AIPath.cs for development of A* Pathfinding Project 3.2

//#define DEBUG
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using Pathfinding;

/** AI for following paths.
 * This AI is the default movement script which comes with the A* Pathfinding Project.
 * It is in no way required by the rest of the system, so feel free to write your own. But I hope this script will make it easier
 * to set up movement for the characters in your game. This script is not written for high performance, so I do not recommend using it for large groups of units.
 * \n
 * \n
 * This script will try to follow a target transform, in regular intervals, the path to that target will be recalculated.
 * It will on FixedUpdate try to move towards the next point in the path.
 * However it will only move in the forward direction, but it will rotate around it's Y-axis
 * to make it reach the target.
 *
 * \section variables Quick overview of the variables
 * In the inspector in Unity, you will see a bunch of variables. You can view detailed information further down, but here's a quick overview.\n
 * The #repathRate determines how often it will search for new paths, if you have fast moving targets, you might want to set it to a lower value.\n
 * The #target variable is where the AI will try to move, it can be a point on the ground where the player has clicked in an RTS for example.
 * Or it can be the player object in a zombie game.\n
 * The speed is self-explanatory, so is turningSpeed, however #slowdownDistance might require some explanation.
 * It is the approximate distance from the target where the AI will start to slow down. Note that this doesn't only affect the end point of the path
 * but also any intermediate points, so be sure to set #forwardLook and #pickNextWaypointDist to a higher value than this.\n
 * #pickNextWaypointDist is simply determines within what range it will switch to target the next waypoint in the path.\n
 * #forwardLook will try to calculate an interpolated target point on the current segment in the path so that it has a distance of #forwardLook from the AI\n
 * Below is an image illustrating several variables as well as some internal ones, but which are relevant for understanding how it works.
 * Note that the #forwardLook range will not match up exactly with the target point practically, even though that's the goal.
 * \shadowimage{aipath_variables.png}
 * This script has many movement fallbacks.
 * If it finds a NavmeshController, it will use that, otherwise it will look for a character controller, then for a rigidbody and if it hasn't been able to find any
 * it will use Transform.Translate which is guaranteed to always work.
 */
[RequireComponent(typeof(Seeker))]
public class AIPath : MonoBehaviour {

    /** Determines how often it will search for new paths.
     * If you have fast moving targets or AIs, you might want to set it to a lower value.
     * The value is in seconds between path requests.
     */
    public float repathRate = 0.5F;

    /** Target to move towards.
     * The AI will try to follow/move towards this target.
     * It can be a point on the ground where the player has clicked in an RTS for example, or it can be the player object in a zombie game.
     */
    public Transform target;

    /** Enables or disables searching for paths.
     * Setting this to false does not stop any active path requests from being calculated or stop it from continuing to follow the current path.
     * \see #canMove
     */
    public bool canSearch = true;

    /** Enables or disables movement.
      * \see #canSearch */
    public bool canMove = true;

    /** Maximum velocity.
     * This is the maximum speed in world units per second.
     */
    public float speed = 3;

    /** Rotation speed.
     * Rotation is calculated using Quaternion.SLerp. This variable represents the damping, the higher, the faster it will be able to rotate.
     */
    public float turningSpeed = 5;

    /** Distance from the target point where the AI will start to slow down.
     * Note that this doesn't only affect the end point of the path
     * but also any intermediate points, so be sure to set #forwardLook and #pickNextWaypointDist to a higher value than this
     */
    public float slowdownDistance = 0.6F;

    /** Determines within what range it will switch to target the next waypoint in the path */
    public float pickNextWaypointDist = 2;

    /** Target point is Interpolated on the current segment in the path so that it has a distance of #forwardLook from the AI.
      * See the detailed description of AIPath for an illustrative image */
    public float forwardLook = 1;

    /** Distance to the end point to consider the end of path to be reached.
     * When this has been reached, the AI will not move anymore until the target changes and OnTargetReached will be called.
     */
    public float endReachedDistance = 0.2F;

    /** Do a closest point on path check when receiving path callback.
     * Usually the AI has moved a bit between requesting the path, and getting it back, and there is usually a small gap between the AI
     * and the closest node.
     * If this option is enabled, it will simulate, when the path callback is received, movement between the closest node and the current
     * AI position. This helps to reduce the moments when the AI just get a new path back, and thinks it ought to move backwards to the start of the new path
     * even though it really should just proceed forward.
     */
    public bool closestOnPathCheck = true;

    public bool recyclePaths = true;

    protected float minMoveScale = 0.05F;

    /** Cached Seeker component */
    protected Seeker seeker;

    /** Cached Transform component */
    protected Transform tr;

    /** Time when the last path request was sent */
    private float lastRepath = -9999;

    /** Current path which is followed */
    protected Path path;

    /** Cached CharacterController component */
    protected CharacterController controller;

    /** Cached NavmeshController component */
    protected NavmeshController navController;

    /** Cached Rigidbody component */
    protected Rigidbody rigid;

