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