Moving Object Script

Checked with version: 5


Difficulty: Intermediate

This is part 6 of 14 of the 2D Roguelike tutorial in which we write the MovingObject script which the Player and Enemy scripts will inherit from to share movement code.

Moving Object Script

Intermediate 2D Roguelike tutorial



Code snippet

using UnityEngine;
using System.Collections;

    //The abstract keyword enables you to create classes and class members that are incomplete and must be implemented in a derived class.
    public abstract class MovingObject : MonoBehaviour
        public float moveTime = 0.1f;           //Time it will take object to move, in seconds.
        public LayerMask blockingLayer;         //Layer on which collision will be checked.
        private BoxCollider2D boxCollider;      //The BoxCollider2D component attached to this object.
        private Rigidbody2D rb2D;               //The Rigidbody2D component attached to this object.
        private float inverseMoveTime;          //Used to make movement more efficient.
        //Protected, virtual functions can be overridden by inheriting classes.
        protected virtual void Start ()
            //Get a component reference to this object's BoxCollider2D
            boxCollider = GetComponent <BoxCollider2D> ();
            //Get a component reference to this object's Rigidbody2D
            rb2D = GetComponent <Rigidbody2D> ();
            //By storing the reciprocal of the move time we can use it by multiplying instead of dividing, this is more efficient.
            inverseMoveTime = 1f / moveTime;
        //Move returns true if it is able to move and false if not. 
        //Move takes parameters for x direction, y direction and a RaycastHit2D to check collision.
        protected bool Move (int xDir, int yDir, out RaycastHit2D hit)
            //Store start position to move from, based on objects current transform position.
            Vector2 start = transform.position;
            // Calculate end position based on the direction parameters passed in when calling Move.
            Vector2 end = start + new Vector2 (xDir, yDir);
            //Disable the boxCollider so that linecast doesn't hit this object's own collider.
            boxCollider.enabled = false;
            //Cast a line from start point to end point checking collision on blockingLayer.
            hit = Physics2D.Linecast (start, end, blockingLayer);
            //Re-enable boxCollider after linecast
            boxCollider.enabled = true;
            //Check if anything was hit
            if(hit.transform == null)
                //If nothing was hit, start SmoothMovement co-routine passing in the Vector2 end as destination
                StartCoroutine (SmoothMovement (end));
                //Return true to say that Move was successful
                return true;
            //If something was hit, return false, Move was unsuccesful.
            return false;
        //Co-routine for moving units from one space to next, takes a parameter end to specify where to move to.
        protected IEnumerator SmoothMovement (Vector3 end)
            //Calculate the remaining distance to move based on the square magnitude of the difference between current position and end parameter. 
            //Square magnitude is used instead of magnitude because it's computationally cheaper.
            float sqrRemainingDistance = (transform.position - end).sqrMagnitude;
            //While that distance is greater than a very small amount (Epsilon, almost zero):
            while(sqrRemainingDistance > float.Epsilon)
                //Find a new position proportionally closer to the end, based on the moveTime
                Vector3 newPostion = Vector3.MoveTowards(rb2D.position, end, inverseMoveTime * Time.deltaTime);
                //Call MovePosition on attached Rigidbody2D and move it to the calculated position.
                rb2D.MovePosition (newPostion);
                //Recalculate the remaining distance after moving.
                sqrRemainingDistance = (transform.position - end).sqrMagnitude;
                //Return and loop until sqrRemainingDistance is close enough to zero to end the function
                yield return null;
        //The virtual keyword means AttemptMove can be overridden by inheriting classes using the override keyword.
        //AttemptMove takes a generic parameter T to specify the type of component we expect our unit to interact with if blocked (Player for Enemies, Wall for Player).
        protected virtual void AttemptMove <T> (int xDir, int yDir)
            where T : Component
            //Hit will store whatever our linecast hits when Move is called.
            RaycastHit2D hit;
            //Set canMove to true if Move was successful, false if failed.
            bool canMove = Move (xDir, yDir, out hit);
            //Check if nothing was hit by linecast
            if(hit.transform == null)
                //If nothing was hit, return and don't execute further code.
            //Get a component reference to the component of type T attached to the object that was hit
            T hitComponent = hit.transform.GetComponent <T> ();
            //If canMove is false and hitComponent is not equal to null, meaning MovingObject is blocked and has hit something it can interact with.
            if(!canMove && hitComponent != null)
                //Call the OnCantMove function and pass it hitComponent as a parameter.
                OnCantMove (hitComponent);
        //The abstract modifier indicates that the thing being modified has a missing or incomplete implementation.
        //OnCantMove will be overriden by functions in the inheriting classes.
        protected abstract void OnCantMove <T> (T component)
            where T : Component;

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