How to change Polygon Collider based on my animation in Unity3d? - unity3d

Question

I have a small car game, and when I move up/down and left/right, the sprite becomes different. But the physicsbody remains the same. How do I adjust physicsbody? I added a screenshot of my sprite. At the moment I have Polygon physics body as on the right one.
Here is the code that adjusts animation states:
void FixedUpdate()
{
if (Input.GetKey(KeyCode.W)) {
rb2d.AddForce(Vector2.up * physicsConstant);
animator.CrossFade("CarUpIdle", 0);
} else if (Input.GetKey(KeyCode.S)) {
rb2d.AddForce(-Vector2.up * physicsConstant);
animator.CrossFade("CarDownIdle", 0);
} else if (Input.GetKey(KeyCode.D)) {
rb2d.AddForce(Vector2.right * physicsConstant);
animator.CrossFade("CarRightIdle", 0);
} else if (Input.GetKey(KeyCode.A)) {
rb2d.AddForce(-Vector2.right * physicsConstant);
animator.CrossFade("CarLeftIdle", 0);
}
}

Answer 1

To Change polygon based on sprite first you will need to have Serializefield variables to keep track of all the respective colliders. In this script basically what I do is I am keeping all the polygon colliders in array and iterate the array and enable it depending upon the sprite.
In the script im putting the required sprites along with the respective collider for sprite in sequence. So when I request the sprite to change I enable the respective collider and disables the other colliders. You will require something similer like this :
[SerializeField]
private Sprite[] Sprites;
[SerializeField]
private PolygonCollider2D[] Colliders;
private int index = 0;
private SpriteRenderer sp;
void Start () {
sp = GetComponent<SpriteRenderer>();
sp.sprite = Value[index];
}
void OnGUI() {
if(GUI.Button(new Rect(0,0, 80,35), "ChangeSprite")) {
colliders[index].enabled = false;
index ++;
if(index > Value.Length -1) {
index = 0;
}
sp.sprite = Sprites[index];
colliders[index].enabled = true;
}
}
Also in this tutorial it has been explained how to tackle this kind of problem
Unity Game Tutorial
Another way to proceed is to remove the ploygon collider and recreate it
Destroy(GetComponent<PolygonCollider2D>());
gameObject.AddComponent<PolygonCollider2D>();
though this is very bad programming considering I will be creating collider on every sprite change which is heavy on game.