PhysicsPickupController.cs

using System.Collections.Generic;
using System.Linq;
using UnityEngine;

/// <summary>
/// Use Grab, Drop and ToggleGrab to grab/drop. A Holder Joint must be defined. It should be another GameObject that is parented to the camera that has a Rigidbody and ConfigurableJoint.
/// </summary>
public class PhysicsPickupController : MonoBehaviour {

    [SerializeField]
    ConfigurableJoint _holderJoint;

    [SerializeField]
    Rigidbody _holdingRigidbody;

    [SerializeField]
    float _raycastGrabDistance = 1;

    [SerializeField]
    float _raycastHoldDistance = 3f;

    [SerializeField]
    float _sphereCastRadius = .5f;

    [SerializeField]
    float _minHoldDistance = 1;

    [SerializeField]
    float _offsetHoldDistance = -1;

    [SerializeField]
    bool _freezeRotationOnPickup;

    Rigidbody _attachedRigidbody;

    #region Properties
    public float CurrentHoldDistance { get; private set; }

    public bool FreezeRotationOnPickup {
        get { return _freezeRotationOnPickup; }
        set { _freezeRotationOnPickup = value; }
    }

    public ConfigurableJoint HolderJoint {
        get { return _holderJoint; }
    }

    public Rigidbody HoldingRigidbody {
        get { return _holdingRigidbody; }
        set {
            if(HoldingRigidbody == value) return;

            if(HoldingRigidbody) IgnoreCollisions(HoldingRigidbody, false);
            else IgnoreCollisions(value, true);

            _holdingRigidbody = value;

            HolderJoint.connectedBody = value;
        }
    }

    public float MinHoldDistance {
        get { return _minHoldDistance; }
        set { _minHoldDistance = value; }
    }

    public float OffsetHoldDistance {
        get { return _offsetHoldDistance; }
        set { _offsetHoldDistance = value; }
    }

    public float RaycastGrabDistance {
        get { return _raycastGrabDistance; }
        set { _raycastGrabDistance = value; }
    }

    public float RaycastHoldDistance {
        get { return _raycastHoldDistance; }
        set { _raycastHoldDistance = value; }
    }

    public float SphereCastRadius {
        get { return _sphereCastRadius; }
        set { _sphereCastRadius = value; }
    }
    #endregion

    void Awake() {
        _attachedRigidbody = GetComponentInParent<Rigidbody>();
    }

    void Update() {
        UpdateHold();
    }

    public void Drop() {
        if(!HoldingRigidbody) return;

        if(FreezeRotationOnPickup)
            HoldingRigidbody.constraints &= ~RigidbodyConstraints.FreezeRotation;

        HoldingRigidbody = null;
    }

    public void Grab() {
        if(HoldingRigidbody) return;

        var ray = new Ray(transform.position, transform.forward);
        RaycastHit hit;

        if(Physics.Raycast(ray, out hit, RaycastHoldDistance, -1, QueryTriggerInteraction.Ignore)) {
            HoldingRigidbody = hit.rigidbody;

            if(FreezeRotationOnPickup)
                HoldingRigidbody.constraints |= RigidbodyConstraints.FreezeRotation;
        }
    }

    public void ToggleGrab() {
        if(HoldingRigidbody) Drop();
        else Grab();
    }

    void IgnoreCollisions(Rigidbody rigidbody, bool ignore) {
        if(rigidbody && _attachedRigidbody) {
            Collider holdingCollider = rigidbody.GetComponentInChildren<Collider>();

            foreach(var collider in _attachedRigidbody.GetComponentsInChildren<Collider>())
                Physics.IgnoreCollision(collider, holdingCollider, ignore);
        }
    }

    void UpdateHold() {
        if(!HoldingRigidbody) return;

        var ray = new Ray(transform.position, transform.forward);
        var raycastHits = Physics.SphereCastAll(ray, SphereCastRadius, RaycastHoldDistance, -1, QueryTriggerInteraction.Ignore);
        float maxHoldDistance = RaycastHoldDistance;

        raycastHits = raycastHits.OrderBy(s => s.distance).ToArray();

        for(int i = 0; i < raycastHits.Length; i++) {
            RaycastHit hit = raycastHits[i];

            if(!hit.collider.attachedRigidbody || (hit.collider.attachedRigidbody != HoldingRigidbody && hit.collider.attachedRigidbody != _attachedRigidbody)) {
                maxHoldDistance = Mathf.Min(hit.distance, RaycastHoldDistance);
                break;
            }
        }

        CurrentHoldDistance = Mathf.Max(MinHoldDistance, maxHoldDistance + OffsetHoldDistance);
        HolderJoint.transform.localPosition = new Vector3(0, 0, CurrentHoldDistance);
    }

    void OnDrawGizmos() {
        Gizmos.color = new Color(.2f, .6f, .2f);
        Gizmos.DrawRay(transform.position, transform.forward * RaycastGrabDistance);
    }
}