Containers and Rules

Documentation Unreal Engine Player Combat Inventory

An inventory config gives a character its containers, such as a backpack of slots, a grid case or a bank, and limits on what it carries, such as a weight limit that tags the character Overburdened.

Set it up

5 minutes

1
Give the potion a weight
Follow the Inventory quick start first (three Item_MyPotion at start), then add a Weight fragment with Weight 25 to Item_MyPotion.
2
Give the character a config that weighs it
On BP_UPC_Character's InventoryComponent, set Config to Demo/Items/Inventory/InventoryConfig_UPC_OpenWorldList. Its first carry rule, a Weight Limit of 60 with Refuse Over Limit off, lets everything in and puts UPC.State.Overburdened on the character once the load reaches 60. Open World List shows its other settings.
BP_UPC_Character
▾UPC
▾Inventory
Config
InventoryConfig_UPC_Simple▾
3
Press Play, then drink
Three potions weigh 75, so the character cannot move: its UPC Speed Modifier scales walking to 0 under Overburdened and UPC Sprint blocks on the tag. With no belt on the open world list, drink from the inventory screen: press I, pick the potion, press E (Consume). The load drops to 50, the tag comes off, and closing the screen with I lets the character walk.

Make a config

Right-click in the Content Browser, UPC, Items, Inventory Config.
Add a Containers row per container: a gameplay tag naming it and a Container Definition (UPC, Items) laying it out.
Set the config on the character's InventoryComponent. A config the screens component does not list opens the fallback screen (Inventory Screens).

Adds and pickups try the containers in this order; what fits nowhere stays out. The survival grid lists the case first and filters keys and pouches out of it, so they go on to the key items list.

Details

Container_UPC_Case

Display

Display Name

Case

Icon

None

Layout

Grid

Grid Size

6.0

4.0

Allow Rotation

Capacity Tag

UPC.Inventory.Capacity.CaseRows

Rules

1 Array element

Index [ 0 ]

Item Filter

Allowed Tags

0 Gameplay Tags

Blocked Tags

2 Gameplay Tags

UPC.Slot.KeyItem

UPC.Slot.Upgrade

Access

Carried

Takes New Items

Access Tag

None

Bags

Opens Bags

Six columns by four rows, where an item may lie turned. Keys and pouches stay out through its filter. Each point of UPC.Inventory.Capacity.CaseRows the character owns adds a row.

Setting	Does
Display Name, Icon	Shown by a screen.
Layout	List: no size, arrival order. Slots: Slot Count slots, one stack each. Grid: Grid Size columns by rows; an item covers its Grid Footprint Size (width by height, 3 by 1 for a three-cell sword), one cell without one.
Allow Rotation	Grid only. Items may lie turned a quarter; adds try upright first.
Capacity Tag	Slots and Grid only. Each Capacity Bonus point owned adds a slot or grid row; empty keeps the size fixed (Capacity from items).
Rules	Limits judged over this container alone, such as a quiver filter (Rules).
Carried	Off for storage off the character (bank, stash): the belt, starting draw, a rack's Put Back, Consume Item, Get Item Count and Carry Rules ignore its items.
Takes New Items	Whether adds and pickups land here; off for a container players fill only by moving items in.
Access Tag	Tag the character must hold to move, use, drop, draw or consume the container's items (such as one a stash box grants). Empty is always in reach.
Opens Bags	A bag placed here opens its own container (Bags and Banks).

The config's Sort Order lists item kinds as Slot Tags, the order Request Sort lays a container out in.

A rule limits what goes in. Put it on a container's Rules to limit that container, or on the config's Carry Rules to limit everything carried. An item goes in only as far as every rule accepts: 15 arrows under a cap with room for 5 take 5.

