// FIXME-DRAGDROP: Settle on a proper default visuals for drop target.
payload.Preview=was_accepted_previously;
flags|=(g.DragDropSourceFlags&ImGuiDragDropFlags_AcceptNoDrawDefaultRect);// Source can also inhibit the preview (useful for external sources that lives for 1 frame)
payload.Delivery=was_accepted_previously&&!IsMouseDown(g.DragDropMouseButton);// For extern drag sources affecting os window focus, it's easier to just test !IsMouseDown() instead of IsMouseReleased()