Inventory System

Inventory Systems in Godot 4.3+

All examples target Godot 4.3+ with no deprecated APIs. GDScript is shown first, then C#.

> Related skills: resource-pattern for custom Resource data containers, save-load for inventory serialization, event-bus for inventory change notifications, hud-system for inventory UI display.

---

1. Architecture Overview

┌─────────────────────────────────────────────────────────┐
│                        UI Layer                         │
│   InventoryUI (Control)                                 │
│     └─ GridContainer                                    │
│           └─ SlotUI × N (Button)                        │
│                 └─ TextureRect (icon) + Label (qty)     │
│                                                         │
│   Connects to: inventory_changed signal                 │
│   Drag-and-drop via _get_drag_data / _drop_data         │
└───────────────────────┬─────────────────────────────────┘
                        │ reads / mutates
┌───────────────────────▼─────────────────────────────────┐
│                    Inventory (Node)                      │
│   slots: Array[InventorySlot]                           │
│   add_item(item, qty) → leftover: int                   │
│   remove_item(item, qty)                                │
│   has_item(item, qty) → bool                            │
│   get_item_count(item) → int                            │
│                                                         │
│   signals: inventory_changed                            │
│             item_added(item, quantity)                  │
│             item_removed(item, quantity)                │
└───────────────────────┬─────────────────────────────────┘
                        │ references
┌───────────────────────▼─────────────────────────────────┐
│                   Data Layer (Resources)                 │
│   ItemData (Resource)                                   │
│     id, name, description, icon, max_stack_size,        │
│     item_type enum                                      │
│                                                         │
│   InventorySlot (inner class / Resource)                │
│     item: ItemData, quantity: int                       │
└─────────────────────────────────────────────────────────┘

---

2. ItemData Resource

Define items as Resources so they live in .tres files, are shareable across scenes, and benefit from full editor integration.

GDScript

# item_data.gd
class_name ItemData
extends Resource

enum ItemType {
    CONSUMABLE,
    EQUIPMENT,
    MATERIAL,
    KEY_ITEM,
}

@export var id: String = ""
@export var name: String = ""
@export var description: String = ""
@export var icon: Texture2D
@export var max_stack_size: int = 99
@export var item_type: ItemType = ItemType.MATERIAL

Create item assets: res://items/potion_health.tres, set id = "potion_health", etc.

C#

// ItemData.cs
using Godot;

[GlobalClass]
public partial class ItemData : Resource
{
    public enum ItemType
    {
        Consumable,
        Equipment,
        Material,
        KeyItem,
    }

    [Export] public string Id          { get; set; } = "";
    [Export] public string Name        { get; set; } = "";
    [Export] public string Description { get; set; } = "";
    [Export] public Texture2D Icon     { get; set; }
    [Export] public int MaxStackSize   { get; set; } = 99;
    [Export] public ItemType Type      { get; set; } = ItemType.Material;
}

> Use [GlobalClass] so the Inspector dropdown shows ItemData as a resource type when creating .tres files.

---

3. Inventory Class

GDScript

# inventory.gd
class_name Inventory
extends Node

signal inventory_changed
signal item_added(item: ItemData, quantity: int)
signal item_removed(item: ItemData, quantity: int)

@export var capacity: int = 20

var slots: Array[InventorySlot] = []

func _ready() -> void:
    slots.resize(capacity)
    for i in capacity:
        slots[i] = InventorySlot.new()

# Returns the number of items that could NOT be added (leftover).
func add_item(item: ItemData, quantity: int = 1) -> int:
    var remaining := quantity

    # Fill existing stacks first
    for slot in slots:
        if remaining  0:
        item_added.emit(item, added)
        inventory_changed.emit()

    return remaining

func remove_item(item: ItemData, quantity: int = 1) -> void:
    var remaining := quantity

    for slot in slots:
        if remaining  0:
        item_removed.emit(item, actually_removed)
        inventory_changed.emit()

func has_item(item: ItemData, quantity: int = 1) -> bool:
    return get_item_count(item) >= quantity

func get_item_count(item: ItemData) -> int:
    var total := 0
    for slot in slots:
        if not slot.is_empty() and slot.item == item:
            total += slot.quantity
    return total

