The way 'path length' affects shadows cast by hidden parts of OOT Super Sleeky Hair

kataiarpad

Normally opacity controls the amount of light that can pass through a surface. If you set it to zero the surface completely disappears in the render. Obviously it won't cast any shadows either. This is also true if only a part of the surface is made see-through by using an opacity texture.

Well OutOfTouch's Super Sleeky Hair behaves differently. It has a very nice feature that lets you control the hair's length. This is accomplished by using opacity textures. But even the invisible parts still cast some shadows. (See 1st picture 'shadows').

I consider this an issue with the product but that is not what this post is about. I keep product complaints to PMs as a courtesy towards the artists. The reasons I'm still creating this post are two-fold:

1. The workaround I've found may be useful to others
2. OutOfTouch didn't respond to me since weeks either here or on <major competing website> so I'm assuming they chose to ignore this issue (or me for whatever reason)

With all that out of the way, here's the solution. Tweaking path length setting in render settings / optimization can for some reason get rid of the unwanted "phantom shadows". See attached pictures.

Let me assure you that this is not caused by some special configuration. The scenes are all using the default environment settings that come with Daz Studio. I've discovered this issue a few months ago and it persisted through all the DS versions since then. The pictures below are from the latest DS beta version. Also as you can see in the pictures there is nothing in the scene besides a V7 and the hair itself.

So what is path length? AFAIK it controls the number of bounces light can make. The default setting is -1. I can't be sure what that means exactly without seeing the code but normally that means infinite. I've seen someone in these forums writing that G3 eyes need a setting of at least 6 to properly render. Apparently this hair needs around 30 for whatever reason. If someone would care to enlighten me on this I'd be grateful.

TL;DR: If you are rendering a shortened version of OOT Super Sleeky hair and want to avoid "phantom shadows", set path length to at least 30 in render settings / optimization.

tn222eb

thank you so much for creating this thread, i had this problem for a long while and finally with your help i got it fixed