AccuRender nXt

advanced rendering for AutoCAD

Roy,

I just got done trying to render a model I've been working on. The glass in the rendering was no longer transparent. I found that since the new version of nxt with sub-surface scattering has changed my glass material to have sub-surface scattering and attenuation were set to 20 and 30 cm.

Is this normal or a glitch.

 

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It's a design decision on my part-- probably a bad one.  I used the same translucency and attenuation stuff from before to represent scattering and absorption.  When you switch to the path tracer you can get some results you didn't intend.

 

Those #'s by the way, do not represent 20 and 30 cm.  They represent a probability of a scattering or absorption event occuring per cm.

 

*****

 

I may fix this by starting fresh with the SSS params.  This will screw up anyone who's been playing with the stuff in 255.  Not decided yet.

I didn't switch to the path tracer. I just tried to run a test render with the original rendering engine and noticed all my glass and glazing was very, very dark instead of clear glass. Once I got rid of the subsurface scattering and attenuation it renders fine.

Ah-- I did change the way Absorption (the old Attenuation) works in the Packet Tracer.  You shouldn't have been using that anyway.  I haven't changed the scattering / translucency setting.  I still should probably split these out-- even if it's not what you ran into.  Only one user here (Peter) has been playing with this stuff anyway.

 

What do you mean "I shouldn't have been using that anyway"?

I'm going to have to relearn how to use the settings for glass materials

Attenuation (or absorption) is not particularly useful for architectural glass and probably should never have been set.

I'm having the same issue.

Existing glass materials now have a slight atenuation set which makes them appear opaque. So I have to edit it out before I can render.

I can change the attenuation default units to meters-- that should make existing materials behave better.  It will need to wait for the next build which is still a few days away.  Attenuation shouldn't be used for architectural glass, though.

I think there may be something wrong with the attenuation values anyway.

Take a look at these:

The default sphere is 1 meter across (diameter, I think).  Attenuation means the probability of an absorption event occurring per cm. Change either the units of the Attenuation or the scale of the preview object and you'll see the effect better.

 

I'm proposing changing the default attenuation unit to meters, which should make the thing look pretty similar to before.  This is still a good setting to get rid of in your glass-- it will trigger an SSS calc. which may be costly.

Roy,

I have no way to go back and check now but the glass I speaking of just had a very high intensity with no transparency. The new dialog has added the subsurface scattering on its own.

Yes. Roy has added attenuation in and set the default to 0.2. So it now appears in every material, new and old.

This is fine for small glass objects (set the preview size to 100 and see), but no good for windows and glass partition.

So where is the 0.2 coming from?  There shouldn't be any when you create a new material.  Do some of our stock materials have some?

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