Swimming fractals on growing hillsides

Started by ajcgi, August 18, 2011, 10:13:06 am

Previous topic - Next topic

ajcgi

Hey all,
when we did some work not so long ago on growing mountains and the like we found that details were fizzing and swimming all over the place as the height of the mountains changed each frame. Is there any way of locking the fractals down so that they don't vary vertically?
I ask as I'm trying to sort the same issue out again! :)
Alex

Henry Blewer

I did an erosion test animation which had the same issue. The solution has to be done by hand. You need to save the heightfield each time you use the operator. The heightfield needs to be reloaded and the erosion operator applied to that loaded heigthfield.

I do not know how it would be done using a fractal terrain.
http://flickr.com/photos/njeneb/
Forget Tuesday; It's just Monday spelled with a T

cyphyr

Unfortunately since the fractals exist in 3D space what you see is where the terrain intersects with the fractal, so as the terrain changes in the y axis the fractals will change also. The only way I can see to do it would be to render out a very high resolution orthographic view of you area of interest and re map that back onto your terrain. Possibly through the same camera as rendered the map in the first place or as a plan y projection.
Richard
www.richardfraser.co.uk
https://www.facebook.com/RichardFraserVFX/
/|\

Ryzen 9 3900X @3.79Ghz, 64Gb (TG4 benchmark 6:20)
i7 5930K @3.5Ghz, 32Gb (TG4 benchmark 13.44)

Oshyan

How were you controlling your mountain "growth"? If you simply animate displacement amplitude I don't think it should change the structure, but you may be aiming for more complex "growth" than a simple increase in size/height. You could also use a heightfield (derived from a shader if necessary) and animate the Height Multiplier but it would have the same limitations as the displacement amplitude approach. Perhaps a blend of multiple heightfields at varying scales and height multiplication levels...

- Oshyan

Henry Blewer

It would be cool to set up target heightfields. VistaPro had GeoMap (or something like that). It would grow the landscape over set number of frames.
http://flickr.com/photos/njeneb/
Forget Tuesday; It's just Monday spelled with a T

ajcgi

Ok I think there's a little confusion here. My mountain growth is an image map shader, using a 16-bit sgi as displacement. So I increase the displacement value in the displacement tab of the image map shader. The structure itself doesn't change, it's seemingly the fractals applied to that.

Let me give you an example. When the snow appears at the end of the shots (doing a few here) it fizzes into position then finally stops crawling and fizzing as the mountain stops growing. At the start of the shot the grass and soil beneath crawl a lot as though the power fractal nodes are animated. What's apparently happening is the geometry is moving vertically through those fractals giving a crawling effect. When I get this issue in Softimage creating oceans etc I can lock the influence of fractals to X&Y so they don't change with height. That way foam on my ocean doesn't appear to rapidly change shape as it moves about.

Tangled-Universe

Quote from: ajcgi on August 19, 2011, 05:46:14 am
Ok I think there's a little confusion here. My mountain growth is an image map shader, using a 16-bit sgi as displacement. So I increase the displacement value in the displacement tab of the image map shader. The structure itself doesn't change, it's seemingly the fractals applied to that.


Big confusion for me :) You increase displacement, but the structure itself doesn't change?

The topic on growing mountains is on this forum? I'll try to find it to figure out what you mean.

ajcgi

What I'm implying by the structure not changing is that the mountains themselves don't erode over time for example.

Henry Blewer

I added the erosion blurb because I experienced what I thought to be a similar issue.
http://flickr.com/photos/njeneb/
Forget Tuesday; It's just Monday spelled with a T

Oshyan

Ahhh, I think I understand now, and yes this would be due to the 3D nature of the fractals that drive your displacement. So you can either 1: use an image map (several of them perhaps, tiled at different sizes, to avoid repeating patterns) to drive fine detail displacement - this would avoid the variations in procedural noise lookup position. Or you *may* be able to find the right combination of values for Transforming your displacement noise function(s) such that they keep pace with the terrain displacement changes and remain static relative to them. I imagine it would be a bit difficult to do this, especially with ease-in/out in an animation, but if you have a known rate of motion it might be possible. Still the static texture mapped displacement might be easier to implement.

- Oshyan