Use a Vector3 to define Z rotation

Questions & Answers
1

I want to use a vector3 to define my Z rotation

How would I go about for example:

Vector3(0,1,0); a Z-rotation of 180
Vector3(0,-1,0); a Z-rotation of 0
Vector3(1,0,0); a Z-rotation of 90
Vector3(1,0,0); a Z-rotation of 270

etc…

2

You could use Euler angles - they are more intuitive, and can be easily converted to quaternions with Quaternion.Euler:

var Z180 = Vector3(0,0,180);
var Z90 = Vector3(0,0,90);
var Z270 = Vector3(0,0,270);

In order to not loose the initial object orientation, save its rotation at Start (it becomes the 0 reference) and combine it with the desired rotation:

private var initialRot: Quaternion;

function Start(){
  initialRot = transform.rotation;
}

// to rotate to the absolute Z270 rotation:
  transform.rotation = Quaternion.Euler(Z270) * initialRot;

// to ADD the rotation Z90 to the current orientation:
  transform.rotation *= Quaternion.Euler(Z90);

NOTE: The latter does relative rotation (exactly like transform.Rotate), and accumulates small errors that progressively tilt the object to weird angles.

3

Thanks for all the previous answers they helped me answer this myself:

Because I wanted my objects right to face the direction I provided, and I only wanted a 2D rotation, I just literally changed its transform.right and adjusted its transform.up by making a cross product of its transform.forward and transform.up

transform.right = direction;
transform.up = Vector3.Cross( transform.forward, transform.up );