// during pointer motion, select/toggle pictures between initial x/y (param)
// and current x/y (get pointer)
private void UpdateRubberband()
{
// determine old and new selection
var old_selection = rect_select;
selection_end = GetPointer();
var new_selection = BoundedRectangle(selection_start, selection_end);
// determine region to invalidate
var region = Region.Rectangle(old_selection);
region.Xor(Region.Rectangle(new_selection));
region.Shrink(-1, -1);
BinWindow.InvalidateRegion(region, true);
rect_select = new_selection;
UpdateRubberbandSelection();
}
