[Bf-committers] Volume Rendering Updates

[Aurel W.]

Hi Matt,

> This is intentional - since s and a are so closely related (added),
> it's much simpler for a user to just have one control here - having
> two colour swatches to tweak that basically do the same thing makes it
> more difficult to understand how the system works, and what to tweak
> in order to get a certain visual look, and wouldn't really provide any
> more helpful artistic functionality. The absorption is also used as
> the inverse to approximate the resultant colour you get after
> absorption. This is a lot easier to use as an artist than trying to
> think about "if this colour is absorbed, then what gets left over".
Well, it's certainly a good thing to add some abstraction on top,
which makes control easier for an artist. After all, it's not about
physical based rendering, but features which give artistic control.
But I would really like to have a correct volume ray caster, which
solves the RTE correctly for the single scattering case on the bottom
of this. There is just one defined way to do this right and someone
needs to stick to the basic math of it.

I have to look into this, I can't remember exactly what the
irregularities in blenders implementation are. But as far as I can
remember this ends up in different sigma_a for the three RGB channels,
but sigma_s is equal for all channels. Or do I remember incorrectly in
this case?

There are also a lot of available publications, with measured sigma
values in RGB space for all different kind of materials. So I guess
it's important to be able set these,... it would also be possible to
provide presets.

But of course I agree that there is a need of easy artistic control,
which the current implementation provides. But as I said it would be
possible to come up with nice and easy mappings from values which
provide easy control, to the correct RTE parameters. As it is done
with absorption at the moment, to reverse this and provide a tinting
option.

At least I think, this would need some review and maybe work, which I
am happy to provide. But this sigma_s and sigma_a issue is just a
minor problem for me atm.

I can get a patch ready in 1-2 weeks and may also include some stuff
which wouldn't be ready or intended at all to be merged, just for
review. But I guess in the end it won't be just a one shot
(patch->apply) commit, which I have to do. So I understand this rather
as a proposal, to commit to the volume renderer for some time. ;)

aurel