Cloud Overhangs

Mohawk20 · August 13, 2008, 05:14:31 AM

This is a thread I started on Ashundar to address a problem I had, for which I did have a solution.
The result of my solution was unexpectedly nice, and so I want to share the basics of that thread here.
(I have to cut it up in posts because of the attachment size issue.)

The problem I had was that when playing with cloud formations I often had the 'problem' that the clouds didn't have as much overhangs as I would like. Most of the time they look just like normal mountains, while nice thunder clouds can look like pillars with overhangs.

Has anyone else ever thought about this?

The solution I used was a Redirect shader, like in the first image below.

The first two render images are from one render, but the first is standard bmp output, and the second is the tone mapped exr output.

Mohawk20 · August 13, 2008, 05:19:37 AM

This result lead me to adjust the internal Gamma settings.
The result of that can be seen in the 1st image below.

A comment of old_blaggard was: "These are looking good. I like how you're achieving detail without having the clouds look too hard and sharp."

And my reaction was: "Well, in this case the Edge Sharpness is 20.3059, and the Cloud Density 0.0165039"
That might help a lot of people to get nice clouds even without the redirect shader.

The 2nd image was the first of two more test renders with the sun low on the horizon. These were not tone mapped, they're just the raw bmp output. The other is attached to the next post.

Mohawk20 · August 13, 2008, 05:24:24 AM

Finally here is the last render, not tone mapped. I was amazed by the detail in colour and variety in shape and density.
So much depth in the image, just because a redirect node...

I also have attached the tgd of this last image for you to play with.

I hope this leads to some amazing results. I've seen a few test renders from TerrAde at Ashundar which are VERY nice.

rcallicotte · August 13, 2008, 08:59:42 AM

Oooh. This is kinda cool.

Hetzen · August 13, 2008, 09:50:00 AM

That's really impressive.

So I had a play with your .tgd file to see how it worked (1st image), and thought, why not replace the Power Fractal with a Density Fractal with the same settings apart from the displacement (to my logic it's just a black and white image), maybe that would speed up the render. The result is the second image. Then I thought, surely the original Density Fractal controls the hight, so turned off the Y input (3rd image).

Hrm. Nothings changing, so I directed the original Density Fractal into the Cumulus Layer, skipping out the redirect node (4th Image). Again no change.

I set these preview renders with 1/1 GI, as this is just for bouncing light rays around, shouldn't have much effect on the cloud structure, so I thought. Is this the case, or am I doing something more fundamentaly wrong?

All render times were pretty much the same @6mins on my machine.

I really like the idea of distorting the X,Z along Y. Especially if I have a specific cloud I want to copy. Or am I again not grasping the subtle changes these nodes make?

Mohawk20 · August 13, 2008, 11:21:41 AM

My guess is that high res renders will at least show more small detail and realism than change the overall large shape.

However, it might be that the effect is all in the original input and that the redirect doesn't do anything.
The concept of changing the shape of clouds like this remains functional however, as proved by TerrAde's warped clouds.

Tangled-Universe · August 13, 2008, 02:17:06 PM

Quote from: Mohawk20 on August 13, 2008, 11:21:41 AM
My guess is that high res renders will at least show more small detail and realism than change the overall large shape.

However, it might be that the effect is all in the original input and that the redirect doesn't do anything.
The concept of changing the shape of clouds like this remains functional however, as proved by TerrAde's warped clouds.

Perhaps using a warpshader instead of redirect?

I don't know which image you mean from TerrAde

Mohawk20 · August 13, 2008, 04:43:03 PM

I mean this image: http://www.ashundar.com/gallery/displayimage.php?pos=-5500
He started experimenting with this after reading my thread about this on Ashundar...

Hetzen · August 13, 2008, 05:17:31 PM

Mohawk, don't get me wrong, I'm trying to piece this program together with very little experience with nodes, and bugger all documentation. I really am not trying to pull apart your idea. Your method has opened up another kernal of imagination towards solving a problem, maybe the Warp shader is the way to go (sounds as if it should with a name like warp).

Trust me, I sat through hours of video trying to get a handle on how clouds work in Vue, until the point I realised the person demoing it had no real idea either!

At least in Terragen 2 there seems to be more access to more bespoke methods of achieving what you set out to do, and that the program at least allows us to think outside the box.

Tangled-Universe · August 13, 2008, 05:23:34 PM

Quote from: Mohawk20 on August 13, 2008, 04:43:03 PM
I mean this image: http://www.ashundar.com/gallery/displayimage.php?pos=-5500
He started experimenting with this after reading my thread about this on Ashundar...

Ah I see...those are some wicked structures

However, it is clearly mentioned that he used a warpshader for this and not a redirect shader. I'm afraid your are mistaking somehow.

Mohawk20 · August 13, 2008, 05:38:47 PM

Quote from: Tangled-Universe on August 13, 2008, 05:23:34 PM
Quote from: Mohawk20 on August 13, 2008, 04:43:03 PM
I mean this image: http://www.ashundar.com/gallery/displayimage.php?pos=-5500
He started experimenting with this after reading my thread about this on Ashundar...

Ah I see...those are some wicked structures

However, it is clearly mentioned that he used a warpshader for this and not a redirect shader. I'm afraid your are mistaking somehow.

No, I'm not mistaking... This is his second try, his first try was with the redirect shader.
Anyways, it's still within the boundaries of using other shaders to affect the standard cloud shaders.

Tangled-Universe · August 13, 2008, 05:48:19 PM

I never said it wasn't

I'm just not really convinced the redirect shader really adds what you describe, like Hetzen showed.
I also tried it myself some very long time ago, but honestly that was also during my extreme tg-n00b time

I'll see if I can get something nice out of it when I've time.

Martin

Hetzen · August 13, 2008, 06:22:35 PM

I think now, the Cloud Shader doesn't allow an X,Y,Z input. Just a 2D image to do it's thing. I've tried using the Warp shader, and all I get is a difference in coverage. Not a series of overhangs.

Mohawk20 · August 14, 2008, 03:27:24 AM

Well, this was the initial reason to start this topic on Ashundar. 'Has anyone be able to...'

I got some nice clouds here, but maybe it was just luck.
Does anyone have any serious experience with this?

moodflow · August 14, 2008, 04:26:33 PM

Hi Mohawk,

Hopefully Matt or Oshyan can chime in here, but as far as I know, and from the many tests I've done over alot of time, I believe the clouds only work off of a 2D input, X and Z (just as a standard 2D heightfield does). The Y component is ignored as far as I can tell.

Hopefully one of them will answer as we've all seen clouds with overhangs. My only guess is, the cloud shader takes additional information from the 2D image to generate additional 3D detail, such as not only using the 2D function to generate a planar map, but also a height map (since we can all see gaps in the clouds). I'd love to find out what the cloud shader is really doing, as this would make designing clouds much easier.