Include/exclude shadow casting for particular objects on other objects

[CG_FORM]

Many times while working with V-Ray I wish there is an option to have control on shadow casting by particular object on other objects. For instance: we have 4 objects: all of them cast a shadows. But I don't want object2 to cast shadows on object 4. Now something like this exists in regarding to reflection and refractions, right? Is something like this possible?
Keep Your great work on V-ray!
All the best,
Piotr

[andy51]

Only way I can think of you being able to achieve something like that. would be to have duplicated lights and besides, object properties, cast/recieve shadows and invisible/visible to camera, is part of Max, not Vray and it would be a very messy scene indeed

[CG_FORM]

Only way I can think of you being able to achieve something like that. would be to have duplicated lights and besides, object properties, cast/recieve shadows and invisible/visible to camera, is part of Max, not Vray and it would be a very messy scene indeed

I don't think that will work. I think something like Reflection/Refraction Include/Exclude would work.

[andy51]

I guess what I am trying to figure out, is what situation you might want such behaviour, because I can't think of one.

I can imagine a situation, where say, you have a huge tree, in front of a house, it's not in the camera view, but you want to see it reflected in the windows, but you also want the sun to come from the same angle, which in reality would cast a huge shadow over the building. So you exclude the tree from casting shadows and that cures the problem. My problem is, having an exclude list to prevent it casting shadows only on certain objects would look very weird, say it could cast them on the grass and the fence, but not on the house, it would look as if the house was rendered separately, the composited into the scene.

Come to think of it, maybe Render Elements might be your solution. Of maybe a simpler way would be to render the image with the object casting shadows as usual (master image), then render the object(s) that you don't want a shadow cast on, again, but with the shadow casting object(s) hidden and use photoshop to composite the two. just remember to save the mask (alpha) images as well

[jonnybefree]

sorry to hack this older thread, but i'am in with Piotr. would be quite nice to have a include / exclude list.
i have lots of situations like now. I have a backplate with a tree casting shadows on the ground. now i want to move lets say a ball under the tree passing the shadow. I'am rendering with a matte shadow floor for catching the shadow of the ball. So i place a 3d tree for casting shadows on the ball, but don't want the shadows casted on the floor. I'am rendering the ball and shadows in extra passes for now and hide the tree for the shadow pass, but as we have a lots of scenes its allways double work.
So def +1

[SonyBoy]

I guess what I am trying to figure out, is what situation you might want such behaviour, because I can't think of one.

I can imagine a situation, where say, you have a huge tree, in front of a house, it's not in the camera view, but you want to see it reflected in the windows, but you also want the sun to come from the same angle, which in reality would cast a huge shadow over the building. So you exclude the tree from casting shadows and that cures the problem. My problem is, having an exclude list to prevent it casting shadows only on certain objects would look very weird, say it could cast them on the grass and the fence, but not on the house, it would look as if the house was rendered separately, the composited into the scene.

Come to think of it, maybe Render Elements might be your solution. Of maybe a simpler way would be to render the image with the object casting shadows as usual (master image), then render the object(s) that you don't want a shadow cast on, again, but with the shadow casting object(s) hidden and use photoshop to composite the two. just remember to save the mask (alpha) images as well

There's any number of situations why you'd want this kind of control -- not sure why you're hurting yourself trying to discredit the need for it. Does anyone know if this can be achieved using a Light Path Expression?