Rule	Settings	Does
Weight Limit	Limit, Capacity Tag, Refuse Over Limit, Thresholds	Caps the load (each Weight fragment times its count), refusing the rest with `TooHeavy`. Refuse Over Limit off lets everything in; each threshold puts its Tag on the character at its Fraction of the limit.
Category Limit	Limits: Category, Max Units, Capacity Tag	Caps units per category, matched against Slot Tags with children. An item in no row passes; in several, the tightest applies.
Item Filter	Allowed Tags, Blocked Tags	Takes only items matching an Allowed Tag (empty takes any) and no Blocked Tag.
Belt Only	None	Takes an item only while a belt slot takes it, and more units only into the stacks on the belt, for a style with no inventory; pair it with the belt's Auto Populate from Inventory. On a container it limits that container alone, as on Simple's Belt list beside its Worn slots. Refuses with `Full` when the slots for it are held, `CategoryFull` at its copy limit, `NotAdmitted` when no slot takes it, and takes nothing new while the belt is switched off. A character with no player's belt, such as an AI, takes what the other rules allow.

Get Units That Fit, on the inventory and on a world item for its prompt, answers how many units an add would take and why it leaves the rest: Full, TooHeavy, CategoryFull, NotAdmitted, or NoAccess when only reach stopped it (every reason).

Status tags

A rule can put tags on the character while the contents earn them, as the Weight Limit's thresholds do in the Open World List and Party RPG configs. Give each tag an effect: a UPC Speed Modifier scale, or a sprint's or transition's Blocked Tags (Sprint and Speed).

A rule of your own

Inventory Rules and Combines in Blueprint builds a rule from a Blueprint class whose parent is UPCInventoryRule.

Capacity from items

An item with a Capacity Bonus fragment raises a capacity while owned (a quiver adds arrow space, a case upgrade a row). Each row names a Capacity Tag and an Amount per unit owned.

Details

Capacity Bonus

Bonuses

1 Array element

Index [ 0 ]

Capacity Tag

UPC.Inventory.Capacity.CaseRows

Amount

A case upgrade of your own. Owning it raises every capacity that reads UPC.Inventory.Capacity.CaseRows by 1, so the survival grid's case gets one more row. No demo item carries one.

A setting naming the tag reads the bonus in its own unit. With a bonus of 2 for MyGame.Capacity.Pack, a Grid container whose Capacity Tag is that tag gets 2 more rows, a Weight Limit naming it carries 2 more weight, and a Category Limit row naming it takes 2 more units. Get Capacity Bonus answers the total for a tag. The bonus counts in any container, the stash included. An upgrade inside the rows it enlarges cannot leave while they hold items, so keep it in the stash or in a container whose filter keeps it apart.

For example, a case upgrade kept in the stash adds one row to the case, and a herb sits in that row. Dropping the upgrade, storing it in a chest or putting it back on a rack is refused while the herb stays: Can Item Leave answers false with UPC.Inventory.Refused.CapacityInUse (the demo screens say Empty the extra slots first). Move the herb into the case's other rows and the upgrade can go. Game code that removes the upgrade asks nothing and moves nothing, so ask Can Item Leave first. A bag is judged with the bonus items inside it. For extra space whose items go with it when dropped, make the item a bag, as the survival grid's hip pouch is (Bags).

Caps per kind

A Category Limit carry rule caps each kind with no slots or weight (20 arrows, 4 consumables):

Details

InventoryConfig_MyCaps

Containers

1 Array element

Index [ 0 ]

Container

UPC.Inventory.Container.Satchel

Definition

Container_UPC_Satchel

Rules

Carry Rules

1 Array element

Index [ 0 ]

Category Limit

Limits

2 Array elements

Index [ 0 ]

Items on the belt and in hand

Setting	Does
Belt Space	Whether a belt item still takes its container spot. Keeps Its Place (default) keeps it. Frees Its Place gives it up while on the belt, so a belt clear or unequip that would leave no spot to return to is refused. Weight and category caps count the item either way. In a one-slot container the sword goes on the belt and the slot frees; a pickup fills it; taking the sword off the belt is then refused.
Equipped Space	The same for an item drawn or worn and off the belt.
Has Belt, Belt Slots	Whether the player has a belt under this config, and its slots' Slot Tags (Quick Bar).
Show Carried Items On Body	Hangs every carried Stowable item outside a bag on the body, not only the belt's (Equipment). Off by default; the survival grid turns it on.
Swap When Full	A pickup with no room puts down the item in the way, in hand or on a belt slot that takes the new one, for the new one (Pickups, Drops and Holders).

