Add the Transport Truck

Complete Add Production and Research first. The Factory will produce a Truck for 150 Minerals. It carries four Soldiers, loads instantly, and unloads into open ground beside it.

1. Expose containment for authoring

The containment runtime provides container and passenger data, but these two types currently have no Add Component entries. Add two small authoring components to the game’s C++ module so their data can be configured on your Blueprints.

Close the editor. In Source/SeinDemo/SeinDemo.Build.cs, add SeinARTSCoreEntity to PublicDependencyModuleNames alongside the existing Core, CoreUObject, and Engine dependencies.

Create Source/SeinDemo/DemoTransportComponents.h with:

#pragma once

#include "CoreMinimal.h"
#include "Authoring/SeinEntityComponent.h"
#include "Components/SeinContainmentData.h"
#include "Components/SeinContainmentMemberData.h"
#include "DemoTransportComponents.generated.h"

/** Authors the container data used by Enter Container and Exit Container. */
UCLASS(NotBlueprintable, ClassGroup = (SeinARTS),
    meta = (BlueprintSpawnableComponent))
class SEINDEMO_API UDemoTransportComponent : public USeinEntityComponent
{
    GENERATED_BODY()
public:
    /** Capacity, accepted passengers, and behavior when this transport dies. */
    UPROPERTY(EditAnywhere, Category = "SeinARTS",
        meta = (ShowOnlyInnerProperties))
    FSeinContainmentData Transport;

    virtual const UScriptStruct* GetPayloadStruct() const override
    {
        return FSeinContainmentData::StaticStruct();
    }

    virtual bool WritePayload(FInstancedStruct& Out) const override
    {
        Out.InitializeAs<FSeinContainmentData>(Transport);
        return true;
    }
};

/** Authors passenger size; the simulation maintains its container reference. */
UCLASS(NotBlueprintable, ClassGroup = (SeinARTS),
    meta = (BlueprintSpawnableComponent))
class SEINDEMO_API UDemoPassengerComponent : public USeinEntityComponent
{
    GENERATED_BODY()
public:
    /** Space occupied by this entity when it enters a transport. */
    UPROPERTY(EditAnywhere, Category = "SeinARTS",
        meta = (ShowOnlyInnerProperties))
    FSeinContainmentMemberData Passenger;

    virtual const UScriptStruct* GetPayloadStruct() const override
    {
        return FSeinContainmentMemberData::StaticStruct();
    }

    virtual bool WritePayload(FInstancedStruct& Out) const override
    {
        Out.InitializeAs<FSeinContainmentMemberData>(Passenger);
        return true;
    }
};

Create Source/SeinDemo/DemoTransportComponents.cpp containing:

#include "DemoTransportComponents.h"

Regenerate the project’s Visual Studio files, build Development Editor / Win64, then reopen the project. Demo Transport and Demo Passenger should appear in Add Component. Their parent handles baking the authored values for simulation; neither component needs a tick or event graph.

2. Create the Truck

Create a Generic SeinARTS Entity named SU_Truck. Set its identity Display Name to Truck.

Add the following components:

Component	Configuration
Static Mesh	Engine Cube; relative Location (0, 0, 75), Scale (4, 2, 1.5)
Sein Navigation	Default
Sein Vision	Default
Sein Extents	Box: Forward half extent 200, Right half extent 100, Height 150; Collision enabled
Sein Movement	Top Speed 600; Movement Class SeinBasicUnitMovement
SC_DemoHealthComponent	Health and MaxHealth 300
Sein Abilities	Grant SA_Move; map RightClick + Target.Ground to its tag
Sein Producible	Build Time 8
Demo Transport	Total Capacity 4

On Demo Transport, edit Accepted Entity Query to require the Soldier’s identity tag, SeinARTS.Unit.Soldier. Set Movement Ability to SA_Move. Compile and save.

On SU_Soldier, add Demo Passenger. Compile and save.

3. Produce Trucks

Create a Generic Ability named SA_Produce_Truck. Set Ability Name Build Truck, Dispatch Mode Single, Cost Timing Production Queue, and Resource Cost to 150 Minerals. Block it with SeinARTS.State.UnderConstruction.

