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How to connect ambient occlusion texture with principled BSDF?

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    $\begingroup$ Could you better explain what you mean by "connect" What effect you would like to achieve? $\endgroup$ – Carlo Feb 18 '18 at 22:08
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    $\begingroup$ Without knowing all the sufficient information, the only correct answer would be: There is no need for Ambient Occlusion in the Principled Shader, because it defines the material and not the object's interaction with light. $\endgroup$ – metaphor_set Feb 18 '18 at 22:28
  • $\begingroup$ ...as any other texture? AO is a "world" shadowing fearure, and it can be baked to an image. Use that image as any other texture. $\endgroup$ – m.ardito Feb 19 '18 at 9:25
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You don't connect it at all. The lack of an AO input on Cycles' Principled BSDF node is not an oversight. See my answer here about what AO is and is not for: Adding Ambient Occlusion to Material

Ambient occlusion is so-named because it is occlusion for an "ambient" light type. Cycles does not really have an ambient light, at least not one that accepts pre-cache occlusion data. (the world AO effect is technically an ambient lamp, but it is the only one, and as of 2.79 it always samples its own occlusion on the fly, never from a texture). Since there is no ambient light, shaders have no need to define shading for it.

If you want to use AO data for mesh-dependent texturing effects, you should do these while authoring the texture, that way you do not need to load a separate AO map at render time.

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  • $\begingroup$ Still useful for effects in procedural textures, though, especially in NPR.. but then, you probably wouldn't be using the Principled Shader $\endgroup$ – Robin Betts Mar 28 at 18:19
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enter image description here

Use this node setup, setting up AO in principled is the same as any other node.

The AO in this node setup basically does two things:-

  1. Determines the colour of the AO. As you can see the color of the AO is plugged into the Mix RGB node. I additionally added a color ramp to intensify the AO effect.

  2. Determines the distribution. In this node setup the Alpha of the AO is used to determine the distribution, as the AO is being Overlayed on the diffuse texture. Similarly, you can use the AO texture to control the distribution of other additional shaders or just use it directly.

Blendfile:-

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    $\begingroup$ This is not how you use AO. AO is AMBIENT occlusion. There is no ambient light, and thus you don't need occlusion for it. If you want to overlay your AO on diffuse as a texturing effect, that's one thing, but there's no reason to do it in-shader in this case. Pre-combine them in an image editor so you only need to load 1 map. $\endgroup$ – JtheNinja Mar 21 '18 at 16:53
  • $\begingroup$ OP's question was "How to connect ambient occlusion texture". The other texture was for example only. $\endgroup$ – Retrax Mar 21 '18 at 16:57

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