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# Baking a Local Thickness Map

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### #1Migi0027 (肉コーダ)  Crossbones+   -  Reputation: 4342

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Posted 06 February 2014 - 02:59 AM

Hi guys  .

As you know translucency is a big topic, and can be really expensive to simulate, therefore we prebake certain things, like a 'Local Thickness Map'. Which basically contains the distance from the current point to the one, well, behind, so the thickness, that can be locally mapped on a mesh, like this one:

=>

The technique described by the paper by dice (

The offline approach described by the paper reads as following:

To streamline this, we rely on a normal-inverted computation of Ambient Occlusion
(AO), which can be done offline (using your favorite modeling and rendering software)
and stored in a texture. Since ambient occlusion determines how much environmental
light arrives at a surface point, we use this information for the inside of the shape (since
we flipped the normals), and basically averages all light transport happening inside the
shape.


Though I'm not fully sure what they exactly mean, are they implying that it's a brute force AO ( raytracing ) with inverted normals?

So my question is really what approaches can I take at baking this map?

You reached the bottom, thanks for your time!

-MIGI0027

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### #2Chris_F  Members   -  Reputation: 3018

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Posted 06 February 2014 - 03:41 AM

Though I'm not fully sure what they exactly mean, are they implying that it's a brute force AO ( raytracing ) with inverted normals?

You are calculating AO, but from and to the interior surface. The occlusion value is then inverted to get the local thickness value.

Edited by Chris_F, 06 February 2014 - 03:42 AM.

### #3Reitano  Members   -  Reputation: 690

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Posted 06 February 2014 - 04:37 AM

I did some research on this topic recently and apparently the latest version of xnormal has support for baking translucency maps.  I haven't tried it yet and I'd be curious to see what results you'll achieve in your implementation.

### #4eppo  Crossbones+   -  Reputation: 4471

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Posted 06 February 2014 - 08:22 AM

Tried this out in Modo. Simply flip the polygons and bake an AO map.

Edited by eppo, 06 February 2014 - 08:37 AM.

### #5Tocs  Members   -  Reputation: 689

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Posted 20 February 2014 - 03:16 PM

I know this topic is 14 days old but I started working on the subsurface scattering that uses these maps and needed a way to generate them. I found XNormal has a built in option for this type of map. It's called "Translucency" and not "Local Thickness". You won't need to flip your normals and such. It also has a C++ library if you want to integrate baking into some sort of tool you're building, and it's free.

Edit: Here's the translucency map generated from XNormal used in the shader...

Edited by Tocs, 20 February 2014 - 04:15 PM.

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