Rotating a 3D object on the Y axis relative to the cursor's position?

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I'm trying to combine the implied camera perspective of classic 2D Zelda titles with the controls of twin-stick shooters, in 3D. I can move the player with the WASD keys, but I'm not sure how to rotate him to face the mouse cursor. I think I need to do the following:

Calculate the cursor's position on the screen.
Draw a line between that position and the player character.
Calculate the difference between the player character's current Y axis rotation and that line.
Rotate the player character on the Y axis by that difference, so that the difference becomes 0.

This way if the player moves the cursor to the top of the screen the character will look "North"; if the player puts the cursor in the bottom left corner, the character will look "Southwest", if that makes sense.

I tried using transform.LookAt, but this caused a crazy feedback loop that made the character spin out of control:

   Ray mouseRay = playerCamera.ScreenPointToRay(Input.mousePosition);
   float midPoint = (transform.position - playerCamera.transform.position).magnitude * 0.5f;
   transform.LookAt(mouseRay.origin + mouseRay.direction * midPoint);

I also tried the Brackey's tutorial here, but was unable to calculate the lookDir because ScreenToWorldPoint returns a Vector2, while a 3D object's transform.position is a Vector3.

Any ideas?

Answer 1

Best Answer

Answer by Acegikmo · Apr 28, 2020 at 08:37 PM

I'd raycast against a mathematical plane at the height of the player, then use look rotation!

 Ray mouseRay = playerCamera.ScreenPointToRay(Input.mousePosition);
 Plane p = new Plane( Vector3.up, player.position );
 if( p.Raycast( mouseRay, out float hitDist) ){
     Vector3 hitPoint = mouseRay.GetPoint( hitDist );
     player.LookAt( hitPoint );
 }

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umbralogian · Apr 28, 2020 at 10:41 PM 0

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Thank you for your answer, @Acegikmo! I've accepted this one because of your idea to bounce the Raycast off of a plane at the height of the player character ins$$anonymous$$d of whatever the cursor happens to be over. $$anonymous$$y testing found that this prevents the character rotation from "hanging" on bumps in the terrain or obstacles placed upon it!

abssuper20 · Dec 15, 2020 at 09:55 AM 0

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Your answer is exactly what i was looking for @Acegikmo. But the rotation gets messed up when the mouse is exactly over the player. it keeps rotating around itself like crazy. How do i solve that?

Answer 2

Answer by Cassos · Apr 28, 2020 at 08:44 PM

So sounds like you just need help with the player looking at the mouse. This should work out:

     void Update()
     {
         Ray ray = cam.ScreenPointToRay(Input.mousePosition);
         RaycastHit hit;
         if (Physics.Raycast(ray, out hit))
         {
             transform.LookAt(hit.point); // Look at the point
             transform.rotation = Quaternion.Euler(new Vector3(0, transform.rotation.eulerAngles.y, 0)); // Clamp the x and z rotation
         }
     }

It will the player rotate on the y-axis only. To be honest, I'd add a Vector3.Lerp just to make it more smooth! ^^

Greetings,

Max

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umbralogian · Apr 28, 2020 at 10:34 PM 0

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Hi @Cassos, thank you for your answer! I'm not familiar with Vector3.Lerp; how would it fit into this?

Cassos umbralogian · Apr 29, 2020 at 10:31 AM 0

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It basicly just smooth out the rotation so it doesn't instantly turn to it but needs some time

ShahinBhai · Feb 22 at 06:09 PM 0

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It's worked for me.. Thank you

Rotating a 3D object on the Y axis relative to the cursor's position?

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