First, I clear ZBuffer only per frame. Second, I test with 4 devices with differents GPU, all of them are incorrect.
1, The correct scene, a road with left wall and right wall.
2, The incorrect scene(far):
3, The incorrect scene(close), the road、left wall、right wall seems mixed together, and this position is 5\6 of the road(ring):
4, The incorrect scene(through the mixed-wall-road, the white cubes are waypoints which should upon the road, but there is none of road\wall.
5, Going to fly a while, the start position of the road appear.