Hi.
Quick summary : How can I include “GroomComponent.h” from my C++ game project?
…
At first, I have been handling about disappearing fx by using material.
and realized that the material used in hair(GroomComponent) is bit different with others like static mesh or something.
It seems that It’s not affected by opacity, emissive color, and world position offset.
So I had to decide write some special codes for those hair components.
I think the HairWidth variable in GroomComponent could be altenative answer to the problem because this variable quite acting like opacity and emissive color can be replaced to base color.
But,
I can’t include the GroomComponent.h to my c++ project.
I know this sounds somewhat silly but I just can’t. 
How can I include HairStrands files to my project? are those files require some special settings?
and uhm… I want to know is there any clever way to make disappearing fx to the hair component.