Live Training 13th June 2014 - Making an "Angry Birds" style game http://www.youtube.com/watch?v=L0tl0CwPYIc

ProjectileDragging.cs

using UnityEngine;
using System.Collections;

public class ProjectileDragging : MonoBehaviour {
    
    public float maxStretch = 3.0f;
    public LineRenderer catapultLineFront;
    public LineRenderer catapultLineBack;
    
    private SpringJoint2D spring;
    private Transform catapult;
    private Ray rayToMouse;
    private Ray leftCatapultToProjectile;
    private float maxStretchSqr;
    private float circleRadius;
    private bool clickedOn;
    private Vector2 preVelocity;
    
    void Awake () {
        spring = GetComponent <SpringJoint2D>();
        catapult = spring.connectedBody.transform;
    }
    
    void Start () {
        LineRendererSetUp();
        rayToMouse = new Ray(catapult.position, Vector3.zero);
        leftCatapultToProjectile = new Ray(catapultLineFront.transform.position, Vector3.zero);
        maxStretchSqr = maxStretch * maxStretch;
        CircleCollider2D circle = collider2D as CircleCollider2D;
        circleRadius = circle.radius;
    }
    
    void Update () {
        if (clickedOn)
        {
            Dragging ();
        }
        
        if (spring != null)
        {
            if (!rigidbody2D.isKinematic && preVelocity.sqrMagnitude > rigidbody2D.velocity.sqrMagnitude) {
                Destroy(spring);
                rigidbody2D.velocity = preVelocity;
            }   
            
            if (!clickedOn) {
                preVelocity = rigidbody2D.velocity;
            }
            
            LineRendererUpdate ();
        } else
        {
            catapultLineFront.enabled = false;
            catapultLineBack.enabled = false;
        }
    }
    
    void LineRendererSetUp () {
        catapultLineFront.SetPosition(0, catapultLineFront.transform.position);
        catapultLineBack.SetPosition(0, catapultLineBack.transform.position);
        
        catapultLineFront.sortingLayerName = "Foreground";
        catapultLineBack.sortingLayerName = "Foreground";
        
        catapultLineFront.sortingOrder = 3;
        catapultLineBack.sortingOrder = 1;
    }
    
    void OnMouseDown () {
        spring.enabled = false;
        clickedOn = true;
    }
    
    void OnMouseUp () {
        spring.enabled = true;
        rigidbody2D.isKinematic = false;
        clickedOn = false;
    }
    
    void Dragging () {
        Vector3 mouseWorldPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        Vector2 catapultToMouse = mouseWorldPoint - catapult.position;
        
        if (catapultToMouse.sqrMagnitude > maxStretchSqr)
        {
            rayToMouse.direction = catapultToMouse;
            mouseWorldPoint = rayToMouse.GetPoint(maxStretch);
        }
        
        mouseWorldPoint.z = 0f;
        transform.position = mouseWorldPoint;
    }
    
    void LineRendererUpdate ()
    {
        Vector2 catapultToProjectile = transform.position - catapultLineFront.transform.position;
        leftCatapultToProjectile.direction = catapultToProjectile;

        Vector3 holdPoint = leftCatapultToProjectile.GetPoint(catapultToProjectile.magnitude + circleRadius);
        catapultLineFront.SetPosition(1, holdPoint);
        catapultLineBack.SetPosition(1, holdPoint);
    }
    
}

ProjectileFollow.cs

using UnityEngine;
using System.Collections;

public class ProjectileFollow : MonoBehaviour {

    public Transform projectile;
    public Transform farLeft;
    public Transform farRight;

	void Update () {
        Vector3 newPosition = transform.position;
        newPosition.x = projectile.position.x;
        newPosition.x = Mathf.Clamp(newPosition.x, farLeft.position.x, farRight.position.x);
        transform.position = newPosition;
	}
}

Resetter.cs

using UnityEngine;
using System.Collections;

public class Resetter : MonoBehaviour {

    public Rigidbody2D projectile;
    public float resetSpeed = 0.025f;

    private float resetSpeedSqr;
    private SpringJoint2D spring;

	void Start () {
        resetSpeedSqr = resetSpeed * resetSpeed;
        spring = projectile.GetComponent <SpringJoint2D>();
	}
	
	void Update () {
        if (Input.GetKeyDown(KeyCode.R))
        {
            Reset ();
        }
	}

    void OnTriggerExit2D (Collider2D other) {
        if (other.rigidbody2D == projectile)
        {
            Reset ();
        }

        if (spring == null && projectile.velocity.sqrMagnitude < resetSpeedSqr)
        {
            Reset ();
        }
    }

    void Reset () {
        Application.LoadLevel(Application.loadedLevel);
    }
}

TargetDamage.cs

using UnityEngine;
using System.Collections;

public class TargetDamage : MonoBehaviour {

    public int hitPoints = 2;
    public Sprite damagedSprite;
    public float damageImpactSpeed;

    private int currentHintPoints;
    private float damageImpactSpeedSqr;
    private SpriteRenderer spriteRenderer;

	void Start () {
        spriteRenderer = GetComponent <SpriteRenderer>();
        currentHintPoints = hitPoints;
        damageImpactSpeedSqr = damageImpactSpeed * damageImpactSpeed;
	}
	
	void OnCollisionEnter2D (Collision2D collision) {
        if (collision.collider.tag != "Damager")
        {
            return;
        }

        if (collision.relativeVelocity.sqrMagnitude < damageImpactSpeedSqr)
        {
            return;
        }

        spriteRenderer.sprite = damagedSprite;
        currentHintPoints --;

        if (currentHintPoints <= 0)
        {
            Kill ();
        }
	}

    void Kill () {
        spriteRenderer.enabled = false;
        collider2D.enabled = false;
        rigidbody2D.isKinematic = true;
    }
}