    /** Current index in the path which is current target */
    protected int currentWaypointIndex = 0;

    /** Holds if the end-of-path is reached
     * \see TargetReached */
    protected bool targetReached = false;

    /** Only when the previous path has been returned should be search for a new path */
    protected bool canSearchAgain = true;

    /** Returns if the end-of-path has been reached
     * \see targetReached */
    public bool TargetReached {
        get {
            return targetReached;
        }
    }

    // Use this for initialization
    void Awake () {
        seeker = GetComponent<Seeker>();

        //This is a simple optimization, cache the transform component lookup
        tr = transform;

        //Make sure we receive callbacks when paths complete
        seeker.pathCallback += OnPathComplete;

        //Cache some other components (not all are necessarily there)
        controller = GetComponent<CharacterController>();
        navController = GetComponent<NavmeshController>();
        rigid = rigidbody;
    }

    public void Start () {
        StartCoroutine (RepeatTrySearchPath ());
    }

    public IEnumerator RepeatTrySearchPath () {
        while (true) {
            TrySearchPath ();
            yield return new WaitForSeconds (repathRate);
        }
    }

    public void TrySearchPath () {
        if (Time.time - lastRepath >= repathRate && canSearchAgain && canSearch) {
            SearchPath ();
        } else {
            StartCoroutine (WaitForRepath ());
        }
    }

    private bool waitingForRepath = false;
    protected IEnumerator WaitForRepath () {
        if (waitingForRepath) yield break; //A coroutine is already running

        waitingForRepath = true;
        //Wait until it is predicted that the AI should search for a path again
        yield return new WaitForSeconds (repathRate - (Time.time-lastRepath));

        waitingForRepath = false;
        //Try to search for a path again
        TrySearchPath ();
    }

    public void SearchPath () {

        if (target == null) { Debug.LogError ("Target is null, aborting all search"); return; }

        lastRepath = Time.time;
        //This is where we should search to
        Vector3 targetPoint = target.position;

        canSearchAgain = false;

        //Alternative way of requesting the path
        //Path p = PathPool<Path>.GetPath().Setup(GetFeetPosition(),targetPoint,null);
        //seeker.StartPath (p);

        //We should search from the current position
        seeker.StartPath (GetFeetPosition(), targetPoint);
    }

    public virtual void OnTargetReached () {
        //End of path has been reached
        //If you want custom logic for when the AI has reached it's destination
        //add it here
        //You can also create a new script which inherits from this one
        //and override the function in that script
    }

    public void OnDestroy () {
        if (path != null) path.Release (this);
    }

    /** Called when a requested path has finished calculation.
      * A path is first requested by #SearchPath(), it is then calculated, probably in the same or the next frame.
      * Finally it is returned to the seeker which forwards it to this function.\n
      */
    public void OnPathComplete (Path _p) {
        ABPath p = _p as ABPath;
        if (p == null) throw new System.Exception ("This function only handles ABPaths, do not use special path types");

        //Release the previous path
        if (path != null) path.Release (this);

        //Claim the new path
        p.Claim (this);

        //Replace the old path
        path = p;

        //Reset some variables
        currentWaypointIndex = 0;
        targetReached = false;
        canSearchAgain = true;

        //The next row can be used to find out if the path could be found or not
        //If it couldn't (error == true), then a message has probably been logged to the console
        //however it can also be got using p.errorLog
        //if (p.error)

        if (closestOnPathCheck) {
            Vector3 p1 = p.startPoint;
            Vector3 p2 = GetFeetPosition ();
            float magn = Vector3.Distance (p1,p2);
            Vector3 dir = p2-p1;
            dir /= magn;
            int steps = (int)(magn/pickNextWaypointDist);
            for (int i=0;i<steps;i++) {
                CalculateVelocity (p1);
                p1 += dir;
            }
#if DEBUG
            Debug.DrawLine (p1,p2,Color.red,1);
#endif
        }
    }

    public virtual Vector3 GetFeetPosition () {
        if (controller != null)
            return tr.position - Vector3.up*controller.height*0.5F;

        return tr.position;
    }

    public void Update () {

        if (!canMove) { return; }

        Vector3 dir = CalculateVelocity (GetFeetPosition());

        //Rotate towards targetDirection (filled in by CalculateVelocity)
        if (targetDirection != Vector3.zero) {
            RotateTowards (targetDirection);
        }

        if (navController != null) {
            navController.SimpleMove (GetFeetPosition(),dir);
        } else if (controller != null) {
            controller.SimpleMove (dir);
        } else if (rigid != null) {
            rigid.AddForce (dir);
        } else {
            transform.Translate (dir*Time.deltaTime, Space.World);
        }
    }

    /** Point to where the AI is heading.
      * Filled in by #CalculateVelocity */
    protected Vector3 targetPoint;
    /** Relative direction to where the AI is heading.
     * Filled in by #CalculateVelocity */
    protected Vector3 targetDirection;

    protected float XZSqrMagnitude (Vector3 a, Vector3 b) {
        float dx = b.x-a.x;
        float dz = b.z-a.z;
        return dx*dx + dz*dz;
    }

