How to draw a circle around a moving game object

Questions & Answers
1

I made a function to draw a circle around a given position, with a given radius:

    // Draw circle on XZ plane
    private void DrawCircle(Vector3 position, float radius)
    {
        var increment = 10;
        for (int angle = 0; angle < 360; angle = angle + increment)
        {
            var heading = Vector3.forward - position;
            var direction = heading / heading.magnitude;
            var point = Quaternion.Euler(0, angle, 0) * (position + direction * radius);
            var point2 = Quaternion.Euler(0, angle + increment, 0) * (position + direction * radius);
            Debug.DrawLine(point, point2, Color.red);
        }
    }

However, this circle gets drawn around the origin 0,0 instead. Can someone tell me what I’m doing wrong, also links to any resources would be great. Thanks!

2

Well, your code doesn’t make much sense to me. First of all your “heading” value doesn’t seem to contain any meaningful value. You essentially mirror your position vector to the other side around the world origin and add 1 to the z component. So it’s a position just on the other side of the origin. You then normalize that direction.

Next you multiply that unit vector by your radius and again add your position. Finally you rotate that position around the world origin. I guess you wanted to do something like this:

var point = position + Quaternion.Euler(0, angle, 0) * Vector3.forward * radius;
var point2 = position + Quaternion.Euler(0, angle + increment, 0) * Vector3.forward * radius;

Though since Debug.DrawLine only has an effect inside the editor, you could simply use Handles.DrawWireDisc. However DrawWireDisc can only be called from a rendering callback. For example in OnDrawGizmos / OnDrawGizmosSelected, OnGUI, OnSceneGUI, … Without more context it’s not clear when or for what you need this circle-