Ray discrimination depending which object comes from?

Hi, I’m involved in a project that needs to obtain the light contribution from surrounding objects. To make it simple, think of a empty room with a point light in the middle of the ceiling and a sphere floating at centre of room. We need to obtain only the reflected light from the room, not the direct light nor the default emission this sphere could have.

In a more complex situation, we would need to obtain that light contribution from walls only, so from some certain objects. It could even be possible that some contributing objects may be controlled (its contribution) with emission material parameter.

How could we achieve this? Thanks in advance.

Are you talking about render passes?

Kinda, with ‘Indirect’ I would get what I want but I can’t discriminate the contribution of each object. I mean, I would get the sum of all objects indirect light, not being able to get only the contribution of say floor.

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