hi
I want to build a ice material to this model .
so ,i used multiSSS vop to wire a material.
but ,if i set scattering distance to 15,the effect at top and bottom is what i want .but the middle part is too dark.
if i set scattering distance to 50,all body of the model is bright,but the foot is daker.

how to improve the effect?

thanks

It depends on the scattered points on the surface. Are they evenly scattered? It will help if you can post a hip file.

Cheers!
steven

thank you .
A hipnc file is already in sss.rar attatchment.

I think your main problem is the gilight – the sss vops don't play well with it (at least not as written). I'd suggest using an environment area light instead, and then if you want “GI” in the sense of multiple bounces, use PBR.

I've changed a few things in your hipfile to show this. Play with the scattering distance and render with the Mantra_PBR rop. This is set up with 2 bounces.

A couple of things to look at:
1. I tied the number of points in the cloud to the shader's scattering distance (and the ROPs save the cloud before rendering).
2. For ice, you might consider adding direct transmission and/or reflection. For the transmission case, its intensity can be tied to the scattering distance (reinterpreted as optical depth). I added this to your shader so you can play around with it.
3. In PBR, the SSS component has to be reinterpreted either as a constant, or as emission (Ce export). In your shader, I set it to emission. This should get picked up as secondary contributions by other objects (but not by the ice's own bsdf's I don't think, unless you use the isotropic bsdf, maybe, but that's a different animal).

Anyway… hope that helps.

Hi Mario,

I took a look at the shader inside the file you posted, and it looks really intriguing. Thanks for posting it! However, when I clicked render, all I got was a black image, yet the glacier's outline was in the alpha channel. The point cloud was being generated correctly, so I'm not sure what the problem is with it.

(I opened the hip file from flyingc and it rendered with no problem)

I would really like to examine what was done inside those reflected light and transmission loops more closely.

josh3light
However, when I clicked render, all I got was a black image, yet the glacier's outline was in the alpha channel. The point cloud was being generated correctly, so I'm not sure what the problem is with it.

Hmm… it's working fine over here (downloaded from my own post).
Are you sure you're using the “Mantra_PBR” ROP?
PC written correctly? (load it as a geo file to check)
Write permissions?
Don't use IPR (just to remove one possible variable, though it seems to work fine too)
Rendering from cam1?
Using H10?

nice example mario thx

speaking of the isotropic bsdf, is there any way to control the density in the shader?
had a look at the vex bsdf isotropic (), it has a “viod” between the ()…
any ideas?

thx
jason

Hi Mario,

Yeah its really weird. I've never had an example file just not work before like this, everything I've tried in houdini on this computer has worked for months now. the PC file is written fine and everything. Using H10.0.334, winxp 64 sp2, I tried to render it several ways, pressing the render button, rendering from the viewport using the icon… downloaded the file again and clicked render without changing anything….

Thanks for downloading and checking it again though, I'll try to figure out the problem on my end.

Mario Marengo
I think your main problem is the gilight – the sss vops don't play well with it (at least not as written). I'd suggest using an environment area light instead, and then if you want “GI” in the sense of multiple bounces, use PBR.

I've changed a few things in your hipfile to show this. Play with the scattering distance and render with the Mantra_PBR rop. This is set up with 2 bounces.

A couple of things to look at:
1. I tied the number of points in the cloud to the shader's scattering distance (and the ROPs save the cloud before rendering).
2. For ice, you might consider adding direct transmission and/or reflection. For the transmission case, its intensity can be tied to the scattering distance (reinterpreted as optical depth). I added this to your shader so you can play around with it.
3. In PBR, the SSS component has to be reinterpreted either as a constant, or as emission (Ce export). In your shader, I set it to emission. This should get picked up as secondary contributions by other objects (but not by the ice's own bsdf's I don't think, unless you use the isotropic bsdf, maybe, but that's a different animal).

Anyway… hope that helps.

thank you for your nice file,Mario
l have learned your file for some days.but still have several questions.

1.what is the difference between the SSS single vop and the SSS multi vop?
2.in your network ,there is a constant vop named black which seemly has no use. what is the function?

This presentation of Mario's offers a lot of insight about the implementation. Page 2 answers your question about single vs. multi.

http://forums.odforce.net/index.php?app=core&module=attach&section=attach&attach_id=1266 [forums.odforce.net]

josh3light
However, when I clicked render, all I got was a black image, yet the glacier's outline was in the alpha channel. The point cloud was being generated correctly, so I'm not sure what the problem is with it.

I have exactly the same problem. I'm using 10.394

brianBurke
This presentation of Mario's offers a lot of insight about the implementation. Page 2 answers your question about single vs. multi.

http://forums.odforce.net/index.php?app=core&module=attach&section=attach&attach_id=1266 [forums.odforce.net]

thank you

but i can't find the second part of the article,could you post the adress?

flyingc
2.in your network ,there is a constant vop named black which seemly has no use. what is the function?

Probably the value of the “false” case in an If-Then VOP (I don't have it open in front of me, but that's likely what it is; either that or some constant which becomes a default value when some conditions are not met).

flyingc
but i can't find the second part of the article,could you post the adress?

There's no second part to that talk, I'm afraid. There was only time to cover multiple scattering. Single scattering was left for “some later time”, which never actually happened. But I wouldn't worry about it. I put it in there for completeness, but it will be pig-slow with area/environment lights (it'd be better to give it its own light category so it picks up purely directional lighting, than to blindly throw it in with the entire illumination).

To test it, just put a single point light behind the ice and enable only single scattering, then play with the SSSSingle parameters. Then, if you feel you like/need the effect, add the necessary VOPs/Parms to support separate light categories for each reflectance component (as you'll need to be able to limit single scattering to only a “key” light, else it will become too expensive to use).

HTH.

(darn, I broke my “666 posts” )

here,why reflect Vector can't be used directly?