Physical Inventory System

Unreal Engine 5 Tutorial

0. Migration (if necessary).

Migration (if necessary).

This asset is provided as a sample project. If you need to integrate this asset into your project, follow these steps:

Open the backpack project and select the Content > 3dInventory folder. Right-click and select Migrate > Your Project > Content folder.

After successful migration, you can close this project and immediately open your own.

For successful operation, you need to create additional collision channels: Project Setting > Collision and create a new

Object Channels > BackpackObj = Ignore

Trace Channels > Backpack = Ignore

For the Outline Effect to work, ensure that:

Project Setting > Rendering > Custom Depth-Stencil Pass = Enabled with Stencil

That's all you need to do to proceed with your project.

Backpack Setup Guide

1. Getting Started

Choose the correct backpack component:

BPC_Backpack_SM — if you use a Static Mesh.
BPC_Backpack_SK — if you use a Skeletal Mesh.

Create a duplicate of the chosen blueprint and open it.

Replace the default SM_Backpack or SK_Backpack with your own backpack mesh inside the blueprint.
Position the mesh the way you want.

2. Material Setup

Open your backpack mesh → open its materials.

For each material:

Add the MF_Backpack function.
Connect it to OpacityMask (or Opacity). If both are inactive, select Blend Mode = Masked in the material settings.
If needed, plug your alpha mask texture into the Alpha input.

3. Adjusting Blueprint Components

Return to your backpack blueprint.

SpawnPoint / DropPoint

Adjust their positions:

SpawnPoint — where the item appears when picked up.
DropPoint — where the item is dropped.

Important: move the component, not the pointer selected in the viewport.

BP_CameraBackpack

Rotate and position the camera so it looks directly at the center of your backpack working area.

Slicer

Move the Slicer so your backpack opening looks correct.

4. Setting Collision Boundaries

You can set boundaries in two ways:

✅ Recommended Method: Custom Mesh Boundaries

Create custom collision meshes that describe your backpack shape:

Top Lid — detects when an object tries to exit the backpack area.
- Collision: Block All
Main Volume — ensures the item is inside the backpack.
- Collision: Outside Only
Inner Walls — main space used for physical movement inside the backpack.
- Collision: Block All

If needed, duplicate boundaries multiple times to prevent pushing objects inside from the outside (example OverlapExternal and BlockExternal).

➤ Alternative Method (used in this example): Shapes / Mesh Components

You can use:

Box Collision components, or
Mesh components (recommended if you want debug visualization).

5. Skeletal Mesh Users

Before editing BP_Backpack_SK:

Open Construction Script and disconnect the bone-space transformation node.
This prevents bone transforms from interfering with boundary placement.

After finishing boundaries, reconnect the node.

6. Example Boundary Placement

Here are some screenshots showing:

how to place boundaries,
how to add the internal overlap shape,
how to define the main collision walls.

Use as many shapes as needed for precise collision.

And we add an overlay that will determine that our object is now in the backpack.

This is how I did it for BP_Backpack_SM (Static Mesh type), you can do the same for Skeletal Mesh (basic setup)

7. Collision Settings

Set the following:

Blocking Walls (green + transparent)

Collision: Block All (Custom)
BackpackObj = Block
Use CCD: True
Place under SBlock (Scene Component)

Top Lid + Detect Area (red)

Collision: Overlap All (Custom)
BackpackObj = Overlap
Place under SOverlap (Scene Component)

General settings for overlay and block

Set Visibility = Ignore (for traces)
Backpack = Ignore
Pawn = Ignore

8. Construction Script Variables

Inside your backpack blueprint set:

Detect → the inner overlap zone.
Backpack → your Static or Skeletal Mesh.
Parent → Construction Script parent execution.

These variables already exist in the parent class, just set values to them.

Skeletal Mesh Only

Use Attach Component to Component to bind all backpack logic to the correct bone (usually spine_05).

9. Character Setup

Open your BP_Character.

Setup your Character Skeletal Mesh

Disable movement during inventory

Add a Branch to all movement events (jump, crouch, run, walk, look).
This ensures the character cannot move while the backpack UI is active.

Add Interface

Add BPI_3dInventory to your character.

Copy Main Functions

Open the example BP_Character and copy the “Main Backpack Functions” block into your character.
Create missing variables (highlighted in blue) and set default values.

You can remove:

Grab Phys Objects block
Client Only: Interaction Trace if you use your own trace system
(just ensure Interacted Actor is updated correctly)

10. Adding the Backpack to the Character

Create a Child Actor Component and assign:

BP_Camera_SM (or Skeletal version)

Position the backpack where you want it to appear.

Construction Script

Copy the example logic:

Set As BP_Backpack variable.
For skeletal backpacks, attach the mesh to the correct bone in your character’s skeleton.

11. Optional: Outline Effect

If you want to use the outline system:

Add a Post Process Component
Configure it as shown in the example screenshot.

12. Setting Up Items

Create a child class of BP_Item (or use the example in the map).
Assign a Static Mesh to Cube.

Set collision on those objects:
Backpack = Ignore
BackpackObj = Block

During backpack use:

Item collision switches to BackpackObj
When dropped → back to PhysicsBody

Occlusion Mask

If you want certain world objects to remain visible through the backpack camera:

Add MF_OcclusionMask to their materials (works even in translucent mode)

13. Backpack Camera Controls

Included debug controls:

RMB — move camera
RMB + MMB — rotate camera

Disable before release by setting:
BP_BackpackCamera > BlockDebugControl = true

14. Support

If you encounter issues or bugs, please email me before leaving a negative review — I’ll fix everything quickly.
Good reviews motivate me to continue improving the project!
This project took a lot of time and energy to create.
Thank you for supporting it with a positive rating!
Submit bugs here:
Bug Report Form
or write me: myalreadyday@gmail.com

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