Cloud Busting

Tangled-Universe · August 19, 2010, 07:02:38 AM

You can't split the output of a powerfractal into components?

Hetzen · August 19, 2010, 07:10:44 AM

Yes you can, but what I'm looking for, is noise that doesn't change through altitude/y. If you just take the x and z, it will change the higher you look at the noise. I think.

dandelO · August 19, 2010, 07:37:42 AM

I'm not sure I get your meaning of a 2D fractal. It's only 3D when volume or displacement is added.
Is it like an alpha mask, black and white, with no range, so the border of B/W is the only area where there's noise?

MGebhart · August 19, 2010, 08:00:49 AM

Excellent post.

Hetzen · August 19, 2010, 08:13:18 AM

I think the best way to describe what I'm looking for, is when you use a heightfield from a map, white equals the peaks, black the valley. So you extrude out from a flat plane.

With PFs you have this plane, but it evolves through y, so each plane slightly changes as you reference it against a new y position.

You can see this when you stick a PF or DF into a cloud node. What you get are blobs of noise. Clouds.

But when we apply displacement on the ground, we don't see sperated blobs as we apply displacement through y. To prove this, your displacement value as you change it always keeps the same form, but in relative scale to the displacement.

What I need is a noise I can apply to the clouds, that has no change in pattern through y.

dandelO · August 19, 2010, 08:33:59 AM

Instead of making your fractal 'Y stretch' zero, make it larger than the total cloud layer depth.

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It's still placed by a simple shape circle just for visibility, with complete white to black falloff to the edge in one, no falloff in the next. The fractal is flattened to b/w only. I imagine you want to warp or deform those pillars, If I understand correctly?

schmeerlap · August 19, 2010, 08:41:39 AM

A really, really useful topic. Those fragmented bits of stray cloud always bugged me. I've downloaded this topic for further study.
Thanks Hetzen, dandelO, et al for the work you guys put into this.

John

Henry Blewer · August 19, 2010, 08:57:11 AM

Yes there has been some real gold being posted here lately. I am tired of the stray cloud parts also. I have been masking them out lately. I have been using power fractals to blend out the naughty cloud parts. Using the same seed as the density shader for the cloud seems to work. Changing the noise makes things more interesting.

Hetzen · August 19, 2010, 09:20:38 AM

Quote from: dandelO on August 19, 2010, 08:33:59 AM
Instead of making your fractal 'Y stretch' zero, make it larger than the total cloud layer depth.

[attachimg=#]

[attachimg=#]

It's still placed by a simple shape circle just for visibility, with complete white to black falloff to the edge in one, no falloff in the next. The fractal is flattened to b/w only. I imagine you want to warp or deform those pillars, If I understand correctly?

Thanks Martin. But that's not what I'm looking for. Attached is the sort of thing. I need varrying shades of 0 to 1 to subtract from the cloud DF.

The problem is keeping that pattern as you apply it to PFs through y. Hence why I used an HF. I suppose I can use a bitmap, but then you still have the resolution issue.

Hetzen · August 19, 2010, 09:21:50 AM

Weird. The image I attached seems to have appeared in your post. LOL

Hetzen · August 19, 2010, 09:36:43 AM

I also now think I'm talking bollocks. I've asumed that I'd be subtracting from the top of the cloud, when in fact I haven't. Time to move onto plan B. Sorry guys.

dandelO · August 19, 2010, 09:47:17 AM

Oh, Christ!

I just looked outside, by the way, the clouds are lovely. I need to get out more!

Hetzen · August 19, 2010, 09:54:05 AM

Tangled-Universe · August 19, 2010, 11:29:34 AM

Quote from: dandelO on August 19, 2010, 07:37:42 AM
I'm not sure I get your meaning of a 2D fractal. It's only 3D when volume or displacement is added.
Is it like an alpha mask, black and white, with no range, so the border of B/W is the only area where there's noise?

I think this is correct for a powerfractal, but I'm not sure if that would also mean for the cloud-fractal or at least the way the cloud-node treats the fractal which it is fed with.
But, not very important now probably.

For an X,Z-only fractal I thought you can also feed a PF into the color-input of a surfacelayer and use that?
Or you could use the PF as a blendshader for a pure white surfacelayer? Same trick, slightly different.

The color-input does not accept/deal displacement so you should end up with a flat texture I'd tend to think.

Hetzen · August 19, 2010, 12:01:52 PM

Well I said there was a plan B.

Just needed a few extra blue nodes.

Attached is an aerial image showing the mountain range of clouds. Notice no clipping at the top of the range. Yes there is some flatness on the nearer clouds, but I think I can add some more billows into the HF to deal with that.

I've also attached the network. This time I've created a gradient from 1000m to 7000m (my cloud range, ie alt 4000m, depth 6000m) I then compare this altitude gradient with the HF. If the HF is greater than the altitude gradient then allow the Density Fractal, if not then 0. There's also another conditional there to say if the HF = 0 then no cloud, so that the crop is to the bounds of the HF.

Anyway, it's a lttle long winded, but the shapes I feel are quite natural I guess, and what I'd expect to see from these sorts of clouds. The great thing is you can more or less draw what you want like you would landscape relief.