Bags and Banks

Documentation Unreal Engine Player Combat Inventory

A bag is an item that opens a container of its own, in a backpack or on a bag bar. A bank or a stash keeps items off the character until the player stands at it.

Set it up

5 minutes
  1. 1

    Give the character a pouch

    On BP_UPC_Character's InventoryComponent, set Config to InventoryConfig_UPC_SurvivalGrid (its Key Items list has Opens Bags ticked), and add Item_UPC_HipPouch to Starting Items; the case's filter keeps pouches out, so it lands in Key Items. If you cleared the belt's Filters in Use Only Part of the Inventory, restore them (Weapon, Consumable.Potion, Off Hand, Consumable) or the pouch also takes a belt slot.
    BP_UPC_Character
    ▾UPC
    ▾Inventory
    Config
    InventoryConfig_UPC_Simple▾
  2. 2

    Print a container's size when it changes

    Press + beside the component's On Capacity Changed:
    BP_UPC_Character · print a container's size when it changes
    On Capacity Changed (InventoryComponent)
    Container
    Get Container Size
    Target
    Container
    Return Value
    To String (IntPoint)
    In Int Point
    Return Value
    Print String
    In String
  3. 3

    Press Play

    The screen prints X=6 Y=1: the pouch opened its own container, six cells by one. Press I to see them under the case and drop an item there.

Make a bag

Give an item a Container fragment and Max Stack Size 1. Definition is the container it opens (own layout, rules, Access Tag); Container Tag names it (UPC.Inventory.Container.Bag by default, apart from the config's container tags). The bag opens in any container with Opens Bags ticked and stays closed elsewhere.
Details
Container
Container
Definition
Container_UPC_Pouch
Container Tag
UPC.Inventory.Container.Bag
The party RPG's pouch: in the backpack, which opens bags, it opens an eight slot container of its own.

Where a bag's items go

  • A bag keeps what it holds wherever it goes. Closed in storage, a chest or on the ground, it keeps its items in place, out of reach until it opens. Game code removing or consuming the bag spills them into other containers (Bags in detail, below).
  • A stack dropped on an open bag goes inside (Can Place answers Into Bag). A bag dropped on a bag trades places, so a bag bar reorders by drag.
  • A bag holding items never goes inside another bag (UPC.Inventory.Refused.BagNotEmpty): bags stay one level deep.
  • An item on the belt or in hand steps out of a bag that closes or leaves, into the carried containers. Drop a pouch holding a belted potion and a herb: the herb leaves in the pouch, the potion stays with the character.
  • A closed bag's items count as carried while the bag is (weight included) though out of reach until it opens. A pouch moved to the stash is closed and the stash is not carried, so its herb adds no weight.
  • A bag on the belt or in hand stays open, items in reach, even when Belt Space or Equipped Space Frees Its Place takes it out of the container that opened it.

A bag bar

For an MMO bag bar, a Slots container holds the bags that open, and the container they sit in stops opening them:
  1. Copy InventoryConfig_UPC_SurvivalGrid and its Container_UPC_KeyItems (an MMO's backpack would be the container bags sit in).
  2. In your Key Items copy, untick Opens Bags and point the copied config's Key Items row at it.
  3. Add a bar row after it: a Slots container with Opens Bags ticked and Takes New Items unticked (UPC.Inventory.Container.BagBar is a ready row tag).
  4. Set the copy as the character's Config. It has no screen row, so I opens the open world list; the key below needs no screen.
Details
Container_MyBagBar
Display
Display Name
Bag Bar
Icon
None
Layout
Layout
Slots
Slot Count
4
Capacity Tag
None
Rules
Rules
0 Array elements
Access
Carried
Takes New Items
Access Tag
None
Bags
Opens Bags
Four slots for bags. A bag placed here opens its own container, which adds fill right after the backpack.
A screen moves a bag onto the bar with Request Move, and On Capacity Changed fires as its container opens. The demo screens show no bag bar, so a key stands in for the drag. The destination names the bar by tag alone: Providing Item stays empty for a config-listed container and names the bag only for a bag's own container (Read bags in a screen).
BP_UPC_Character · B puts the pouch on the bag bar
B
Pressed
Released
Key
Inventory Component
Find First Item by Definition
Target
Item DefItem_UPC_HipPouch
Return Value
Make UPC Container Id
TagUPC.Inventory.Container.BagBar
Providing Item
UPC Container Id
Make UPC Inventory Placement
Container
Position0
Rotated
UPC Inventory Placement
Request Move
Target is UPC Inventory
Target
Item
Count1
Destination

