Velocity to 2D rotation (angle from velocity vector with atan2)

Questions & Answers
1

Im working on a side scroller game. I have projectiles that have velocity, but don’t have an angle, while the particles attached to those projectiles need it to rotate properly (on the z-axis)

I’ve seen people recommend Mathf.Atan2, but when I use it the particles only rotate properly when both x and y are either positive or negative (and even then it goes in the wrong direction when getting close to the axes), so:

  • when I shoot a projectile upwards, particles’ rotation is around 0 (perpendicular, aiming to the right)
  • when its to the left, the particles are aiming down
  • when shooting down, the particles aim to the left
  • when shooting right, the particles aim upwards

here’s the code:

private void ControlDirection ( Vector3 direction )
{
    float angle = Mathf.Atan2( direction.x , direction.y ) * Mathf.Rad2Deg;
    transform.rotation = Quaternion.AngleAxis( angle , Vector3.forward );
}
2

It’s Atan2( Y , X )

 float angle = Mathf.Atan2( direction.y , direction.x ) * Mathf.Rad2Deg;

Then, either:

transform.rotation = Quaternion.AngleAxis( angle , Vector3.forward );
or:
transform.rotation = Quaternion.Euler( 0 , 0 , angle );