how do I get dark (black) clouds?

Started by Syx, October 14, 2010, 11:24:44 pm

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Syx

I've tried every setting to get the clouds to block out the sunlight, but to no avail. I've had cumulus clouds a kilometer thick which in the real would would definitely keep the sunlight from getting through and would also look quite stormy, but they still glow as bright as a thin cloud would. Andchanging the cloud's color to black only seems to make it completely vanish from the scene, almost as if the clouds a 'screen' layer in photoshop.

domdib

Syx, this is really a post that should go in Discussion, as it isn't a bug - at least as far as I know. Your problems are puzzling. Have you tried adjusting cloud density?

cyphyr

I don't get why changing the clouds colour to black would "hide" it from the scene, very odd.
However to get the cloud to obscure the sun firstly enable "raytrace shadows" on the cloud layer and then start increacing the cloud density. Also untick "Visable disk" and "Glow in atmosphere" in your Sunlight settings.
Hope this helps.
:)
Richard
Sample attached, plenty of tweaking to do :)
www.richardfraser.co.uk
https://www.facebook.com/RichardFraserVFX/
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Tangled-Universe

October 15, 2010, 03:11:15 pm #3 Last Edit: October 15, 2010, 03:13:39 pm by Tangled-Universe
Richard, do "almost"-black colours work? Say all RGB values @ 1?

Raytrace shadows is not of use to obtain this effect, nor is it recommended to use since you only need it when terrain or surfaces cast visible shadows on clouds or when you want to hide lightsource glow behind surfaces.

Unchecking visible disk and glow in atmosphere is a way. However, the real(istic) trick is the density and depth settings of the clouds.
I'd suggest to increase the depth of the clouds and depth a bit and gradually see how it goes. If you have the desired depth (by look) and density then I'd change some of the lighting parameters. Reducing light propagation should make the clouds appear darker as less light will pass through them.

Syx

It seems to be a volumetric issue. Using 2D clouds I got it to work fine. With 3D though, the clouds just look like a daybreak fog. I'll play with it some more later and see if I can get it to work, as soon as this 10hr render finishes.

One would think though that a volumetric cumulus cloud with a vertical thickness of 7 km would've been more than sufficient to block out the sun, regardless of atmospheric glow.

Tangled-Universe

Quote from: Syx on October 15, 2010, 04:39:03 pm
It seems to be a volumetric issue. Using 2D clouds I got it to work fine. With 3D though, the clouds just look like a daybreak fog. I'll play with it some more later and see if I can get it to work, as soon as this 10hr render finishes.

One would think though that a volumetric cumulus cloud with a vertical thickness of 7 km would've been more than sufficient to block out the sun, regardless of atmospheric glow.


If the density is very low then even 7km thick clouds won't block out the sun. Like with many things in TG2 it's about finding a way to get settings work together.
7km thick clouds probably won't look good so therefore I suggested to first find the desired depth of your cloud and start working from there.

cyphyr

Strange, in the sample above I had a very visible sun with cloud settings as high as 600, default thickness. Only once I had enabled RT did the sun point go away and then I had to start playing with the sun glow settings. Maybe theres a trade off betwen very deep, very dense clouds and less deep, less dense clouds with RT.
??? :)
Richard
www.richardfraser.co.uk
https://www.facebook.com/RichardFraserVFX/
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Ryzen 9 3900X @3.79Ghz, 64Gb (TG4 benchmark 6:20)
i7 5930K @3.5Ghz, 32Gb (TG4 benchmark 13.44)

Tangled-Universe

Quote from: cyphyr on October 15, 2010, 06:19:32 pm
Strange, in the sample above I had a very visible sun with cloud settings as high as 600, default thickness. Only once I had enabled RT did the sun point go away and then I had to start playing with the sun glow settings. Maybe theres a trade off betwen very deep, very dense clouds and less deep, less dense clouds with RT.
??? :)
Richard


I don't see what you mean. The trade-off would be: very deep + less dense or less deep + very dense. Regardless of using raytraced clouds I'd think.
Maybe things get calculated more precise when enabling raytracing, but why and how, I don't know.
I'm 100% sure you shouldn't use it in these situations because the raytracing is meant to be used in case of when terrains/surfaces cast shadows on the clouds.
Interesting find though.

Oshyan

I believe there are some issues with incorrect cloud density calculations which will be fixed in the next update. I'm not certain on that though. Regardless T-U is correct, RT in the cloud settings is necessary for terrain casting shadows into clouds, but should not affect cloud density calculations. Normally it should be kept unchecked (off) since it increases render time quite a lot and seldom do scenes actually need it.

Regardless I've just done a test render in the latest alpha with high density clouds (0.5 density) and medium depth (500m) and it appears to be working correctly. The sun is almost completely occluded, even with Visible Disc enabled.

- Oshyan