2D Rope Swinging in Unity

Reticle.cs

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

public class Reticle : MonoBehaviour {

    public GameObject prefab;
    GameObject sprite;
    LineRenderer line;

    Quaternion direction;
    Vector2 offscreen = new Vector2(999f, 999f);

    enum Mode { Controller, Mouse };
    Mode aimMode = Mode.Mouse;

    void Start () {
        direction = Quaternion.Euler(0, 0, 0);
        sprite = Instantiate(prefab, offscreen, Quaternion.identity);
        line = GetComponent<LineRenderer>();
    }

    void Update () {
        RenderReticle();

        float x = Input.GetAxis("RightHorizontal") * 10;
        float y = Input.GetAxis("RightVertical") * 10;
        float z;

        if (x != 0 || y != 0) {
            aimMode = Mode.Controller;
        }

        if (aimMode == Mode.Mouse) {
            Vector2 mouse = Camera.main.ScreenToWorldPoint(Input.mousePosition) - transform.position;
            z = Vector2.Angle(mouse, Vector2.up);
            x = mouse.x;
            if (x > 0) {
                z = 360 - z;
            }
            direction = Quaternion.Euler(0f, 0f, z);
        } else {

            // If there is no input, don't do anything.
            if (x == 0 && y == 0) { return; }

            // Translate the x and y coords to an angle from up.
            Vector3 vec = new Vector3(x, y, 0);
            z = Vector2.Angle(Vector2.up, vec);

            // I have no idea why this works, but it does.
            if (x > 0) {
                z += 180;
            } else {
                z = 180 - z;
            }

            direction = Quaternion.Slerp(direction, Quaternion.Euler(0f, 0f, z), 0.2f);
        }
    }

    // If there is a target, render the reticle there. Otherwise, render it offscreen.
    void RenderReticle() {
        Vector3 target = CurrentTarget();
        line.positionCount = 2;
        line.SetPosition(0, transform.position);

        if (target.x == 0 && target.y == 0) {
            sprite.transform.position = offscreen;
            line.SetPosition(1, transform.position + direction * (Vector3.up * 50));
        } else {
            sprite.transform.position = target;
            line.SetPosition(1, target);
        }
    }

    // Shoot a raycast toward direction and return the hit point
    public Vector2 CurrentTarget() {
        LayerMask mask = LayerMask.GetMask("Default");
        RaycastHit2D hit = Physics2D.CircleCast(transform.position + (Vector3.up * 1f),
                                                1.0f,
                                                direction * Vector3.up,
                                                Mathf.Infinity, mask);
        if (hit && hit.collider) {
            if (hit.collider.gameObject.GetComponent<Snappable>()) {
                return hit.collider.gameObject.transform.position;
            }
        }
        return hit.point;
    }
}

Rope.cs

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

public class Rope : MonoBehaviour {
    public GameObject source;
    public Vector3 target;
    public GameObject nodePrefab;

    GameObject lastNode;
    bool attached = true;

    // Has the rope reached it's target?
    bool inPlace = false;

    // Space between nodes
    float nodeSpace = 0.5f;

    LineRenderer line;
    List<GameObject> nodes = new List<GameObject>();

    void Start() {
        nodes.Clear();
        nodes.Add(gameObject);
        lastNode = gameObject;
        line = GetComponent<LineRenderer>();
    }

    // If our rope hits something on the way, attach to that instead
    void OnCollisionStay2D(Collision2D other) {
        Rigidbody2D rb = other.gameObject.GetComponent<Rigidbody2D>();
        if (!rb) rb = other.gameObject.GetComponentInParent<Rigidbody2D>();

        if (rb) {
            HingeJoint2D joint = gameObject.AddComponent<HingeJoint2D>();
            joint.connectedBody = rb;
            target = transform.position;
        }
    }

    void Update() {
        DrawRope();

        if (inPlace) return;

        if (transform.position == target) {
            inPlace = true;

