Backpack

A slot inventory with stacks, item fragments, and an optional shape grid for Unreal Engine.

👀 Summary

NsBackpack is a slot inventory for gameplay programmers. An actor gets a backpack component with a fixed number of slots. Each slot holds an item, a quantity, and optional item data. An item is a data asset with a name, an icon, a mesh, a stack size, and fragments that your game makes. The optional NsBackpackGrid module puts the slots in a grid, where an item covers the cells of its shape.

NsBackpack has no UI, no selected slot, no item use, no crafting, and no save system. It has no server RPCs, so your game sends the change requests to the server. NsBackpack depends on no other plugin.

📦 Features

• Slots and stacks: Add, remove, count, find, and move items. Stacks fill before empty slots.
• Item assets: One data asset for each kind of item, with a display name, an icon, a world mesh, and a stack size.
• Fragments: Put game data on an item as instanced fragment objects, and find them by class.
• Item state: Keep the state of one item, such as durability, in an instanced struct on its slot.
• Slot rules: Override CanAccept and CanStack in C++ or Blueprint.
• Start items: Give a backpack its items when play starts.
• Replication: The server changes the slots, and the slots replicate to every machine.
• Shape grid: Items with a Grid Shape fragment cover a box or any set of cells, and turn by quarter turns.

⚙️ Requirements

Unreal Engine 5.7+

🛠️ Installation

1. Clone or download this repository.
2. Copy the NsBackpack folder into the Plugins folder of your project.
3. Add "NsBackpack" to the dependencies of your game module in Build.cs. Add "NsBackpackGrid" too for a grid.
4. Generate the project files and enable the plugin.

🚀 Getting Started

1. Make an item: Content Browser > Miscellaneous > Data Asset > NsBackpackItemDefinition.
2. Set Display Name and Max Stack on the item.
3. Add a UNsBackpackComponent to your character.
4. On the server, call Add Item with the item and a quantity.
5. Bind On Changed to update your UI.

In C++:

#include "NsBackpackComponent.h"

// In the constructor of the character
Backpack = CreateDefaultSubobject<UNsBackpackComponent>(TEXT("Backpack"));

// On the server. The return value is the quantity that did not fit.
const int32 Left = Backpack->AddItem(BoltItem, 15);

🧩 Modules

🔧 API

• UNsBackpackComponent – The slots. AddItem, RemoveItem, RemoveFromSlot, MoveSlot, SetSlot, CountItem, FindItem, FindEmptySlot, and OnChanged.
• UNsBackpackItemDefinition – The data asset of one kind of item. FindFragment returns its first fragment of a class.
• UNsBackpackItemFragment – The abstract base class of game data on an item.
• FNsBackpackSlot – An item, a quantity, and an FInstancedStruct of item data.
• UNsBackpackGridComponent – A backpack with its slots in a grid. PlaceItem, MoveItem, RotateItem, CanPlace, FindPlacement, and GetCellOwner.
• UNsBackpackGridShape – The Grid Shape fragment: a box size and the cells inside the box.

🚧 Limits

• Only the server, or a backpack without an owner, can change the slots. The change functions do nothing on a client.
• The number of slots stays fixed until the next ResetSlots or ResetGrid call.
• A slot with item data does not stack.
• A grid move never swaps two items.
• The grid builds its cell map again on each query.

📚 Documentation

Contact

E-mail LinkedIn GitHub Bluesky