C#

// Inventory.cs
using Godot;
using Godot.Collections;

public partial class Inventory : Node
{
    [Signal] public delegate void InventoryChangedEventHandler();
    [Signal] public delegate void ItemAddedEventHandler(ItemData item, int quantity);
    [Signal] public delegate void ItemRemovedEventHandler(ItemData item, int quantity);

    [Export] public int Capacity { get; set; } = 20;

    public Array Slots { get; private set; } = new();

    public override void _Ready()
    {
        for (int i = 0; i Returns the number of items that could NOT be added (leftover).
    public int AddItem(ItemData item, int quantity = 1)
    {
        int remaining = quantity;

        // Fill existing stacks first
        foreach (var slot in Slots)
        {
            if (remaining  0)
        {
            EmitSignal(SignalName.ItemAdded, item, added);
            EmitSignal(SignalName.InventoryChanged);
        }

        return remaining;
    }

    public void RemoveItem(ItemData item, int quantity = 1)
    {
        int remaining = quantity;

        foreach (var slot in Slots)
        {
            if (remaining  0)
        {
            EmitSignal(SignalName.ItemRemoved, item, actuallyRemoved);
            EmitSignal(SignalName.InventoryChanged);
        }
    }

    public bool HasItem(ItemData item, int quantity = 1)
        => GetItemCount(item) >= quantity;

    public int GetItemCount(ItemData item)
    {
        int total = 0;
        foreach (var slot in Slots)
            if (!slot.IsEmpty() && slot.Item == item)
                total += slot.Quantity;
        return total;
    }
}

---

4. InventorySlot

InventorySlot is a lightweight object tracking an item reference and its quantity. Define it as an inner class on Inventory (GDScript) or as a standalone RefCounted subclass (C#).

GDScript

# inventory_slot.gd  — or nest as inner class inside inventory.gd
class_name InventorySlot
extends RefCounted

var item: ItemData = null
var quantity: int   = 0

func is_empty() -> bool:
    return item == null or quantity  bool:
    return not is_empty() and item == new_item and quantity  int:
    if item == null:
        push_error("InventorySlot.add_to_stack: slot has no item assigned")
        return amount
    var space    := item.max_stack_size - quantity
    var to_add   := mini(amount, space)
    quantity     += to_add
    return amount - to_add

# Removes amount from this slot. Clears the slot when quantity reaches zero.
func remove_from_stack(amount: int) -> void:
    quantity -= amount
    if quantity  Item == null || Quantity  !IsEmpty() && Item == newItem && Quantity Adds amount to this slot. Returns leftover that did not fit.
    public int AddToStack(int amount)
    {
        if (Item == null)
        {
            GD.PushError("InventorySlot.AddToStack: slot has no item assigned");
            return amount;
        }
        int space  = Item.MaxStackSize - Quantity;
        int toAdd  = Mathf.Min(amount, space);
        Quantity  += toAdd;
        return amount - toAdd;
    }

    /// Removes amount from this slot. Clears when quantity reaches zero.
    public void RemoveFromStack(int amount)
    {
        Quantity -= amount;
        if (Quantity  See [references/equipment.md](references/equipment.md) for the full GDScript and C# `Equipment` class with `EquipmentSlotType` enum, equip / unequip API, and stat aggregation.

---

## 6. UI Binding

Slot-grid UI: a `GridContainer` of `Panel` slot widgets, each rendering one `InventorySlot`. Drag-and-drop uses `_get_drag_data` / `_drop_data` / `_can_drop_data` on the slot widget. The Inventory emits `inventory_changed`; the UI re-renders affected slots.

> See [references/ui-binding.md](references/ui-binding.md) for the full GDScript and C# slot widget (drag/drop, hover preview), inventory grid layout, and tooltip wiring.

---

## 7. Serialization

Persist Inventory + Equipment as a Dictionary keyed by item resource path (since ItemData lives at `res://items/.tres`). Reload by `load(path)` and reconstructing the slot list. Version field gates migration on load.

> See [references/serialization.md](references/serialization.md) for the GDScript and C# save/load implementation with `version` field and ConfigFile / JSON variants.

---

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [jame581](https://github.com/jame581)
- **Source:** [jame581/GodotPrompter](https://github.com/jame581/GodotPrompter)
- **License:** MIT

Install and usage instructions live in the source repository linked above.