A bank or a stash

A bank or stash is a container of the player's inventory with Carried and Takes New Items off and an Access Tag (the demo's Stash uses UPC.State.AtStash). The character reaches it only while holding that tag, so grant it on the server while the character stands at the bank and remove it on leaving. The demo's BP_UPC_StorageBox does this with GE_UPC_StorageAccess while the character stands in its zone. The box holds nothing: the stash belongs to the player's inventory and stays across inventory styles (Survival Grid Inventory).
Details
Container_UPC_Stash
Display
Display Name
Stash
Icon
None
Layout
Layout
Slots
Slot Count
30
Rules
Rules
0 Array elements
Access
Carried
Takes New Items
Access Tag
UPC.State.AtStash
Bags
Opens Bags
The stash every demo style lists: thirty slots off the character that a player fills by moving items in, reached only while the character holds UPC.State.AtStash.

Read bags in a screen

A bag's container goes by a UPC Container Id: its Tag plus Providing Item (the bag), so two pouches of one kind stay apart; a gameplay tag wired into a container pin converts automatically. Get Containers lists each open bag right after the container it sits in, the order a pickup fills them. Get Container Opened By answers a bag's container for a bag bar slot (false while closed).

Debug it

  • A bag whose Container Tag a config row uses opens nothing, and LogUPCInventory warns once.
  • Saving a bag item fails for a Max Stack Size above 1, no Container Tag, or a Definition that opens bags.
AdvancedBags in detail
  • A bag's items are in reach only while the bag is open, in reach, and its container's Access Tag allows. Moves, uses, draws, consumes, sorts, transfers and adds skip a closed bag's items.
  • A bag inside a bag never opens, and a bag never goes into its own container (OutOfBounds).
  • A drop on a closed bag is a drop on a plain item. Into Bag goes to the bag's first free place, judged by its container's rules and the carry rules.
  • Remove Item Instance, Consume Item or Consume Item Instance on a bag spills its contents: each stack moves whole, stat tags and belt slot kept, to where an add would put it, else past the end of the first carried container taking new items, with a warning. Nothing drops into the world. Take Item Out moves a bag elsewhere with its items.
  • The carry rules judge a bag arriving from storage together with its items, so a full pouch too heavy to carry stays in the stash with TooHeavy.
  • Request Transfer and Request Take All move a bag and its items to or from a chest whole or not at all; in the chest the bag is closed and the chest lists the bag alone.
  • A drop, a rack's Put Back and Take Item Out take a bag out with its items; picking it up restores them in place (Can Add Bag With Items answers first).
  • A spilled stack from the belt or hand goes only to a carried container. Where no container opens bags (the open world list), a bag's items stay out of reach.
MultiplayerWhat runs where
  • A bag's items reach the owning player's machine only; a chest's or a dropped bag's reach every machine near it. Items can arrive before the bag; each announces its add once the bag has arrived.
C++C++
  • UUPCItemFragment_Container makes an item a bag; UUPCContainerDefinition::bOpensBags makes a container open bags.
  • FUPCContainerId holds Tag and ProvidingItem; UUPCInventoryStatics adds the tag conversion and the equality node.
  • UUPCInventoryComponent::GetContainerOpenedBy(Bag, OutContainer) and GetContainers() are the queries a bag bar screen reads; TakeItemOut(Item, Count, OutBagItems) hands a bag's items back as FUPCInventorySnapshot rows for whatever takes the bag.