   Viewport maxZ = 0 question
  I have a 3D arrow mesh (cylinder + cone) that I use to indicate light direction.  I want this to always be visible, so I tried setting the MinZ = MaxZ = 0 in the viewport transformation and it works well.However, after thinking about it, I started questioning why it works.  The arrow has overlapping triangles from some view angles, so shouldn't this cause some sort of Z-fighting since both pixels will have a z = 0 from this viewport transform?  But rotating the arrow and viewing from all angles, there is no problem.  It almost seems like it does the depth test first (with z values before flattening from the viewport transform), and then flattens to z = 0 from the viewport transform.I am using Direct3D 9.Any explanation?   