Catch shadow hitting glass in Render Element

[Yves Adam]

ok, so here's the thing. I need to somehow catch shadows hitting the glasspane in a render element
to be used as a mask in photoshop.

I have no idea how to accomplish this, I tried almost everything, but I just can't seem to find the lucky combination.
For example, I tried using the VrayExtraTex element, but I can't use an overrideMTL in it, only an override texmap (which isn't the same thing)
i tried using a vray comptex in the extratex, but there's no map that catches shadows.

attached are the render (glass.jpg) the same with an overrideMTL in global switches to see where the shadow would hit the glass (shadow.jpg)
and the desired mask I would want from the RenderElement (mask.jpg).
any help would be greatly appreciated

[Morbid Angel]

if you set the refraction color of the glass to be less then 1, for example 254 (or 0.999) and add matteShadow render element, you will get the shadow as a separate pass on the glass.

[Yves Adam]

That sounded like a solution, but unfortunately, it's not
It would be a solution if I could limit the vrayMatteShadow output to objectID 1 for instance.

just see the output in matte_shadow.jpg ... that's undesired result since the shadowing on the ground appears in it as well.

[Raven]

Maybe try a standard falloff map with light\shadow in the extratex element.

[Yves Adam]

that's not even close to being usable. but thanks for the thought.

I would be helped if I could just tell reflection & refraction which render elements they should affect.
the options now (color, color+alpha, all) are to limited. If I could have refraction affect all EXCEPT VrayShadow then I could/would have my desired result.

[Morbid Angel]

What you are looking for is not possible in vray, or any other renderer that I know. When object is inside refraction any of its elements are no longer considered to be "elements of their own" and they all fall into refraction element. Its not the best. However if you need to do some corrections in post on the specific parts of your scene you would have to split it out and render it in passes.

[Yves Adam]

I was afraid you'd say that ... although when I asked (a while back) it was said that it would
be possible to have refraction & refraction affect elements of coise instead of just color, color=alpha and all ....

that would be my salvation if they implement that. that way, I can have refraction in all passes, except in a rawshadowelement for instance
which i don't use at the moment.

we went from 20 seperate passes/jobs per impression (using black/white material) to 1 (using render elements)
I'd hate to go back to two passes :'(