Alain <aze### [at] qwertyorg> wrote:
> You want to model a lump of foam, but you model a box filled with smoke.
> That's not the same thing.

Both media show the physical process of scattering due to scatterers (quote from
wikipedia: "The types of non-uniformities which can cause scattering, sometimes
known as scatterers or scattering centers, are too numerous to list, but a small
sample includes particles, bubbles, droplets, density fluctuations in fluids,
defects in crystalline solids, surface roughness, cells in organisms, ...")

The idea was to use the media scattering to exploit the (probably) higher
efficiency and not modeling the micro cells of the foam explicitly.

The objective is to get the scattering look of a dense media, without overly
bright surface. Single foam cells do not need to be visible. The picture I
posted was a little misleading in this aspect, but it shows nicely the desired
light glow at the edges of surfaces in shadow areas.

> Despite the dimention of your object, your media is not what I call dense.

How could the density be increased? Setting the scatter rgb to higher values
leads to way to high brightness levels on the surface. Using attenuation and
extinction this could be fixed, but was not changing the demonstrated visibility
issues.

And what I still don't get is why a simple division of the same media into
several boxes yields a completely different result.

> You should try with an isosurface using some function that have
> repeating holes, like leopard. Use "all_intersections. Use a material
> with some transparency, an interior with an ior of about 1.4 to 1.7,
> fade_color fade_distance and fade_power 1 or fade_power 1001.
> The texture should have some transparency:
>   rgbf<Red_Value, Green_Value, Blue_Value, 0.7>
> Add some specular to the finish: specular 0.5 roughness 0.01.

My first try was actually to model the foam cells explicitly, I used a script
generated mesh2 with irregular cells for this purpose. Due to the numerous
partly filtering surface layers there was actually no need for fading, but the
light glow due to scattering was not very realistic. And the performance was not
very good, especially with the high number of cells needed to get a fine foam.

Whats wrong is not the foamy look of the surface, but the feature visibility of
objects in the media. If they are behind the media volume, the suddenly
disappear -- instead of fading away with distance. This effect is demonstrated
in the model I posted: just increase the number of media slices, and the object
visibility changes despite the fact that the media effectly stays unchanged and
is only distributed along several boxes. This seems quite illogical to me.

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