if (!pending.empty() && fabs (i.v_position() - pending.back().v_position()) > 1e-4) {
images.push_back (render_line (pending, fonts, target, time, frame_rate));
pending.clear ();
if (!pending.empty() && fabs (i.v_position() - pending.back().v_position()) > 1e-4) {
images.push_back (render_line (pending, fonts, target, time, frame_rate));
pending.clear ();