We do not specifically work on code, but can you tell us what it is exactly you are trying to do? We may or may not be able to help you.
Thank you for the answer.
The sample, the polygon was tried on one.
But I would like to know which polygon is in front,
when two or more polygons exist.
Then, I watched the "buff".
It means distance of the depth direction on 3D-space.
HD graphics 4000 returned zero,
however other video cards returned non-zero.
In the case of zero value,
It won't know the positional relation on 3D-space of two or more polygons.