BPC_PhysicsDragSystem — Physics Drag System

Parent Class: ActorComponent Category: Interaction Target UE Version: 5.5–5.7 Build Phase: 2 — Interaction

1. Overview

BPC_PhysicsDragSystem allows the player to grab and physically drag rigid-body objects in the world. Supports grab-at-distance, hold-to-grab with physics constraints, object rotation, and throw mechanics. Integrates with the interaction detector for grab targeting.

2. Enums

`E_DragMode`

Value	Description
`PhysicsConstraint`	Attaches object via physics constraint to player hand
`Kinematic`	Sets object to kinematic and parents to hand
`Magnetic`	Objects smoothly lerp toward grab point

3. Variables

Name	Type	Description
`DragMode`	`E_DragMode`	Current drag physics mode
`GrabbedObject`	`AActor*`	Currently held actor
`ConstraintComp`	`UPhysicsConstraintComponent*`	Physics constraint for held object
`GrabDistance`	`float`	Max distance to grab (cm)
`HoldDistance`	`float`	Distance object is held from camera
`ThrowForce`	`float`	Impulse applied on release
`RotationSpeed`	`float`	Degrees/sec for object rotation input
`bCanThrow`	`bool`	Object can be thrown on release
`bIsGrabbing`	`bool`	Currently holding an object

4. Functions

Function	Description
`GrabObject`	Attempts to grab targeted physics object. Returns bool.
`ReleaseObject`	Releases held object, applies throw force if bCanThrow.
`RotateObject`	Rotates held object by input axis values
`SetHoldDistance`	Adjusts distance of held object from camera
`GetGrabbedObject`	Returns currently held actor (or null)
`IsGrabbing`	Returns `bIsGrabbing`

5. Event Dispatchers

Dispatcher	Payload	Description
`OnObjectGrabbed`	`AActor* GrabbedObject`	Object successfully grabbed
`OnObjectReleased`	`AActor* ReleasedObject`, `bool bWasThrown`	Object released
`OnGrabFailed`	`FText FailReason`	Grab attempt failed

6. Blueprint Flow

GrabObject:
  → Get targeted object from InteractionDetector
  → Check if object has physics simulation enabled
  → If DragMode == PhysicsConstraint:
      → Create physics constraint between hand socket and object
      → Set constraint limits (linear + angular)
  → If DragMode == Kinematic:
      → Set object simulated physics to false
      → Attach to hand socket
  → Set bIsGrabbing = true
  → Broadcast OnObjectGrabbed

ReleaseObject:
  → If bCanThrow → Apply forward impulse * ThrowForce
  → Destroy constraint / detach
  → Re-enable physics on object
  → Set bIsGrabbing = false
  → Broadcast OnObjectReleased

7. Dependencies & Communication

System	Relationship
`BPC_InteractionDetector`	Provides grab target via focus
`BPC_CameraStateLayer`	Camera direction for throw vector
`BPC_MovementStateSystem`	Speed modifier while carrying objects

8. Reuse Notes

Physics drag uses UE5 physics constraint system for realistic object handling
Objects must have Simulate Physics = true and Mass configured

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