Draws camera oriented wire sphere using Handles.

UnityEditor.Handles.DrawCameraOrientedSphere.cs

void DrawCameraOrientedWireSphere(Vector3 position, float radius, Color color) {
    UnityEditor.Handles.matrix = Matrix4x4.TRS(Vector3.zero, transform.rotation, Vector3.one);
    UnityEditor.Handles.color = color;

    UnityEditor.Handles.DrawWireDisc(position, Vector3.right, radius);
    UnityEditor.Handles.DrawWireDisc(position, Vector3.up, radius);
    UnityEditor.Handles.DrawWireDisc(position, Vector3.forward, radius);

    if(Camera.current.orthographic) {
        Vector3 normal = position - UnityEditor.Handles.inverseMatrix.MultiplyVector(Camera.current.transform.forward);
        float sqrMagnitude = normal.sqrMagnitude;
        float num0 = radius * radius;
        UnityEditor.Handles.DrawWireDisc(position - num0 * normal / sqrMagnitude, normal, radius);
    } else {
        Vector3 normal = position - UnityEditor.Handles.inverseMatrix.MultiplyPoint(Camera.current.transform.position);
        float sqrMagnitude = normal.sqrMagnitude;
        float num0 = radius * radius;
        float num1 = num0 * num0 / sqrMagnitude;
        float num2 = Mathf.Sqrt(num0 - num1);
        UnityEditor.Handles.DrawWireDisc(position - num0 * normal / sqrMagnitude, normal, num2);
    }
}