Hi,

I wanted to dig deeper into volume rendering, but I encountered something strange.
With the basic smoke and billowy shader, the density parameter seems to have no effect. I checked the vop network which seemed fine, and tried to replace it a parameter of my own. And this time it has an effect, when it's 0 I get nothing, but I get a cube of smoke instead of a sphere of smoke, and the render looks weird.
I really don't understand what's going on.

As a side note, the way the billowy smoke shader is made, the amplitude for the noise has no effect.

I'm using 9.1.244.

Thanks for any help

I've been looking at this myself and I'm equally bemused about Houdini's volumetric renders. Can I ask what your appying the shaders too?

I seem to get the best results using an ISOoffset, so increasing the density does give me noticible results with this SOP.

Looks like my first post was incomplete ops: , I wanted to write that I apply the shader to one metaball, with “metaballs as volume” checked.

To be sure the density is effecting the shader I've run a small quick test. Seems to work fine…

Do you have any links for ‘plain english’ explanations of volume rendering/shading? - I'm finding it hard to find anything that doesn't require a PHD in maths! :?

Looking at billowy_smoke :

In the first post the parameter node in question is “density” which, as i understand it, is used to get the “density”-named attribute from the actual volume. That parameter is also toggled as “invisible” and doesn't show up in the material interface.

When you replaced it with your own constant parameter, you got a volume of constant density.

Steve C has probably been modifying the “Smoke Density” parameter in the material interface, which is different from plain “density”.

eetu.

(hope i got it right..

Steve C has probably been modifying the “Smoke Density” parameter in the material interface, which is different from plain “density”.

Yep - that is what I was doing.

Thanks a lot, that makes sense
Actually, the density parameter is not hidden (using 9.1.244 here), wether for the volume cloud, billowy smoke or basic smoke shader, which is what confused me…

Silly me, I'm used to using Cd and Alpha in my shaders, so the geometry attributes get used in the shader, but not density!