Can fog be set to render in reflections?

#1
Another fog-related question:

I am using fog to make the horizon of a ground plane disappear into nothingness.
But in reflections, the horizon still seems to be sharp, as proven by the blur-less reflection in the polyhedron.

Am I missing a setting, or will fog not reflect?

Thanks,

/Fredrik.

reflection+fog.jpg
 
#2
Hm, or wait. Perhaps I'm asking the wrong question.

The reflections in the polyhedron correctly seems to reflect both fog and depth-of-field.
BUT what seems to throw it off is the HDRI.

The fog works as long as it covers a surface, but as soon as it's just nothingness, the hdri map (although not the map itself, but a blurred version of it) supersedes the fog.

Hope you see what I mean — am I doing something wrong here or is this by design?

(I'm using the Cheetah renderer, of course, since the Falcon one doesn't seem to support fog at all, right?)

Again thanks for any help,

/Fredrik.


hdri+reflections.jpg
 
#4
Interestingly, it doesn't seem to matter. However, I am starting to wonder if it isn't actually a philosophical question rather than a rendering one — and if perhaps fog and HDRI cannot per definition coexist.

If my polyhedron reflected the fog, then that would mean fog covered the HDRI "sky", right?
If so, then how could my objects reflect and/or be tinted by that same sky?
So it seems Cheetah deliberately takes the other route and lets the HDRI map supersede the fog, when seen as reflections in objects — or else the HDRI map wouldn't do any good at all in the scene anyway.

I guess this may be hinted at — although not very clearly if I may say so — in the help file under the entry for HDRI:

1541347149185.png


So my guess is I will probably have to experiment with some other way to achieve what I am after.
But again, I'm guessing, so any other thought please let me know. 😊
 

Swizl

Active member
#5
Hmmm, I actually never remembered seeing that note on the HDRI part of the manual. What's even stranger is that it isn't listed in the Fog section. Honestly, I don't even know what that note means. What version of Cheetah are you using? You could try it with some earlier versions to see if it behaves consistently.
 
#8
Well, tried it Cheetah 6, but with the same result — see first image below. It's not identical, but close enough to make me draw the conclusion that if seen in a reflection, HDRI supersedes other backgrounds.

fog and hdri.jpg

The more I think of it, I think this is how it has to be, or HDRI would have no effect at all.

In fact, turning off HDRI gives me the intended floor-fading-into-fog effect, but also, of course, fog being reflected all across the sky (see left image below) which is exactly what would happen if HDRI took the backseat to fog. I guess to a surface, HDRI is basically "what to reflect when there is no other object to reflect", and fog is not an object.

fog only.jpg

So this is all my bad, or at least I think so. My brain still isn't sure it understand what it's talking about.

Which brings me to, though:

Here's a wild and un-thought-through idea: Might it be a potentially helpful feature if fog and HDRI could be set to gradually supersede each other, so that a surface perpendicular to the sky reflected 100% fog and a surface parallell to the sky reflected 100% HDRI instead.
Without taking responsibility for all fathomable ramifications of course, at least in my scene that would provide a gradual dissolve from fog/ground to sky in the ball, and full fog in the vertical surfaces of the polyhedron, sky on top, and fifty-fifty in the slanted ones.
Perhaps that would introduce other problems — but a thought here is it would help get rid of the sudden sharp edge where fog is overridden by the HDRI image.

See below for a mockup (courtesy of Photoshop) of what that would look like in my specific scene. But whether that would be applicable in any other situation is harder to think of at this time of night... 😁

Can I file this as a suggestion?
Or should I just go back to my day job and stop thinking too much?
😄

1541448009446.png
 

Helmut

Active member
#9
* Well, that is what I get:
* Reflection shows a foggy distance where base pattern and fog blend in the distance.
Fog.png
 
#10
* Well, that is what I get:
* Reflection shows a foggy distance where base pattern and fog blend in the distance.
Well — until you turn on HDRI, no?

Because if you do, I predict the fog will
a. outside of the object: look exactly like in your render
b. inside of the object (i.e. in reflections) : stop abruptly at the "horizon", where your base ends.

Or do you actually have HDRI turned on for that render? Because if so there has to be something else amiss in my scene... 🤔
 
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