Hello to all
I've seen all the pretty pictures of clouds and get into problems trying to get my own clouds.
ID3 works fine but if I have two clouds in different z position, the cloud in background always renders in front. Maybe a small problem but I can't find my problem.

Thanks for help

Detlef

Have you tried swapping them round? ie the make the one that is currently in the background be the one in the foreground. I seem to remember something similar where the order in which the i3d clouds were made was important.

Hi Simon,

OK if I change back to front everything is fine. What do you mean with the order in which i3d were made? The date of the file?

No I mean the order you put done the nodes in houdini. if you switch view from tile to list and then to user defined order, that is the order they get rendered in. I think…

And how can I change the order?

Simon would be right and highlights one of the main limitations of fog (atmosphere) shaders in both Mantra and RenderMan (any micropoly renerer really): When using more than one fog object, they are composited in the final image in creation order (or at least in a way that isn't going to work in most cases).

The two best approaches are to:
1. render each cloud separately then composite them together later.
2. Combine both clouds in to a single fog shader.

The first method has the most possibilities as you can use a library approach to clouds. Generate a bunch of ifd files of clouds to disk then render out final images of each cloud. You can get a lot of mileage out of a nice ifd file. You can rotate the cloud in Y to get several different looking clouds.

Thanks a lot for help. Thats the way I've startet yesterady;o) But it don't work for lightbeams and shadows…

Have a nice day

Detlef

It might be worth looking at the lightbeams you can do in cops with a z depth pass. Not sure how well that would work with i3d though…

Thanks a lot!
So I have a lot to do…

Learning is living….

Detlef

Clouds rendered with i3d and fog objects can't casti shadows. They can receive shadows but they can't cast. Since fog shaders are called after all the shading is done (surface and light shaders), there is no way in the renderer to do this.

OK - so I have more to do…

jeff
Clouds rendered with i3d and fog objects can't casti shadows. They can receive shadows but they can't cast. Since fog shaders are called after all the shading is done (surface and light shaders), there is no way in the renderer to do this.

Thats the reason because I prefer to use a surface shader instead of a fog shader.
The other reason is becasue you can use many fog objects without problems.
Like the beggining of the thread, many for shaders cause problems, many objects shaded with a surface shader that uses i3d for volumetric rendering works fine.

Eh, you can cast shadows with i3d files but you have to write a special shadow shader which ain't easy with space transforms etc. Surface shader is easier for sure.

Cheers,

peter B

Hi lisux,

can you help me on my way? What do you mean with
“with a surface shader that uses i3d for volumetric rendering”

winkel
Hi lisux,

can you help me on my way? What do you mean with
“with a surface shader that uses i3d for volumetric rendering”

Take a look at this shader shipped with Houdi: VEX 3D Texture Cloud.
Usually I get the bounding box of my particle system, with metaballs copied on the particles. To get the bounding box use a Bound SOP after your metaballs.
And then shade the bounding box with the VEX 3D Texture Cloud. Try different lighting setups to get the corrects results.
Anyway to get the best from i3D I finally have to develop my own volumetric shader, unfortunately I don't have any of them here bcecause now I am mainly using sprites but I think there are some examples in the exchange.
Viewing the code from VEX 3D Texture Cloud is another good start, and ofcourse Jason's tutorial about i3D:
http://odforce.net/tips/i3d_intro_page1.php [odforce.net]
i3D is great for some effects but my opion is that are very limited and very hard to control, and if you need fine details in your volume you are going to need so much resolution that render times (for the 3D texture) are crazy.

Thanks a lot… sounds funny and I'll try it.

have a nice day!