Corona Volume Material Not affecting HDRI background

[aaouviz]

I've noticed this for a long time but never investigated well enough...

Why is it that when I use Corona Sky Environment + Volume Material I get the expected foggy sky... but if I use a hdri as the environment, the foggy sky no longer exists and the background is just simply the hdri unaffected?

Am I missing something? Thanks!

[aaouviz]

Ok, So upon further research I've discovered it seems to work pretty well if I tick the experimental stuff and use 'enviro distance'

[bnji]

Could you please share some screenshots?
I think the difference you can notice it's related to how the HDRI is created. Not every HDR image has a wide range of Exposure Values.

[jms.lwly]

Without seeing your Volume Material setup (you may have already done this, but I assume not) - but you need to change the 'Volume mapping' mode to 'Inside Volume' - it won't do anything with Surface, as there isn't a surface to map the fog onto.

Think that's your fix, but without a screenshot of your setup I can't be certain!

[aaouviz]

Apologies, I thought my explanation was enough.

Please find attached screengrabs of the situation. I'm fairly sure the problem isn't with incorrectly calibrated HDRI's... as this problem has always existed for me.

In any case the problem isn't persisting for me, as you'll see with my fix (attached).

Oh, and James, to answer your possible solution; I'm pretty weary of using 'inside volume' as this seems to absolutely kill the parsing and render times... am I wrong?

Thanks for the reply guys. Let me know if you have further thoughts...

[TomG]

Since an HDRI is "at infinity", the Enviro Distance parameter does indeed determine what Corona should consider that distance as being in regards to things like fog calculations. What was your enviro distance before you changed it? Entirely possible it was set to something that means Corona treats it as being too close for the fog to take effect, depending on the settings for the fog distances.

[aaouviz]

Hi,

Yes, you're correct. When I enabled the debug/extra settings, it was set to only 1000 (I use mm units).... so this is definitely why it didn't work.

Bumping it up to 10000 started to give me some nice results.

[romullus]

Tom, does that means that Corona sky is always at infinite and ignores enviro distance value?

[TomG]

No, other way round :) It's infinite usually (in terms of calculating lighting etc), but for things like fog, Corona has to know what distance to consider it as being at. The enviro distance is what determines that - in other words, "technically this is at infinity, but for purposes of needing to know an actual distance e.g. for fog calculations, treat it as enviro distance"

Otherwise, the HDRI or Sky would always be "full fog" :)

(This is exactly what the enviro distance is for, so everything here is "working as designed")

[romullus]

Ah ok, i got this impression because of the first post of this thread. Thanks for explanation!

[TomG]

NP! TY for asking so I could write it better than first time around lol!