DIR_FROM_DXDY
p.new_dir = DIR_FROM_DXDY(xdiff, ydiff);
p.new_dir = DIR_FROM_DXDY(sp->beacon[n].x - p.xpos,
p.new_dir = DIR_FROM_DXDY(sp->exit[n].x - p.xpos,
p.new_dir = DIR_FROM_DXDY(sp->airport[n].x - p.xpos,