    /** Calculates desired velocity.
     * Finds the target path segment and returns the forward direction, scaled with speed.
     * A whole bunch of restrictions on the velocity is applied to make sure it doesn't overshoot, does not look too far ahead,
     * and slows down when close to the target.
     * /see speed
     * /see endReachedDistance
     * /see slowdownDistance
     * /see CalculateTargetPoint
     * /see targetPoint
     * /see targetDirection
     * /see currentWaypointIndex
     */
    protected Vector3 CalculateVelocity (Vector3 currentPosition) {
        if (path == null || path.vectorPath == null || path.vectorPath.Count == 0) return Vector3.zero;

        List<Vector3> vPath = path.vectorPath;
        //Vector3 currentPosition = GetFeetPosition();

        if (vPath.Count == 1) {
            vPath.Insert (0,currentPosition);
        }

        if (currentWaypointIndex >= vPath.Count) { currentWaypointIndex = vPath.Count-1; }

        if (currentWaypointIndex <= 1) currentWaypointIndex = 1;

        while (true) {
            if (currentWaypointIndex < vPath.Count-1) {
                //There is a "next path segment"
                float dist = XZSqrMagnitude (vPath[currentWaypointIndex], currentPosition);
                    //Mathfx.DistancePointSegmentStrict (vPath[currentWaypointIndex+1],vPath[currentWaypointIndex+2],currentPosition);
                if (dist < pickNextWaypointDist*pickNextWaypointDist) {
                    currentWaypointIndex++;
                } else {
                    break;
                }
            } else {
                break;
            }
        }

        Vector3 dir = vPath[currentWaypointIndex] - vPath[currentWaypointIndex-1];
        Vector3 targetPoint = CalculateTargetPoint (currentPosition,vPath[currentWaypointIndex-1] , vPath[currentWaypointIndex]);
            //vPath[currentWaypointIndex] + Vector3.ClampMagnitude (dir,forwardLook);



        dir = targetPoint-currentPosition;
        dir.y = 0;
        float targetDist = dir.magnitude;

        float slowdown = Mathf.Clamp01 (targetDist / slowdownDistance);

        this.targetDirection = dir;
        this.targetPoint = targetPoint;

        if (currentWaypointIndex == vPath.Count-1 && targetDist <= endReachedDistance) {
            if (!targetReached) { targetReached = true; OnTargetReached (); }

            //Send a move request, this ensures gravity is applied
            return Vector3.zero;
        }

        Vector3 forward = tr.forward;
        float dot = Vector3.Dot (dir.normalized,forward);
        float sp = speed * Mathf.Max (dot,minMoveScale) * slowdown;

#if DEBUG
        Debug.DrawLine (vPath[currentWaypointIndex-1] , vPath[currentWaypointIndex],Color.black);
        Debug.DrawLine (GetFeetPosition(),targetPoint,Color.red);
        Debug.DrawRay (targetPoint,Vector3.up, Color.red);
        Debug.DrawRay (GetFeetPosition(),dir,Color.yellow);
        Debug.DrawRay (GetFeetPosition(),forward*sp,Color.cyan);
#endif

        if (Time.deltaTime  > 0) {
            sp = Mathf.Clamp (sp,0,targetDist/(Time.deltaTime*2));
        }
        return forward*sp;
    }

    /** Rotates in the specified direction.
     * Rotates around the Y-axis.
     * \see turningSpeed
     */
    protected virtual void RotateTowards (Vector3 dir) {
        Quaternion rot = tr.rotation;
        Quaternion target = Quaternion.LookRotation (dir);

        rot = Quaternion.Slerp (rot,target,turningSpeed*Time.fixedDeltaTime);
        Vector3 euler = rot.eulerAngles;
        euler.z = 0;
        euler.x = 0;
        rot = Quaternion.Euler (euler);

        tr.rotation = rot;
    }

    /** Calculates target point from the current line segment.
     * \param p Current position
     * \param a Line segment start
     * \param b Line segment end
     * The returned point will lie somewhere on the line segment.
     * \see #forwardLook
     * \todo This function uses .magnitude quite a lot, can it be optimized?
     */
    protected Vector3 CalculateTargetPoint (Vector3 p, Vector3 a, Vector3 b) {
        a.y = p.y;
        b.y = p.y;

        float magn = (a-b).magnitude;
        if (magn == 0) return a;

        float closest = Mathfx.Clamp01 (Mathfx.NearestPointFactor (a, b, p));
        Vector3 point = (b-a)*closest + a;
        float distance = (point-p).magnitude;

        float lookAhead = Mathf.Clamp (forwardLook - distance, 0.0F, forwardLook);

        float offset = lookAhead / magn;
        offset = Mathf.Clamp (offset+closest,0.0F,1.0F);
        return (b-a)*offset + a;
    }
}