CCW_FLAG_DC
for (last = first; last->flags & (CCW_FLAG_CC | CCW_FLAG_DC); last++);
ccw[-1].flags |= CCW_FLAG_DC;
for (last = act; last->flags & (CCW_FLAG_CC | CCW_FLAG_DC); last++);
ccw->flags = CCW_FLAG_DC;
#define ccw_is_chain(_ccw) ((_ccw)->flags & (CCW_FLAG_CC | CCW_FLAG_DC))