Make face of 2D ball face direction of movement

Hello Unity Community,

I have a 2D ball with a face. I would like the face of the ball to face the direction of movement after bouncing off a gameobject. I've looked around the forums for examples of how to make the work. The code snippet I found in another post was the closest I got this to work using Quaternion.Slerp. The issue that the rotation is not instant. The face of the 2D ball does face the direction of movement but does so in a "slow" fashion. I know that using 1.0f should make the Slerp "instant" but I am not seeing that. Is it because I'm using "AngleAxis"? Any pointers, corrections, or explanations would be greatly appreciated. Also, 1st time posting on unity forums. Sorry for any errors in not knowing rules for posting. Thanks for any help.

void Start()
{

origVectorPosition = gameObject.transform.position;​

}

void Update()
{

Vector3 moveDirection = gameObject.transform.position - origVectorPosition;

if (moveDirection != Vector3.zero)
{

float angle = Mathf.Atan2(moveDirection.y, moveDirection.x) * Mathf.Rad2Deg;
Quaternion newRotation = Quaternion.AngleAxis((angle), Vector3.forward);
transform.rotation = Quaternion.Slerp(transform.rotation, newRotation, 1.0f);​

}​

}

 

If you want it to happen instantly, probably the easiest way to do it is Transform.LookAt. It will rotate your transform so that its forward is pointing to the specified point you wanna look at. In your IF there, you could just write:

Code (CSharp):

1. Vector3 lookAtPoint = gameObject.transform.position + moveDirection;
2. transform.LookAt(lookAtPoint, Vector3.up);  //assuming y-axis is up in your game

 

I'll give it a shot and report back on my results.

***Doesn't seem to rotate the 2D ball correctly, if it all. Been racking my brain over this issue for a few days now.

 

Hmm...that code should work. If it is not working, then I don't think that the moveDirection vector is correct.

It's a little hard for me to understand what you are doing with that snippet, but at the very least, I do not see any code to actually move the ball. Why is the move direction set to be the vector from the ball's initial position at the beginning of the game to its current position?

Are you using Unity's physics engine to just let the ball drop with gravity and such? If that is the case, try measuring the movement delta each frame, then use that as the moveDirection. Something like this:

Code (CSharp):

1.     private Vector3 previousPos;
2.  
3.     private void Awake()
4.     {
5.         previousPos = transform.position;
6.     }
7.  
8.     private void Update()
9.     {
10.         //vector from position in previous frame to position in current frame
11.         Vector3 moveDirection = transform.position - previousPos;
12.  
13.         if (moveDirection != Vector3.zero)
14.         {
15.             //a point a little in front of where we are
16.             Vector3 lookAtPoint = transform.position + moveDirection;
17.             transform.LookAt(lookAtPoint, Vector3.up);
18.         }
19.  
20.         //this is the key part: remember the where we are this frame
21.         //so that next frame we can measure how far we moved from this
22.         //point.
23.         previousPos = transform.position;
24.     }

 

Why not just: transform.rotation = newRotation; ?

 

I did try that...depending on what "newRotation" is...it either continuously spins or does a slow rotation.

 

Why is the move direction set to be the vector from the ball's initial position at the beginning of the game to its current position?
Interesting, my thinking was that I needed to know the difference in angle or direction using an initial transform. I didn't think it was actually setting the initial value as the current value.

Are you using Unity's physics engine to just let the ball drop with gravity and such?
Yes, I am using unity's 2D physics. The ball itself has a mass of 1 and no gravity or anything else for that matter. So my ball basically has "perfect elasticity" (perfect bounce). I do give the ball an initial velocity to move it.

I will review what I have and report back on what I got. I think having an outside perspective to "bounce" (no pun intended hahaha) ideas off of...helps.

 

From his code it seems he have to LookAt around Z axis.

 

topsekret, thank you so much! You solved my issue in like 2 hours. Is there a place to mark this answered or "upvoted"?

I was able to adapt parts of your code and merge it with what I had before...voila...it worked! The key part was this was this part! previousPos = transform.position;

Here is the complete code that worked for my 2D ball with perfect bounce.

BTW, your previous code worked as well except for the fact that it took 2D sprite and make it face up in the y direction. Otherwise, it worked just as well. I just couldn't figure how to use the code and still have sprite face in the z direction.

void Start()
{
previousPos = transform.position;
}

void Update()
{
//vector from position in previous frame to position in current frame
moveDirection = transform.position - previousPos;
if (moveDirection != Vector3.zero)
{
angle = Mathf.Atan2(moveDirection.y, moveDirection.x) * Mathf.Rad2Deg;
guiAngle.text = angle.ToString();

//assuming front of you ball is normally facing right, add or subtract to/from angle for ball facing other direction
Quaternion newRotation = Quaternion.AngleAxis((angle), Vector3.forward);
transform.rotation = Quaternion.Lerp(transform.rotation, newRotation, 1.0f);
}

//this is the key part: remember the where we are this frame
//so that next frame we can measure how far we moved from this
//point.
previousPos = transform.position;
}

 

Yes, I think that was the issue I was having but I whatever I tried it didn't seem to work correctly but I just finish posting my solution with regard to this. Thanks for your input too, Fraconte!

 

I think you just had to change vector3.up with vector3.forward in LookAt().

To make code more readable look at this: http://forum.unity3d.com/threads/using-code-tags-properly.143875/

 

You are welcome, legendz25. Glad I could help! And I believe Fraconte is correct, changing the Vector3.up to Vector3.forward should make the LookAt work. I overlooked the fact that you were making a 2D game initially lol.

 

Hum..Let me try the forward for the hell of it. Learning something new is always good in my book.

I'll post results.

***Unfortunately, vector3.forward still produces the same results. So strange...even reading online documentation would indicate that vector3.forward should work in this case.

Yes, thanks for the heads up on the code format Fraconte. I'll do that on my next postings.

 

Doing this just to show final solution in a easier to read format. Thanks to Fraconte and topsekret for the help.

Code (CSharp):

1. void Start()
2. {
3.      previousPos = transform.position;
4. }
5.  
6. void Update()
7. {
8.     //vector from position in previous frame to position in current frame
9.     moveDirection = transform.position - previousPos;
10.     if (moveDirection != Vector3.zero)
11.     {
12.           angle = Mathf.Atan2(moveDirection.y, moveDirection.x) * Mathf.Rad2Deg;
13.  
14.           //assuming front of you ball is normally facing right, add or subtract to/from angle for ball             facing other direction
15.           Quaternion newRotation = Quaternion.AngleAxis((angle), Vector3.forward);
16.           transform.rotation = Quaternion.Lerp(transform.rotation, newRotation, 1.0f);
17.      }
18.  
19.            //this is the key part: remember the where we are this frame
20.            //so that next frame we can measure how far we moved from this
21.            //point.
22.            previousPos = transform.position;
23.      
24. }

 

A 2d version of LookAt, which happens instantly, I use this.

Code (CSharp):

1. transform.LookAt (rigidbody2D.velocity + rigidbody2D.position, new Vector3 (0, 0, 1));

That rotates along z-axis.
The velocity + position equals a point just in front of the 2D objects motion of travel. At velocity zero it wont rotate as far as I've tested.
the new Vector3 is just to see that it is z axis without working out if Vector3.left etc is up or whatever.