Author Topic: Volumetric's like I'm 5  (Read 685 times)

2021-12-23, 06:52:03

caspian

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I'd appreciate a little help understanding the volumetrics. I've read the CommonPoint posts (https://thecommonpoint.com/blog_volumetrics#right) which made lots of sense while I was reading it, but when trying to apply fog to any of my scenes I keep failing.
I thought I'd set up a super basic scene so I could try to understand how the Absorption and Emissions relate. But I still can't work it out. I just keep pumping in random numbers and crossing my fingers.
What I want to achieve is the ability to make my scenes have foggy atmosphere so I can then play with god rays and stuff, but if I can't understand volumentrics I'm never going to get that working!
Thanks in advance.

2021-12-23, 13:53:12
Reply #1

Nejc Kilar

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Haha, I'm still laughing at the title, well done sir!

So what I'm about to write down is supposed to be taken as mostly oversimplification but hopefully it'll be a bit useful to you.

You can perhaps kind of think of absorption as a parameter that will affect how deep the light rays will go inside the volume. The deeper they go (and depending on the setting) the dimmer they'll become. So eventually after traversing through the volume for a certain distance, they'll be smothered. So kind of like saying after a certain distance the ray will completely "disappear". If you add color to the absorption then you know it's a similar story except only a certain light wavelength (color) will bounce back to your eyes.

So thinking about it like that the absorption will mainly only result in things becoming dimmer. (again, trying to oversimplify things).

Then, when you add scattering you can think of adding some "substance" to the volume. Tiny particles that will cause the light to scatter and not just pass through the volume in a straight line. Now once the light starts scattering that's when the visual magic happens because then you'll get the "god ray" effects going and all those fun things.helpdes

Emission then sort of adds some kick to the light as it travels through the volume. So light as it passes through the volume it will gain emissive properties (think glowing plasma effects).

Again, I'm trying to oversimplify things here and I'm not sure its entirely helpful but... Hopefully it helps :)
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2021-12-23, 13:58:37
Reply #2

Beanzvision

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2021-12-23, 18:40:47
Reply #3

caspian

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"Emission then sort of adds some kick to the light as it travels through the volume. So light as it passes through the volume it will gain emissive properties (think glowing plasma effects)."

– Thanks Nejc! This is the kind of metaphor I was hoping for and it is starting to make sense.

Is Distance is always distance from camera, not distance from the edge of the object?

If a volume material Emission is 1000cm is the 'plasma effect is zero the closest to camera, rising to max strength at 1000cm? Remembering how fog appears IRL...(https://unsplash.com/photos/EUPGjs5Vf4o) I'm thinking that this might be right, as it's more glowy as it becomes thicker. So probably I'm guessing that it becomes max 'plasma effect' at 1000cm in this hypothetical.

2021-12-25, 13:37:07
Reply #4

ingemar

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Quote
Is Distance is always distance from camera, not distance from the edge of the object?

Yes, that’s the way I believe it works. Always relating to the active (rendering) camera.