Creating underwater Scene

[AnubisMe]

hey all, I am just wondering if its possible to make a underwater based scene with Corona yet? Caustics, volume fog ect. Right now I am not to sure how to go about it yet. Any advice would be appreciated.

[Juraj]

I am bumping this up because I need to do something similar right now and I've seen Maru post some experimental example somewhere on the forum :- ) Can't find it...

[FrostKiwi]

hey all, I am just wondering if its possible to make a underwater based scene with Corona yet? Caustics, volume fog ect. Right now I am not to sure how to go about it yet. Any advice would be appreciated.

Cheap fakes:
Download a caustics texture and let it render as a textured Corona light = Caustics + reflections and illumination from those and no extreme render times.
Do a Zdepth Pass only for below the water and grade/work it in post.

More elaborate:
from the water surface create a Water Volume and do a Corona Volumetric Mtl. This will give you lightrays (from particles in the water). This will work with the caustics fake from above! So it will be caustic lightrays, including reflections and such and should work.

Difficult:
Combine with a particle system to give lightrays from CoronaVolumetricMtl. some life.

(just some thoughts)

[romullus]

I am bumping this up because I need to do something similar right now and I've seen Maru post some experimental example somewhere on the forum :- ) Can't find it...

Must be here: https://forum.corona-renderer.com/index.php/topic,9728.msg67864.html#msg67864

[Juraj]

Thanks Romullus :- )

I see issue with that given it uses global material. It works for underwater, but what about image that shows both at same time (split horizontally), under and above water ?

Currently necessary to do it in parts ?

I will of course, use every PS trick under sun, but I still would like the most streamlined solution because it quite makes difference.

[romullus]

For such shot i would go traditional way, i.e. model water as big box and assign water material.

BTW, picture in your example is clearly a composite of two separate photographs ;]

[Juraj]

:- ) I just googled first split image that came up.

I wonder then what the original issue was, as it came up quite few times. Creating decently large volume seemed like too obvious solution, so I thought that there would be some issue. Or is the issue only when looking up into surface ?

[Juraj]

I will milk this topic slightly more :- )

Philosophical question of dumb person:

Is material underwater, created as coated wet material ? with darker albedo and that kind of stuff ? Like wet material above ? Or something completely different to maintain the illusion ?

For example, underwater ocean sand.

[maru]

I think there might be some black magic going on under water. Take a look at the photos of coral reef, fish, turtles, or even stones/pebbles underwater, or seen under the water surface from above. There are almost no reflections visible.

[Juraj]

True. The coating is after all part of the overall volume. But does the renderer account for this directly or is such close surface interaction bit outside of it reach ? Well, I'll stick to purely diffuse for now.

[romullus]

I wonder then what the original issue was, as it came up quite few times. Creating decently large volume seemed like too obvious solution, so I thought that there would be some issue. Or is the issue only when looking up into surface ?

I think this idea originated from that discussion about IOR: https://forum.corona-renderer.com/index.php/topic,10383.0.html

[Juraj]

Rendering water stuff really brings out the fact that no caustics at all are possible with Corona currently : /

Yes the fake gives easier, creative results but still..

Edit: O shit, BIDIR still works. Holy Hell ! This stuff needs to get merged....

I mean it only works when I am actually under-water and still can't produce anything if I try to look from above...but very nice otherwise.

Edit2: Just read BIDIR doesn't support absorption :- ( back to zero.. (or using Boris's compositing method and masking it with z-depth to get Absorbtion in caustics)

[spadestick]

One thing I learned is that water material has a "fog property" within the material and not just a tint or diffuse colour.

Like the sand on a tropical clear beach, as the water gets deeper the blue becomes deeper.

[FrostKiwi]

One thing I learned is that water material has a "fog property"

And Corona Mtl has a "absorption" property :]

[maru]

One thing I learned is that water material has a "fog property" within the material and not just a tint or diffuse colour.

Like the sand on a tropical clear beach, as the water gets deeper the blue becomes deeper.

Actually absorption should only be used, unless:
-the water has a layer of some dirt on the surface - use diffuse then, otherwise use pure black, or 0 diffuse level
-the water is colored - then use tint (refraction color)