[Bf-committers] Cycles + AO + Transparency

[Jason Wilkins]

Maybe I should have qualified my statements and said that AO is more
physically-based than alpha transparency

:-)

Or, maybe I was thinking that ambient light ceases to be ambient when
it passes through a transmitter/reflector.  It should become something
like "ambient transmission" or "ambient reflection".

On Mon, Apr 23, 2012 at 3:51 PM, François T. <francoistarlier at gmail.com> wrote:
> well that's because AO is not physically correct, not because you are not
> applying it correctly or not.
> even ambiant light would get transformation through glasses, which "basic"
> AO won't take in consideration. But it seems that AO cycle is a bit
> different according to Bretch.
> yet most of the time, people do not use AO like it should be though. IMO AO
> should be used as follow : (AO*ambiantLight)+otherLights+diffuse,....
> But even like that, it wouldn't be so correct, because ambiant light going
> through glasses in real life should get transform.
>
> my 2 cents again
>
> 2012/4/23 Jason Wilkins <jason.a.wilkins at gmail.com>
>
>> I would tend to agree with François, ambient occlusion is function of
>> 3-space where ao(x,y,z) is the proportion of the solid angle around
>> that point that contains geometry that blocks ambient light.  All
>> geometry, even transparent geometry, blocks ambient light.  So, if you
>> are seeing darkening on a refracting or reflecting surface it is
>> because you are not combining ambient occlusion correctly, not because
>> the AO has been calculated incorrectly.  A refracting or reflecting
>> object really does block ambient light 100% and only lights other
>> surfaces through caustics (or itself through transmission).
>>
>> If a surface is partially refractive or reflective, but also diffuse,
>> then only the diffuse part should be affected by AO.
>>
>> If it is because the object has alpha transparency then that is not a
>> physically based kind of lighting and then there really isn't a
>> "correct" answer.  People might give different answers if you asked
>> them should the object give AO to itself vs contributing to other
>> objects in the scene.  From Brecht's explanation it sounds like Cycles
>> just ignores this kind of transparency for global illumination
>> purposes.
>>
>> On Sun, Apr 22, 2012 at 5:21 PM, Brecht Van Lommel
>> <brechtvanlommel at pandora.be> wrote:
>> > Augustin is right, it works, but only for the Transparent BSDF. In
>> > Cycles, Transparent is defined to work as, "render as if there was no
>> > geometry there", which also affects AO and shadow rays.
>> >
>> > The case could be made that the Glass BSDF should also work this way
>> > for AO rays, but it gets fuzzy then, where depending on the particular
>> > settings of a BSDF it may seem a good/bad idea to make it transparent.
>> > Right now there's a clear and consistent rule at least, and you can
>> > control it with the light path node.
>> >
>> > Brecht.
>> >
>> > On Sun, Apr 22, 2012 at 11:32 PM, François T. <francoistarlier at gmail.com>
>> wrote:
>> >> As AO is geometry based, as far as I know, it is not supposed to make
>> >> difference on its transparency, as at least the basic algorithm only
>> check
>> >> for mesh data, but not the material.
>> >>
>> >>
>> >> 2012/4/22 Agustin Benavidez <agustinbenavidez at gmail.com>
>> >>
>> >>> I am pretty sure it does work with transparent BSDF, and not with
>> caustics
>> >>> i.e. using glass bsdf , so if you are using glass bsdf, use light path
>> node
>> >>> to switch to transparent bsdf at least for shadow/diffuse rays or
>> whatever
>> >>> ray you need.
>> >>> Cheers
>> >>>
>> >>>
>> >>> 2012/4/22 Tobias Oelgarte <tobias.oelgarte at googlemail.com>
>> >>>
>> >>> > I made some experiments with Cycles today and I noticed that AO sees
>> all
>> >>> > faces as opaque, like the internal Renderer did. That means that a
>> face
>> >>> > with glass material (entirely or nearly entirely transparent) will be
>> >>> > dark (itself) at parts close to other geometry. Should AO not have
>> much
>> >>> > less impact on such surfaces? Otherwise it can be hardly combined
>> with
>> >>> > transparent materials.
>> >>> >
>> >>> > Do you see room for improvement or should it stay this way?
>> >>> >
>> >>> > Greetings from
>> >>> > Tobias Oelgarte
>> >>> > _______________________________________________
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>> >>
>> >>
>> >>
>> >> --
>> >> ____________________
>> >> François Tarlier
>> >> www.francois-tarlier.com
>> >> www.linkedin.com/in/francoistarlier
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>
>
>
> --
> ____________________
> François Tarlier
> www.francois-tarlier.com
> www.linkedin.com/in/francoistarlier
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