matte objects and double shadows

[Nickh]

Hi,

I have a scene which I need to render in 2 passes. One inside a building, one for characters.

The building is set to be a matte object in vray properties, direct light and Affect alpha are checked.

There is one direct light in the scene which is casting a shadow internally.

When I render the people out they cast a shadow wherever they are, even in the non direct light areas.

I thought that checking the shadows option in the direct light group of vray properties would stop this.

Am I wrong? Is there a way of having them only cast a shadow in direct light?

Thanks
Nick

[panthon]

I have the same problem and it´s very annoying.

[Nickh]

glad it's not just me, kind of

hopefully someone out there will have some top tips

[meanadam]

Not sure I understand here - but why not exlcude shadow casting in the light setting on the people group?

[Nickh]

because then they will never cast a shadow, even if in direct light.

this will work if the people never go into a direct light area, but if they are walking about, in between areas it looks funny - they have a big sunlight shadow all the time.

[Morbid Angel]

it would help if you could show a simple example.

[Sushidelic]

I am aware of the problem as you describe it. The only way to solve it right now is to render out in even more different passes:

1: classic BG pass as you 're doing it right now
2: people's pass without matted shadows, but with all other occluding geometry set to matte alpha -1, shadows affect alpha unchecked
3: a shadow pass for the people with the people set to invisible to camera, the rest of the scene to matte alpha -1, cast shadows off, shadows affect alpha on
4: A shadow occlusion pass, that means your whole set without people as matte alpha -1, but with shadows affect alpha checked (this will output a shadowlayer for your whole scene).

now use your BG as the first layer, then put a layer on top that consists of a composite of pass 3 and 4 - you'll have to invert your scene shadow alpha and use multiply (or darken, depends..) as blending mode for the information in both alphas, like this you'll only keep the people's shadows where no other shadows are.
Last thing is to put your people on top.

I know this is kind of a hassle, but i used this method quite often and succesfully, so if you're on a deadline, give it a try.
Probably the mattes have to be set a little different to what i said above depending on your scene, but if you get the idea what you're really doing, you'll figure that out

I'd be really glad if Vray mattes could do this on their own soon, any news appreciated!

Best regards, Michael

[Nickh]

Thanks, Michael. I'll give that a go.

But agree with you, seems quite long winded...would be nice to do it 1 pass

cheers
Nick

[unknown]

ive just had that very same problem. would be nice if vray caught up on pass rendering. Its the only thing that lets in down as a major production renderer.

[Sushidelic]

Hi! Just edited my above post because i forgot to mention a very important point: You"ll have to invert the alpha of your scene shadow occlusion first before multiplying... If not you'll just keep your people's shadows on the shadow areas of your scene

Sorry about that.

[panthon]

Nice workaround sushidelic!

I was struggling with it a while ago and i gave up. I agree with those who think it should be easier to setup though.
Do u think it could be done by using the information stored on the gbuffer channels, eg the shadow pass as a mask layer?

[Sushidelic]

That would be an idea... I've not been that deep into Vray gbuffers, except Z and Velocity. Really something to find out as this would indeed save a lot of work and extra setup - not to mention, that the workaround gets difficult when you have a lot of glass or opacity mapped stuff in your scene, so that you can't simply use the override material to speed things up etc etc.

Regards,
Michael

[muzzy]

Sushidelic

Nice work around Thanks but vray must have a simple and better way to work around this.