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Animated/evolving Volume Fog


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#1 French_Fry

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Posted 12 March 2014 - 12:25 AM

Hey guys,
maybe a simple question, but I've been banging my head over this. How do you animate the fog in a volume fog node. When I mean animate, I don't mean translating the fog in x,y,z, I'm trying to have the fog evolve. I have a fast noise piped into the volume fog with a high seethe rate, but that is there to change the aspect of the fog, and doesn't affect how the fog would evolve. I thought maybe I could animate the first time slice, but that basically pops from one frame to another.
I feel like I'm just a click away..or at least should be by now. Any tips?

Thanks

#2 isotron

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Posted 12 March 2014 - 04:50 AM

it should depends on the fastnoise, by animating the brightness contrast, but u need to animate in steps like u set up your slices. F.E. u have 100 slices in your fogtool and want to animate the evolve from 0 to 10 . u need the keys set to : frame0 = 0-100 same value in the fastnoise, frame1 = 101-200 same value...and so on...
didnt know how to make it more clear with my english ;) maybe u have a sample comp?

#3 French_Fry

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Posted 12 March 2014 - 10:27 AM

Thanks Isotron...I don't know if I understand completely. Can you explain "set to: frame0 = 0-100 value in the fastnoise"?

#4 ChadCapeland

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Posted 12 March 2014 - 10:40 AM

Sadly, no, you must animate the FirstSliceTime for each frame you want. So if your volume has 100 slices, you'd set FirstSliceTime to Expression = "time*100".

You would then need to cycle the volume so that the Seeth is Expression = "math.floor(time/100)*x" where x is your desired seething rate.

It would be nice if VolumeFog supported something like AT's Quilt format, where you encode all the Z slices into one ginormous image. Fusion easily handles 32K images, and could sort of handle even larger (ever make a 3D LUT with very high precision?). The Quilt has metadata that allows you to know what the XYZ sizes and aspects are, so you wouldn't need a UI change to VolumeFog, either.

#5 French_Fry

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Posted 12 March 2014 - 11:13 AM

Ok, thanks Chad! That seems to work..gets things animated. I would have never figured out the math for that.
My only concern now is that since the look of the fog is based on the seethe rate ( high detailed fog= high seethe rate), if I want the fog to evolve nice and slowly, I need a lower seethe rate, which then lowers the detail the fog. Is there a way to counter that effect?

#6 ChadCapeland

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Posted 12 March 2014 - 04:27 PM

You can't use SeethRate at all. That's a time function, not a depth function.

Hmm... Actually looking at the tool, they don't have a Z transform built in, so I guess Seethe is the Z. But that doesn't give you anything to actually animated the volume with. Sorry, I've used VolumeFog a lot, but never with FN.

Maybe try Darktree?

#7 French_Fry

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Posted 12 March 2014 - 05:21 PM

Ok, but I don't quite get how you get interesting looking volume without the seeth rate though. Isn't the seeth rate what alters the appearance of the volume in it's depth, giving it irregularities?

#8 ChadCapeland

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Posted 12 March 2014 - 05:37 PM

I think Seethe is just a Z translate.

EDIT: Yeah, that's exactly what it is. Check out FastNoiseTexture to see what I mean.

I'm pretty sure this is simplex noise, which can be higher dimensionality, but only a 3D implementation is available in FastNoise.

So yeah, either use Darktree, some other noise generator, or make a 4D noise fuse. What kind of animation were you hoping to see?

#9 French_Fry

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Posted 12 March 2014 - 10:28 PM

Aha...that makes sens. I think we have an old copy of darktree laying around here somewhere. I just hope I'll have time to get it installed and working.
As far as the look, I just have some fast noise node node with discontinuous/inverted noise merged creating some interesting "stringy" fog I would love to get evolving somewhat. It's for a full cg show, so not realistic or matching footage. Thanks for pointing me in the right direction!




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