How can I add occlusion materials into Reality Composer? Can I add them in Reality Converter? How would I make a portal etc?

Just trying to figure out how to make an occlusion mask in Reality Composer or Reality Converter.

I use Blender to make my assets and want to be able to make something similar to a portal which would require an occlusion mask.

How can I add occlusion materials into Reality Composer? Can I add them in Reality Converter? How would I make a portal etc?
 
 
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