In my previous two posts I described the problem of Z thrash in some detail, as well as the problems that polygon offset can have in fixing it. I also described how draping addresses these problems. In this post, I will tr to provide some specific rules for how to overlay geometry in your scenery.
Whenever possible ,use draping rather than polygon offset. If your goal is to put a marking on the ground, draping will always do that correctly, while polygon offset can create artifacts if not used properly.
For x-Plane 9, this means preferring draped .pol files to OBJs for putting markings on the ground.
For x-Plane 10, this means using the upcoming ATTR_draped instead of ATTR_poly_os to put markings on the ground.
When you do need to use ATTR_poly_os in an object, you do not need to increase the number – this number is not a layering indication; ATTR_poly_os geometry is drawn in the order it appears in your OBJ. Always have ATTR_poly_os geometry before any 3-d geometry you might want to include.
Finally, if you use ATTR_poly_os, be aware that you’ll want to use a low layer group like markings; if poly-os geometry is drawn after 3-d, you’ll see artifacts.
