Solved: Weird hair glitch using Real Hair Shaders

paulawp (marahzen)

I recently bought this hair shader:

https://www.daz3d.com/real-hair-shaders-for-dforce-and-strand-based-hairs

I noticed something weird when I tried testing it with this dForce hair:

https://www.daz3d.com/classic-long-hair-with-dforce-for-genesis-8-females

It leaves spots where the hair is transparent or rippled strangely.

It's a long, straight, unfussy hair with nothing weird about it when using the original material (from the product's set of materials). I tried multiple colors with this shader and the same thing happened, in the same spot. I simulated the hair, and afterward, the blank spots appeared just as before, in the same spots. This was rendered without headlamp on, using some basic lights, and the problem is also readily visible in the viewport (using texture shaded or Nvidia Iray).

I then changed all of the hair settings (length, thickness, etc) back to default; similar glitching remained. I picked the "Before Sim 1" option and simulated again. This actually made the glitchiness worse.

1) Is it that this shader isn't meant for this type of product, in which case, how would I differentiate between it and the sort of dForce hairs it's meant to be used with?
2) If it is a compatible hair, what might cause this sort of problem? 

Attached are examples of the oddity. Glitch 1 and Glitch 2 are the same hair from front and back, when I first opened the file and tried the shader on an existing character. The first shows the transparent spot and the second shows the rippling all the way around the head from that spot. Glitch 3 is after I reset everything. I marked some obvious places where you can see it.

I searched and didn't see any previous references to this type of glitch.

paulawp (marahzen)

And as soon as I wrote all this up and posted it, I figured out what appears to be the problem. I noticed that the shader has one-click tiling options for various settings between x5 through x20, which led to me to realize that this seems to be a tiling glitch. It defaults to x3 when you pick one of these shaders. I found that if I set tiling to x1, the problem goes away; see the attached examples. For this particular hair - and I would guess, other long, straight, sleek hairs like this one - setting tiling to 1x1 manually is something to consider when using this shader.

Spacious

I think that hair shader is meant to be for strand based hair.  Strand based hair inherits it's UV from the hair cap or the geometry of the figure it's on, depending on how it's been set up.  Other types of hairs have a very different type of UV where each strand is actually mapped.  If you've got a strand based hair to try that shader on it will help to understand what I mean.

paulawp (marahzen)

Looking back on the product page, it's a little unclear (to me anyway) the nature of this hair's construction, but I can promise that with the tiling set to 1x1, I am very happy with this shader product on this hair. I'll have to go look through my hair collection for something specifically designated as strand-based and test to see the difference. 

Thanks for your comment. Learning Daz has been an adventure, and I appreciate suggestions and answers to my silly newbie questions.