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did you think it s possible to have mask behinde glass
whith custom alpha channel
verry important for our production
thank very much for your help

Use AGS material as glass in that case you can see object ID or material ID

it s for a very hi level of render image
i can t use AGS for this client
thank

Maybe use an annotated photo to explain what you're exactly after.

Maybe I'm not understanding the question but can't you do this with a simple layer material?

He wants to get an alpha of the objects behind a glass object with the refraction effect.

Seems like your client wants some magic )

Back in the days, before we had Object IDs we would use simple surface shader with flat colour (read emitter in Maxwell). So basically if you would make another render making your object behind the glass shaded as a flat colour (bright red would do) you could easily isolate it with all it's refractions - since its a simple flat colour. And if you would pick one of the three primary tones - you could even do that automatically with shifting channels in pretty much any compositing app.

I know, a bit of an old school approach, but if your client want's magic and you don't want to involve programmers - that's the easiest way to do it. Should also work on sequences
Cheers.

Thank you Nasok. That's the way they do at the moment, but as this feature exists for other render engines it could be added to our favorite renderer too.