I think I found the problem. If anybody runs into a similar issue, seems with the update of both plugins, for whatever reason Forest Pack made alpha not fuctional on the old vray material. I recreated the grass from scratch and now its matching again.
Not sure which causes the problem, but thats the solution.
What do you mean with FP made alpha not functional on the old vray material?
Which is/was correct?
So in a nutshell. When I opened up the same scene file now with Vray6 my Forest Pack materials on the grass did not have a functional alpha anymore. What I mean by that is, the alpha texture was in there, it was turned on, but instead of making the black elements transparent it just filled the black areas with black diffuse. Forcing all extra parts of my grass to render black. I had to assign a fresh Vray material an then the alpha worked proper again. No clue why this happened but it happened on 3 completely different scene files with different grass elements/textures.
Make sure to report this to Itoo, bacause it can be very annoying to assign new VRay materials to all geometry that has alpha maps assigned!! (I am thinking of collections of Maxtree, Globe plants, etc, etc)
Did you test the geometry if it worked without being in a FP object?
This sounds like a huge bug though.
Yeap, emailed them as well.
I will have to explore my other scene files to see if maybe it was a unlucky glitch in the 3 scene files that I was working in currently, but if this does happen on all old scene files this can become a long time consuming process to revise materials with alphas.
Me starts itching:( Certainly a reason to wait for a solution. There also are lot of libraries out there that use Forest presets and/or alpha mapped geometry, so it is important where exactly this error is coming from. I mostly wait a few months before switching to a new version, so can’t help.
hahahaa! Same here. I have learned from the past when Vray updates they tend to create issues to features that were always working perfectly fine, so I usually also wait for at last a 2nd release to help fix problems. But with their Sky system and Vray Decal Displacement I couldn’t wait. Now its just problems here an there lol.
So I looked at some of my other heavy FP scene files and they seem to be fine as well. No idea why some of my other assets got weird. I did however figure out what is causing the opacity slot not to work. Its the “Fog Color”. Somehow on the files with issues, the fog color is black instead of white.
That’s something that can easily be scripted, or solved with MMZorb. But still…it’s annoying.
I did however figure out what is causing the opacity slot not to work. Its the “Fog Color”. Somehow on the files with issues, the fog colour is black instead of white.
So the fog colour changed when you opened the scenes with newer versions?
I tested a simple scene with a leaf (opacity) and latest versions of V-Ray and Forest Pack but everything seems fine. However if I set the fog colour to black, the opacity affected areas then renders black but this is expected.
I don’t know whether it’s related but there was this post which flagged a bug Opacity mapped objects reflect as fully opaque. - V-Ray GPU :: Issues - Chaos Forum
Could it be that between versions the fog default colour was changed, thus causing an issue?
I don’t think it is related. The thread you are referring to is about V-Ray GPU. Actually we are all looking at V-Ray CPU here right?
That was definitely not the case.
Interesting thread, please keep any finding coming.
Oh ok…just a thought 
Dit you check whether the v5-file had black fog values while rendering OK? If not: how did v6-files suddenly have black fog values?
This is what I am not 100% certain about. If the black value changed on its own or if Vray5 had it as well but it was working properly. What I do know is the scene did not change 1 bit on my end from good to bad render. I updated Vray and had to start rendering final assets for a client project, then noticed my envionrment looking different than before so had to start narrowing down the source.
At this point I do not want to really downgrade once more to Vray5 to figre out more about this, at least now I see what caused Alpha to not work so I can fix it quickly. Luckily all my other big fpack scene files are rendering as they were which is wonderful.
If you could pass us a scene, we’d be grateful.
Hi I tested the following - created a scene in 3ds max 2022/v-ray 5 with black fog colour and rendered, here is the result:
I then opened the same scene in 3ds max 2023/v-ray 6 and rendered and here is the result:
I don’t know why it renders differently as you can see in V-Ray 6 all the opacity affected areas render as black.
I am not using forest pack - just a plane with VRayMtl assigned to it and a dome light.
This might be a bug, let me do a bit more research and I will get back to the thread to eventually share the info or report it as a bug.
The blackness disappears when thin-walled is checked.
I’d chalk this to a bug, as opacity should not have anything to do with the fog color.
Run the script below to fix the offending materials while the devs work on a proper fix.
for m in ( getClassInstances vrayMtl) where (m.texmap_opacity != undefined and m.texmap_opacity_on) do m.refraction_fogColor = white
