Perpendicular rotation

Unity Engine
1

Hey, my question is how do i instantaite the object, so that the spawn would always be perpendicular to another object, and rotation as well. I want the Y axis to alwyas be perpendicular to the line, even if the line has rotated. Its simply a Ray, drawn from one gameObject, to another.

Image:
Here you can see that the y axis is not perpendicular to the line, and im having this bullet rotation problem.
http://s3.postimg.org/okebhlr83/Left.png

-Thanks! :)))

2

Have you tried setting transform.right to the direction of the line? This should align the red arrow with the line.
Otherwise regular trigonometry should let you calculate the z angle your sprite needs to have its up axis align with the red line.

3

Here’s how it’s done using trigonometry: (C#)

using UnityEngine;
using System.Collections;

public class Align : MonoBehaviour {
    // Move the from and to transforms in the editor at runtime and watch the align transform align and place itself in between.

    public Transform from;
    public Transform to;
    public Transform aligned;
    void Start () {
        if (from == null)
            from = new GameObject ("from").transform;
        if (to == null)
            to = new GameObject ("to").transform;
        if (aligned == null)
            aligned = new GameObject ("aligned").transform;
    }
   
    void Update () {
        Vector2 offset = to.transform.position-from.transform.position; // Get an offset vector, get the opposite and adjacent of a right triangle
        float radian = 0f;
        if (offset.x != 0f) {
            radian = Mathf.Atan (offset.y / offset.x); // Arc tangent of opposite/adjacent to find angle
            if (offset.x < 0f) {
                radian += Mathf.PI; // enable 360 degrees, disable if you want green line above red at all times
            }
        }
        aligned.eulerAngles = new Vector3 (0f, 0f, radian * Mathf.Rad2Deg); // Set the angle.

        // Debug stuff:
        aligned.transform.position = (from.transform.position + to.transform.position) * 0.5f;
        Debug.DrawLine (from.transform.position, to.transform.position, Color.red);
        Debug.DrawLine (aligned.transform.position, aligned.transform.position + aligned.transform.up, Color.green);
    }
}