Use the same queue-capacity Can Activate function as Train Soldier. On Activate, Enqueue Production with SU_Truck, then End Ability.

Grant it to the Factory. Its existing rally-point ability also works for Trucks. Compile and save.

4. Embark a Soldier

Create a Generic Ability named SA_Embark, Ability Name Embark, Target Type Entity, Max Range 350, and Out Of Range Behavior Auto Move Then.

Set Cancel Abilities With Tag to SeinARTS.Ability so embarking can replace movement, attack, or harvesting.

Set Valid Target Tags to a query requiring SeinARTS.Unit.Truck. The ability checks these conditions on Activate:

1. Owner Entity and Target Entity are alive.
2. Get Entity Owner returns the same player ID for both.
3. Is Contained on Owner Entity is false.
4. Can Accept Entity, with Container = Target Entity and Entity = Owner Entity, is true.

If any check fails, End Ability. Otherwise call Enter Container with Entity = Owner Entity and Container = Target Entity, then End Ability. The containment operation checks capacity again, so simultaneous loading cannot exceed four seats.

Grant SA_Embark to the Soldier. Add a Default Commands entry requiring RightClick and Target.Friendly, Ability Tag SeinARTS.Ability.Embark, Priority 10. The target-tag check rejects friendly entities that are not Trucks.

5. Keep passengers inactive and hidden

Override Can Activate on SA_Move, SA_Attack, SA_Harvest, SA_Place_Barracks, and SA_Place_Factory to return NOT Is Contained(Owner Entity). If a graph already contains an eligibility rule, AND this condition with it. This also applies to movement orders issued while a Soldier remains selected after loading.

In SU_Soldier’s actor Event Graph, use Event Tick only for presentation:

1. Call Get Entity Handle on self.
2. Call Is Contained with that handle.
3. Set the skeletal mesh’s Visibility to the inverse result.
4. Set its Collision Enabled to No Collision while contained and Query Only when outside.

The containment system removes hidden passengers from spatial queries and vision contribution. Hiding the mesh separately makes the visual representation agree. Keep this graph free of simulation writes.

Compile and save.

6. Unload passengers

Create a Generic Ability named SA_Disembark, Ability Name Unload. Grant it to the Truck.

On Activate, copy Get Occupants(Owner Entity) into a local entity-handle array. Iterate that copy with a For Each Loop; the live occupant array changes when passengers leave.

For each occupant at Array Index i:

1. Make a Fixed Vector local exit offset (-300, -150 + 100 * i, 0).
2. Get the Truck’s Fixed Transform with Get Entity Transform. Use Fixed Transform Transform Position to convert the local offset to a world position.
3. Call Is Location Reachable from the Truck’s current location to that point. If false, leave this passenger aboard.
4. If true, call Exit Container, Entity = the occupant, Exit Location = the calculated world point.

Call End Ability from the loop’s Completed output. Keep the four exit positions clear of other units and obstacles when testing. This simple reachability check does not reserve space against other units; the collision system handles local separation after a successful exit.

7. Show occupancy

Add a Text Block OccupancyText to the HUD SelectionPanel. In RefreshHUD, call Get Containment Data with the primary model’s Entity. On success, display Current Load / Total Capacity. Otherwise collapse the text block.

8. Test transport

Produce a Truck, then move it onto open floor. Select four Soldiers and right-click it. Check occupancy reaches 4 / 4, their meshes disappear, and their individual movement orders cannot move them while aboard.

Move the Truck, select it, and click Unload. The Soldiers should appear behind it and regain movement and harvesting. Try loading a fifth Soldier into a full Truck; it should remain outside. In the two-player test later, destroy a loaded Truck and verify its passengers are ejected under the authored death policy.

Checkpoint

• The Factory produces the second mobile unit type.
• Capacity and accepted passenger types are authored on the Truck.
• Embark and Unload call the framework’s containment operations.
• Passengers retain ownership and cannot act while contained.

Continue with Add Fog and a Minimap.