Hi everyone, I'm having an issue where creating polys from VDB gives totally different result compared to using straight polys when rendering SSS. I would love to know what it is in the make up of the geometry that makes SSS behave differently cause the geo here is roughly the same thickness everywhere. The brighter one is the straight poly with no VDB in the stream.

Any tips would be greatly appreciated. Thank You!

Have you tried to set the sss "include Mode" to "All Objects"?

I think if you want same result you have to do you convert for both balls individually and then merge

Heileif
Have you tried to set the sss "include Mode" to "All Objects"?

Hello @Heileif, thanks for response, all objects didn't change the result, this would be considered a single object as we are at geometry level and not object level I think.

I think if you want same result you have to do you convert for both balls individually and then merge

Hello @mihatsu, thanks for response, This does produce result as I was expecting, but why doesn't it work the same way with the geometry being one piece with verts merged and all?

Is there some tips we should know when working with SSS and different types of geometry?

Hi, your first image shows two spheres intersecting. Merge is not the same as a Boolean or fuse, it simply merges streams into one. You can tell by looking at the wireframe or polycount.

Instead of using merge, you'd need to use a Boolean union to create a single geometry like your second image.

Rob

robsdesign
Hi, your first image shows two spheres intersecting. Merge is not the same as a Boolean or fuse, it simply merges streams into one. You can tell by looking at the wireframe or polycount.

Instead of using merge, you'd need to use a Boolean union to create a single geometry like your second image.

Rob

Hi Rob, Thanks for responding, Yeah I know the merge doesn't weld the points, I'm guessing the SSS result is still treating the spheres as two separate objects even though its in one object container? This is my first time taking somewhat of a deep dive into SSS.

I've attached a quick hip file that shows the results from doing the following;
Add a colour to each sphere
Use a Boolean or fuse or merge
Add a smooth sop
Use a for-each with a match size
And a key-framed transform at the end

You'll see that both the colour and smooth are affected by how (or if) the geometry is connected.
The match size will depend on how many connected pieces pass through the for-each.
I've key-framed the final transform to show if/how the spheres are connected at the end.

One way to look at this is connectivity and/or manifold vs non-manifold where SSS/rendering isn't the only thing affected by it. (ie. other sops, simulations etc)

I'm not sure if I'm explaining this very well but a geometry container can have multiple unconnected geometries inside it and whether you consider them to be a single "object" or multiple depends on what you are doing. Using the above sops as examples shows how Houdini considers them at geometry level based on connectivity.

Rob

robsdesign
I've attached a quick hip file that shows the results from doing the following;
Add a colour to each sphere
Use a Boolean or fuse or merge
Add a smooth sop
Use a for-each with a match size
And a key-framed transform at the end

You'll see that both the colour and smooth are affected by how (or if) the geometry is connected.
The match size will depend on how many connected pieces pass through the for-each.
I've key-framed the final transform to show if/how the spheres are connected at the end.

One way to look at this is connectivity and/or manifold vs non-manifold where SSS/rendering isn't the only thing affected by it. (ie. other sops, simulations etc)

I'm not sure if I'm explaining this very well but a geometry container can have multiple unconnected geometries inside it and whether you consider them to be a single "object" or multiple depends on what you are doing. Using the above sops as examples shows how Houdini considers them at geometry level based on connectivity.

Rob

Hi Rob, thanks for the HIP file, this was very helpful. Working in SOPS for a while and just realizing a few things because of your file. Thanks again.