Question

I have this enemy class, and I want it to

1) Spawn at a certain place Vector3 pos

2) Rotate to face my player position

3) Move forward

As this code is now, it will appear at it’s specified place: pos, and attempt to rotate to face it’s target: targetShip. It fails to correctly face it’s target, because of this offset.

If I remove the code that assigns a value to translation, or if I normalize pos then the model will appear at the origin and rotate to face it’s target correctly.

If I try to move it at all using any of the comment out code regarding translation, It appears to start someplace else and I never can find it.

However, if I remove the code relating to rotation, and uncomment the code relating to translation, then I can get it to move forward.

The trick is doing it all together.

class Enemy : BasicModel
{


    Matrix rotation = Matrix.Identity;
    Matrix translation = Matrix.Identity;
    public Vector3 pos, up, right, targetShip,dir;

    public Enemy(Model m, Vector3 pos)
        : base(m)
    {
        up = Vector3.Up;
        //sets the position to the Vector3 as it's spawn point.
        translation = Matrix.CreateTranslation(pos);

    }

    public override void Update()
    {
        //Glo is a global class, where I store the player world.
        targetShip = Glo.world.Translation;
        targetShip.Normalize();

      pos = transform.Translation;

      rotation = RotateToFace(targetShip, pos, Vector3.Up);
      //Attempt at moving the model forward. Causes it to go out of view
      //translation *= Matrix.CreateTranslation(this.GetWorld().Backward);
      //translation *= Matrix.CreateTranslation(pos);
    }

    public override Matrix GetWorld()
    {
        return rotation * world * translation ;

    }

    /*Params: O = Our target
     * P = Our position
     * U = up.
     * 
     * Code from some site I googled up.
      */
    Matrix RotateToFace(Vector3 O, Vector3 P, Vector3 U)
    {

        //The direction we're facing.
        Vector3 D = (O - P);
        //Our relative Right.
        Vector3 Right = Vector3.Cross(U, D);
        Vector3.Normalize(ref Right, out Right);
        //Our back
        Vector3 Backwards = Vector3.Cross(Right, U);
        Vector3.Normalize(ref Backwards, out Backwards);
        //Our relative up
        Vector3 Up = Vector3.Cross(Backwards, Right);
        //Make a matrix out of all of these.
        Matrix rot = new Matrix(Right.X, Right.Y, Right.Z, 0, Up.X, Up.Y, Up.Z, 0, Backwards.X, Backwards.Y, Backwards.Z, 0, 0, 0, 0, 1);
        return rot;
    }



}

}

—-

---

I tried doing

anathonline’s method, and here’s what I have now
It doesn’t work. I can’t see my model anywhere.

public override void Update()
        {
            targetShip = Glo.world.Translation;
            targetShip.Normalize();

            //Translate it to the origin
            translation = Matrix.Identity;
            //Orient it
            rot = RotateToFace(targetShip, translation.Translation, Vector3.Up);
            //Move it back to where it was originally;
            translation = Matrix.CreateTranslation(offset);
            //Calculate the front of the object
            Vector3 front = Vector3.Forward * translation.Translation;
            //normalize it
            Vector3.Normalize(ref front, out front);
            //multiply it
            front *= 2;
            //translate the object
            translation *= Matrix.CreateTranslation(front);



        }

        public override Matrix GetWorld()
        {
            return world * rot *  translation;

        }

—-

---

2nd revision: Still doesn’t work

public override void Update()
    {
        targetShip = Glo.world.Translation;
        targetShip.Normalize();


         translation = Matrix.CreateLookAt(offset, targetShip, Vector3.Up);
        var amountToMove = 0.2f;
        var finalPos = Vector3.Lerp(targetShip, offset, amountToMove);
        rot = translation * Matrix.CreateTranslation(finalPos); 


    }

    public override Matrix GetWorld()
    {
        return world * rot * translation ;

    }

Answer 1

I fixed it, don’t worry. All of this code is obsolete anyway.