VRayEnvironmentFog and volumetric beams of light

[G0M0]

Hello

I'm trying to achieve volumetric beams of light coming through windows - like on picture below - there i've manage to do this by using dustdevil plugin.



I tried many combinations of parameters of VRayEnvironmentFog but i always end up with total blackness / no beams at all / partial beams but with errors in other parts of image.

Once I was able (using phoenix 1.1 - cant reproduce / find scene), with some negative values in density, to achieve something what i'm looking for, but - beams was additive and it generated bugs with GI.

What possibly I am doing wrong?
Is there any way to do this?

Thanks in advance for answers.

[LarsSonparsson]

EnvironmentFog can be tricky. I'm usually creating fake workaround with it to get the light beams visible without rest of the "darkening" fog.

Create a copy from the keylight and set it to exclude lighting to all (or include lighting to none), so it won't light anything, but will still cast shadows.
For environment fog, include that copied light only. Set fog distance to 1000m to 5000m or so (depends on the scene scale). That will make fog so thin, that it is almost invisible. Now when boosting light intensity to really high values (insane values, extremely crazy values!) like 1 000 000 or 5 000 000, the light beams will show up.

Simply the point is to create so thin fog that it comes invisible and light that fog with really bright light without ruining rest of the scene.

Try it. It really works.

[Jiri.Matys]

Yep, I use this method for a long time (since environmentfog show up) for some scenes and I have to agree, it works.

[G0M0]

thanks a lot - i'll try out yours solutions :]

[rivoli]

you can also achieve good results comping the volumetric pass in post. I believe vray2 has a vrayfog render element which makes life easier..
in 1.5 you override any mat with a solid black one, tweak the fog and basically end up with a fog pass that can be easily comped with the beauty render. it offers more control than trying to do everything in one pass.

[Dariusz Makowski (Dadal)]

Heya


LarsSonparsson any chance for teapot scene?

[LarsSonparsson]

Here's simple setup.
Should show the idea I was talking about.




Env_Teaspot.zip

[Dariusz Makowski (Dadal)]

Woho thanx alot ! Will check it out at some point

Btw any idea how to cast only shadow? Without all that white lights...

[G0M0]

The solution with duplicated light works fine for me (except high values of subdivs), but I'm afraid for long term use it would be complicated with usage of many lights.
About compositing - I usually try to avoid this technique - due low experience in that field, I'm also afraid it would complicate work with GI affecting Fog and vice versa.
But considering PDPlayer as a tool for compositing it would be perhaps a solution for the future (when I finally get some time to learn it).