How do you implement object manipulation (e.g., grabbing, throwing) in VR?

Implementing object manipulation in VR involves handling input detection, physics, and spatial tracking to create believable interactions. The core process typically starts with detecting when a user intends to grab an object, often through controller button presses or hand-tracking gestures like pinching. In engines like Unity or Unreal, you’d attach colliders to interactable objects and use raycasting or proximity checks to determine when a controller or virtual hand is near an object. For example, in Unity’s XR Interaction Toolkit, an object tagged as “XR Grab Interactable” can be linked to a controller’s “XR Direct Interactor” component, which handles grabbing logic. When the user triggers a grab action, the object’s parent is set to the controller, making it follow its movement. Physics-based grabbing might instead apply forces or joints to simulate weight, depending on the object’s rigidbody settings.

Throwing requires calculating the object’s velocity when released. This is done by tracking the controller’s movement over a few frames before release and transferring that velocity to the object. In Unity, the “XR Grab Interactable” component includes a “Throw Velocity Scale” parameter to adjust how forcefully objects are thrown. For manual implementation, you might store the controller’s positional data over time, compute the delta, and apply it to the object’s rigidbody. Physics materials can be used to tweach friction or bounciness for realistic collisions. In Unreal, the “Physics Handle” component can attach and release objects while preserving momentum. For hand tracking (like Meta Quest), gesture recognition (e.g., detecting an open palm vs. a fist) replaces button presses, requiring additional logic to map hand states to grab/release events.

User feedback is critical for immersion. Visual cues, like highlighting objects when hovered or animating a hand model to close around a grabbed object, reinforce interaction clarity. Haptic feedback—short vibrations on grab/release—can be triggered via APIs like Unity’s InputSystem.SendHapticImpulse or Unreal’s Play Haptic Effect node. For example, a light rumble when grabbing a metal object versus a softer pulse for a foam ball adds tactile realism. Testing is essential: ensure objects don’t clip through surfaces, velocities feel natural, and interactions remain responsive. Tools like Unity’s XR Interaction Debugger or Unreal’s VR Template can help identify issues like misaligned colliders or incorrect input mappings.