debug drawer

    [KSPAddon(KSPAddon.Startup.Instantly, true)]
    class DebugDrawer : MonoBehaviour
    {
        private static Material mat;

        private static readonly List<Line> lines = new List<Line>();

        private struct Line
        {
            public readonly Vector3 start;
            public readonly Vector3 end;
            public readonly Color color;

            public Line(Vector3 start, Vector3 end, Color color)
            {
                this.start = start;
                this.end = end;
                this.color = color;
            }
        }

        private void Start()
        {
            DontDestroyOnLoad(this);
            if (mat == null)
                mat = new Material(Shader.Find("Particles/Additive"));

            StartCoroutine("EndOfFrameDrawing");
        }

        public static void DebugLine(Vector3 start, Vector3 end, Color col)
        {
            lines.Add(new Line(start, end, col));
        }

        private IEnumerator EndOfFrameDrawing()
        {
            Debug.Log("DebugDrawer starting");
            while (true)
            {
                yield return new WaitForEndOfFrame();

                Camera cam = GetActiveCam();

                GL.PushMatrix();
                mat.SetPass(0);
                GL.LoadPixelMatrix();
                GL.Begin(GL.LINES);

                for (int i = 0; i < lines.Count; i++)
                {
                    Line line = lines[i];

                    Vector3 screenPoint1 = cam.WorldToScreenPoint(line.start);
                    Vector3 screenPoint2 = cam.WorldToScreenPoint(line.end);

                    GL.Color(line.color);
                    GL.Vertex3(screenPoint1.x, screenPoint1.y, 0);
                    GL.Vertex3(screenPoint2.x, screenPoint2.y, 0);
                }
                GL.End();
                GL.PopMatrix();
                lines.Clear();
            }
        }

        private static Camera GetActiveCam()
        {
            Camera cam;

            if (HighLogic.LoadedSceneIsEditor)
                cam = EditorLogic.fetch.editorCamera;
            else if (HighLogic.LoadedSceneIsFlight)
                cam = FlightCamera.fetch.mainCamera;
            else
                cam = Camera.main;
            return cam;
        }
    }