Hair shadow pass setup?

[rray]

Moin,
found some different takes on that aleady but none of them so far did quite work for me.

The idea is simply to have every material display 100% white unless there's a shadow from the hair (or in my case grass) falling on it.

What so far worked best for me is the mia_matteshadow shader that has an output shadow_raw that does exactly that.

The problem I have now is that shadows from other objects are output, too. I could simply turn shadow casting off for those objects, but then I have another problem which is that shadows from the hair that are inside those formerly shadowed areas are being output too --- which would result in double shadows when compositing.

So it seems I would have to have shadows from those other objects rendered white -- I think this would do it but I have no idea how to set this up (in 1 pass), will be grateful for any ideas or input

Cheers,
Ray

[Mathaeus]

Here's yet another recipe, popular in community of another 3d app, when we already with "matte-shadow" name. Characters in that self-or-from-others shadows situation. At least, a lot of dealing with matte keyers in comp. Don't know does it even work with hairs. Max, VRay and Fusion, but should be applicable anywhere.
Link.

[rray]

Thanks. It looks like it would work with hair too. But no "hair-shadow-only" pass, probable need another matte shadow pass to cut out from the hair shadow pass.