PLEASE explain Volume Mask/Fog to me

Hello,

This is unbelievable, it's been since fusion has been released for free that I struggle JUST to make it work.

Most of the it doesn't work and the mask is everywhere like a pixelated texture that kind of follows the pattern of the image, unusable.

And sometimes it worked, with the same setup, same position pass from the 3d program, without knowing why it worked.
Then, happy with this new discovery, I open the comp another day to test another sequence, and it doesn't work back again!?

This is driving me nuts, what is going on?
I do everything that it's been told in every single tutorial on the subject.

Is there any special secret information that I'm missing?

I hope that somebody could help.

Thank you in advance.

If someone want to ask me if I did "this" or forgotten "that", I don't think I forgot anything, and I followed this tutorial step by step dozens of time:

Could you post an example of your composition and maybe one rendering? Most of the time it's better to see what you have and give advice on that

Nothing against the thread starter, but we're seeing this type of thread on this forum a lot. I have no idea what response they are expecting when they aren't offering any helpful information about the issue they have. I feel like tossing out equally unhelpful advice like "Did you check your numbers?" or "Try the slider." or "Make sure your render is OK."

Thank you everybody for your inputs.

I know that my thread could be seen as vague, but if you read it again, it really offers all information needed.

The problem is obviously in another point of the workflow, and that was what I was hoping for: information that I don't have and that is not explained in the tutorial.

I couldn't have answered you that I tried to push/pull this slider, or enable this or that function, except by the affirmative, because the fact that I did every single step mentioned in the tutorial, dozens of times, and verified them again and again... and again, over a period of three years, is self-explanatory and leaves no need to explain more my case, or show screenshots.

So it seems that I found the issue, and it that it is maybe because the version 7.5 that I use, is different from the 6.2 of the tutorial:
I went to the world position pass loader node, and discovered that, in the "format" tab, there are channels as well. So I tried to set x, y and z position(s) to r, g and b, and it seems that this was the missing point.

This is not explained in the tutorial.

And this is the point : without knowing your input sources we couldn't know you have a separate render with the wpp inside which you use to copy the info into the actual render.

If you use the same render for both inputs you can get rid of the channel boolean and set the channels of the wpp in the first/main render. Then the information is already in the stream of tools and can be used by the volume tools

I think the tutorial is very clear that the second render has the wpp information in the rgb channels and not in any other.

Actually, I made the exact same setup as the tutorial, and my wpp is rgb render as a separate file (just like the tutorial).
Thank you for the tip, but I'm not sure I understood completely, can you elaborate a little more please?