            // Once we've reached our target, add nodes lining up back to the character
            while (Vector3.Distance(source.transform.position, lastNode.transform.position) > nodeSpace) {
                CreateNode();
            }

            // The connect the last node's hinge joint to whatever shot the web
            lastNode.GetComponent<HingeJoint2D>().connectedBody = source.GetComponent<Rigidbody2D>();

        } else {

            // Lerp toward the target
            transform.position = Vector3.MoveTowards(transform.position, target, 1.5f);
        }

    }

    // Use the LineRenderer to connect the dots
    void DrawRope() {
        line.positionCount = nodes.Count;

        // If we're attached, we need to add one more line segment to the user
        if (attached) {
            line.positionCount++;
            line.SetPosition(line.positionCount - 1, source.transform.position);
        }

        // Draw a line to each node's position
        int i = 0;
        for (; i < nodes.Count; i++) {
            line.SetPosition(i, nodes[i].transform.position);
        }
    }

    public void Detach() {
        Destroy(lastNode.GetComponent<HingeJoint2D>());
        attached = false;
        StartCoroutine(_destroy());
    }

    void CreateNode() {
        // Create a new node $nodeSpace distance toward the target
        Vector3 direction = source.transform.position - lastNode.transform.position;
        Vector3 position = (Vector3.Normalize(direction) * nodeSpace) + lastNode.transform.position;
        GameObject newNode = Instantiate(nodePrefab, position, Quaternion.identity);

        // Set it relative to rope
        newNode.transform.SetParent(transform);

        // Connect the lats node to this node
        lastNode.GetComponent<HingeJoint2D>().connectedBody = newNode.GetComponent<Rigidbody2D>();

        // And add the new node to the list
        lastNode = newNode;
        nodes.Add(newNode);
    }

    // Destroy a node every 0.1s starting from the source and going to the target
    IEnumerator _destroy() {
        yield return new WaitForSeconds(1.0f);
        for (int i = nodes.Count - 1; i >= 0; i--) {
            Destroy(nodes[i]);
            nodes.RemoveAt(i);
            yield return new WaitForSeconds(0.1f);
        }
    }
}

RopeShooter.cs

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

public class RopeShooter : MonoBehaviour {

    public GameObject ropePrefab;

    GameObject user;
    GameObject currentRope;
    bool shooting = false;

    void Start() {
        user = transform.parent.gameObject;
    }

    void Update() {
        bool activated = Mathf.Abs(Input.GetAxis("R2")) > 0 ||
            Input.GetMouseButton(0);

        if (shooting == false && activated) {
            Vector2 target = GetComponent<Reticle>().CurrentTarget();

            // If a Raycast2D doesn't hit anything, it returns point (0,0)
            if (target.x == 0 && target.y == 0) { return; }

            shooting = true;
            ShootRope(target);
        }

        if (shooting == true && !activated) {
            if (currentRope) {
                currentRope.GetComponent<Rope>().Detach();
            }
            shooting = false;
        }
    }

    public void ShootRope(Vector3 target) {
        GameObject rope = Instantiate(ropePrefab, transform.position, Quaternion.identity);
        Rope ropec = rope.GetComponent<Rope>();
        ropec.target = target;
        ropec.source = user;
        currentRope = rope;
    }

    public bool Attached() {
        return shooting;
    }
}

setup.txt

RopeShooter (Prefab)
  <RopeShooter RopePrefab=Rope>
  <Reticle Prefab=Reticle>
  
Rope (Prefab)
  <Rope NodePrefab=RopeNode>
  <CircleCollider2D>
  <Rigidbody2D>
  <HingeJoint2D>
  <LineRenderer>
  
RopeNode (Prefab)
  <CircleCollider2D>
  <Rigidbody2D>
  <HingeJoint2D>
  
Reticle (Prefab)
  <SpriteRenderer>

Demo at http://www-personal.umich.edu/~shreve/unity/ManSpider/