Material ID and Transparency

[valerostudio]

Any tricks on how to get the material id for a 100% clear glass to show up in the VFB? Seems like the materiald id takes the transparency into account.

[andybot]

yeah, I've run into that problem too. I put a plane behind my windows in the interior, set it to a new matID...

[valerostudio]

So you do a separate region render after your beauty pass is done?

[andybot]

erm, no. This is only with an exterior model, so it doesn't matter so much what's on the interior. Don't know any more than that, I've not used material ID for windows where I can see the interior. Maybe a reflection pass can help you mask your windows out?

[thomthom]

Can you render out a pass with transparency disabled...?

[andybot]

@valerostudio: I figured it out! - you don't have a refraction layer do you? It works fine with a refraction layer...

Not to mention - it gets weirder if you have an ID color for the glass - it overlaps the ID color of the other IDs. see second matID map example.

Here are my material settings:

[thomthom]

This smells like bugs all over the place!

[thomthom]

@andybot said:

Note that the amount of transparency is very different with a single layer of glass.

Isn't that the fog?

[andybot]

no, my fog color is pure white. There's two layers of reflection instead of one.

Edit:
Oh, and the dark blue glass is not completely transparent. This is a material I use for exterior renders when I don't want to see in the building.

[andybot]

Buggy, yes, just one of many
c'mon new beta!!

One trick - if you are using a single layer of glass, is to change the refraction IOR to 1.0 to avoid distorting objects behind the glass.
having the refraction layer works with both single and double thickness glass for MatID.

Note that the amount of transparency is very different with a single layer of glass. (Edit: I am using a semi-transparent material for the dark blue glass instead of fully transparent.)

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[valerostudio]

Flipping A! Nice work to finding a trick for this pain in the butt bug. Seriously need this new beta.

[valerostudio]

The AA on the glass id channel does screwy things. Anyone know why this is?

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[valerostudio]

I assume its a product of refraction. You can see the AA on the green edge compared to the red edge of the glass. Choppy and weird. At least this is a decent workaround. Thanks guys.

[gparadis]

Reverse question - is there a way to exclude 100% transparent material from the material ID render ? Say I have a texture of a tree where the foliage is opaque and an alpha channel masks what's not needed. Material ID still considers the transparent surface as a different material.

When a lot of objects are in background, selection is not optimal.

Thanks

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