shadow matte object alpha + displacement

[s0real]

hopefully this will be an easy one for someone. tried a few searches but i couldn't find anything. maybe it's just a setting i've not applied on the vray properties for the object?

i have some objects i'm comping into a photo background. my shadow catcher planes have displacement to replicate the rough surface of the wall and floor, but the shadow from the displacement doesn't seem to cast shadow onto itself if that makes sense?

[fixeighted]

It appears that it works if you use a wrapper material instead of the Vray properties method.

[garipodelu]

@s0real Could it be a shadow bias issue? What is your current value?

[fixeighted]

Not a bias thing...these examples look at each method...

[hermit.crab]

...the shadow from the displacement doesn't seem to cast shadow onto itself if that makes sense?

I think disabling the "No GI on other Mattes" should do exactly that.

It appears that it works if you use a wrapper material instead of the Vray properties method.

I'm getting identical results. Maybe you forgot to apply the base material to the object when you were rendering the object properties matte?

[fixeighted]

I notice that with the wrapper, 'no GI on other mattes' is unticked as default, so it just worked,
whereas it is ticked as default via properties, so I overlooked that

[s0real]

thanks for the replies - just working through things now.

i have remade the shadow catcher object, and remade the catcher material + applied a wrapper, even merged into a fresh scene in case i'd done something wrong early on.

it seems to work maybe a bit better using the wrapper (at least i can make changes now and preview in interactive mode!)

as soon as i increase the displacement value, the issue re-occurs. it's as if the shadow is self-occluding or something?

[s0real]

this is the displaced shadow catcher without the wrapper

[fixeighted]

You need to un-tick the box that says 'No GI on other mattes'

[s0real]

this is with no GI unticked.

[fixeighted]

Maybe something else is going on...posting a stripped scene may help solve it.

[s0real]

OK - simple test scene that replicates the issue attached
It might be that it's behaving as expected?
I've fixed in post for now, but it would be good to know if i'm doing something wrong.

Thanks!

[fixeighted]

I agree; the result is not what you'd expect, after testing this.
It seems like the matte cannot account for self-shadowing, so the result is just wrong and so maybe it's not achievable right now.
I do seem to remember a post a few years ago that noted the same, or a very similar issue.
I'll try to find it in the morning but for now maybe hermit.crab has an explanation or fix if ithere is one

[vlado]

While somewhat unexpected, this seems to work as intended - the shadows of a matte object on itself are not matte shadows - the background plate is supposed to incorporate them already. I verified that similar results are obtained in Corona and Arnold.

Best regards,
Vlado

[s0real]

ok, thanks for testing and confirming my results.