Thanks for ye answers.
Actually this is not about seeing the glass in the alpha channels.
I am referring to the fact of having the selection of a material behind the glass, with the deformation of the refraction, or having the selection of a material in the reflection (glass or mirror).
I have attached an example of an image I just did, I need to have the selection of the wood table in the reflection, and the deformed wood in the refraction of the glass/water.
I hope this is clear!
Thanks for your time