Combine Sets and timing

Setting	Does
Combine Sets	Combine Set assets this style uses, asked in order; empty means a drop never combines (Combines).
Equip At Once	An item equipped from the inventory reaches the hand instantly, no animation or wait. Off plays its draw animation or waits Draw Timing.
Draw Timing	Wait for an item with no draw animation (default 0.2 s; 0 is instant); an item's Equippable can override it.
Put Away At Once, Stow Timing	The same for putting an item away from the inventory.
Combine Result Place	Where a recipe's first result goes: Onto The Target (default), the place of the item combined onto; Onto The Source, the place of the item picked first; As Added, where a pickup would land. A place counts only when the combine uses up that item's whole stack and the result fits; otherwise the result goes where a pickup would.
Combine At Once	Every combine unit lands instantly, no wait or unit sounds. Needed for a screen that pauses the game, since a paused world runs no timers.

A belt press is not timed by these.

Debug it

Saving a config, a container definition or an item names each setup problem in the Message Log.
An add took fewer units than asked: print Get Units That Fit's Out Reason.

AdvancedRules in detail

A rule is one object every character using the asset shares, so it keeps no state of its own and answers from the inventory alone. Context names the inventory and the Scope judged: one container, or empty for everything carried, the scope Get Weight and Get Category Count read.
The inventory asks each rule once per add, over the contents as they stand, never between units. A rule letting in N units must let in any offer of N or fewer whole, since a pickup adds exactly the units its preview answered.
A move inside one container changes nothing a rule counts. A move between two judges the destination's rules, and the Carry Rules when it brings an item from storage into what the character carries.
A swap judges each side as if the other item were already gone (the context's Departing Item and Departing Units), so two items of equal weight trade places under a full Weight Limit.
Losing a capacity bonus removes nothing: items past a container's new end keep their places, the container takes new items only in free places inside its end, and a category over its cap takes no more until it is back under.
A held item moves where it is dropped: Request Move lets go of the belt slot or hand first, then places it, and turns the move down when letting go leaves it no place (a Plan Stow that keeps it in hand).
A rule reading something outside the inventory, such as a strength attribute, calls Refresh Limits on the inventory when that thing changes.
Is Container In Reach answers for a whole container, for a bank screen.
Saving flags a config where nothing takes new items, a Weight Limit of 0, a repeated or incomplete container row, a Slots or Grid container with no room and no bonus, an empty rule or Combine Sets entry, a recipe result no container lets in, and a threshold, category row or Capacity Bonus row with no tag.

MultiplayerWhat runs where

The server places every unit and reads the timing settings from the character's config; a request carries no choice of its own.
Rule status tags sit on the character as one gameplay effect that reaches every machine about half a round trip later and returns at the next change if removed.

C++C++

A rule is a UUPCInventoryRule subclass overriding GetUnitsAccepted_Implementation(const FUPCInventoryRuleContext&, const UUPCItemDefinition*, int32 Count, FGameplayTag& OutReason) and GetStatusTags_Implementation(const FUPCInventoryRuleContext&). Pass Context.Scope as it is to GetWeight and GetCategoryCount.
Rules are instanced objects on the config and definition assets, never on the inventory component. UUPCInventoryConfig::FindCombine returns the first recipe or combine that takes a pair.
UUPCInventoryConfig::FindContainer(Tag) returns a container's definition; UUPCInventoryComponent::GetContainerDefinition(Id) also answers for an open bag's container.