not can_act:
        return false
    
    current_state = State.DODGING
    can_act = false
    return true

func exit_state() -> void:
    current_state = State.IDLE
    can_act = true
```

## Combo System

```gdscript
# combo_system.gd
extends Node
class_name ComboSystem

signal combo_executed(combo_name: String)

@export var combo_window: float = 0.5
var combo_buffer: Array[String] = []
var last_input_time: float = 0.0

func register_input(action: String) -> void:
    var current_time := Time.get_ticks_msec() / 1000.0
    
    if current_time - last_input_time > combo_window:
        combo_buffer.clear()
    
    combo_buffer.append(action)
    last_input_time = current_time
    
    check_combos()

func check_combos() -> void:
    # Light → Light → Heavy = Special Attack
    if combo_buffer.size() >= 3:
        var last_three := combo_buffer.slice(-3)
        if last_three == ["light", "light", "heavy"]:
            execute_combo("special_attack")
            combo_buffer.clear()

func execute_combo(combo_name: String) -> void:
    combo_executed.emit(combo_name)
```

## Ability System

```gdscript
# ability.gd
class_name Ability
extends Resource

@export var ability_name: String
@export var cooldown: float = 1.0
@export var damage: float = 25.0
@export var range: float = 100.0
@export var animation: String

var is_on_cooldown: bool = false

func can_use() -> bool:
    return not is_on_cooldown

func use(caster: Node) -> void:
    if not can_use():
        return
    
    is_on_cooldown = true
    
    # Execute ability logic
    _execute(caster)
    
    # Start cooldown
    await caster.get_tree().create_timer(cooldown).timeout
    is_on_cooldown = false

func _execute(caster: Node) -> void:
    # Override in derived abilities
    pass
```

## Damage Popups

```gdscript
# damage_popup.gd
extends Label

func show_damage(amount: float, is_crit: bool = false) -> void:
    text = str(int(amount))
    
    if is_crit:
        modulate = Color.RED