MissionPlanner.GridUIv2.map_MouseMove C# (CSharp) Method

        private void map_MouseMove(object sender, MouseEventArgs e)
        {
            var mousecurrent = map.FromLocalToLatLng(e.X, e.Y);

            if (mousedown)
            {
                mousedragging = true;

                if (currentmode == mode.panmode)
                {
                    if (e.Button == MouseButtons.Left)
                    {

                        double latdif = mousestart.Lat - mousecurrent.Lat;
                        double lngdif = mousestart.Lng - mousecurrent.Lng;

                        try
                        {
                            map.Position = new PointLatLng(map.Position.Lat + latdif, map.Position.Lng + lngdif);
                        }
                        catch { }
                    }
                }
                else if (currentmode == mode.drawbox)
                {
                    if (e.Button == MouseButtons.Left)
                    {
                        var rect = RectangleF.FromLTRB((float)mousestart.Lng, (float)mousestart.Lat, (float)mousecurrent.Lng, (float)mousecurrent.Lat);

                        list.Clear();

                        // tl
                        list.Add(mousestart);
                        // tr
                        list.Add(new PointLatLng(rect.Top, rect.Right));
                        // br
                        list.Add(mousecurrent);
                        // bl
                        list.Add(new PointLatLng(rect.Bottom, rect.Left));

                        if (boxpoly != null)
                            layerpolygons.Polygons.Remove(boxpoly);

                        boxpoly = null;

                        boxpoly = new GMapPolygon(list, "boxpoly");

                        boxpoly.IsHitTestVisible = true;
                        boxpoly.Stroke = new Pen(Color.Red, 2);
                        boxpoly.Fill = Brushes.Transparent;

                        layerpolygons.Polygons.Add(boxpoly);

                        map.Invalidate();
                    }
                }
                else if (currentmode == mode.movebox)
                {
                    //if (mouseinsidepoly)
                    {
                        double latdif = mousestart.Lat - mousecurrent.Lat;
                        double lngdif = mousestart.Lng - mousecurrent.Lng;

                        for (int a = 0; a < boxpoly.Points.Count; a++)
                        {
                            boxpoly.Points[a] = new PointLatLng(boxpoly.Points[a].Lat - latdif, boxpoly.Points[a].Lng - lngdif);
                        }

                        UpdateListFromBox();

                        map.UpdatePolygonLocalPosition(boxpoly);
                        map.Invalidate();

                        mousestart = mousecurrent;
                    }
                }
                else if (currentmode == mode.editbox)
                {
                    double latdif = mousestart.Lat - mousecurrent.Lat;
                    double lngdif = mousestart.Lng - mousecurrent.Lng;

                    // 2 point the create the lowest crosstrack distance
                    // extend at 90 degrees to the bearing of the points based on mouse position

                    PointLatLngAlt p0;
                    PointLatLngAlt p1;

                    PointLatLngAlt bestp0 = PointLatLngAlt.Zero;
                    PointLatLngAlt bestp1 = PointLatLngAlt.Zero;
                    double bestcrosstrack = 9999999;
                    double R = 6371000;

                    for (int a = 0; a < boxpoly.Points.Count; a++)
                    {
                        p0 = boxpoly.Points[a];
                        p1 = boxpoly.Points[(a + 1) % (boxpoly.Points.Count)];

                        var distp0p1 = p0.GetDistance(mousecurrent);
                        var bearingp0curr = p0.GetBearing(mousecurrent);
                        var bearringp0p1 = p0.GetBearing(p1);

                        var ct = Math.Asin(Math.Sin(distp0p1 / R) * Math.Sin((bearingp0curr - bearringp0p1) * deg2rad)) * R;

                        if (Math.Abs(ct) < Math.Abs(bestcrosstrack))
                        {
                            bestp0 = p0;
                            bestp1 = p1;
                            bestcrosstrack = ct;
                        }
                    }

                    var bearing = bestp0.GetBearing(bestp1);

                    layerpolygons.Markers.Clear();
                    layerpolygons.Markers.Add(new GMarkerGoogle(bestp0, GMarkerGoogleType.blue));
                    layerpolygons.Markers.Add(new GMarkerGoogle(bestp1, GMarkerGoogleType.blue));

                    bearing = ((PointLatLngAlt)mousestart).GetBearing(mousecurrent);

                    var newposp0 = bestp0.newpos(bearing, Math.Abs(bestcrosstrack));
                    var newposp1 = bestp1.newpos(bearing, Math.Abs(bestcrosstrack));

                    boxpoly.Points[boxpoly.Points.IndexOf(bestp0)] = newposp0;
                    boxpoly.Points[boxpoly.Points.IndexOf(bestp1)] = newposp1;

                    UpdateListFromBox();

                    map.UpdatePolygonLocalPosition(boxpoly);
                    map.Invalidate();

                    mousestart = mousecurrent;
                }
            }

            mousedragging = false;
        }