Maxon Cinema 4D Forum
Standard render or physical: Reflections linked to specific objects
Standard render or physical: Reflections linked to specific objects
by Steve Bentley on Dec 11, 2019 at 5:49:17 pm

Is there any way to (like we can with lights) assign a specific object to reflect only in another specific objects polys? So if you had three mirrors, you could have a ball in the scene assigned to the middle mirror where it would show in the reflection but it wouldn't show in the reflection of the other two mirrors?
This seems like a viable and reasonable extension to the compositing tag.
Is there a way with expresso and a link list perhaps?
I can get er done of course with multiple renders but I'd rather avoid that. We do a lot of product shots where you use reflectors to make it things look sexy. But you don't always want a certain reflector that looks great in one object to show up in another. Eyes in figures really benefit from this - show me that eye reflection hot spot but not the nose, glasses, the other bounce reflectors etc that just complicate the window to the soul's reflections.




Re: Standard render or physical: Reflections linked to specific objects
by Brian Jones on Dec 11, 2019 at 8:54:38 pm

Exclusion tab of the Compositing tag by the description - apply it to the ball in your first example and exclude the mirrors you don't want to see it (or swap it to Inclusion and include only the one you want to see the ball)


Re: Standard render or physical: Reflections linked to specific objects
by Steve Bentley on Dec 11, 2019 at 9:54:14 pm

Slaps forehead. Of course! Thanks Brian. Saving my sanity as usual.




Re: Standard render or physical: Reflections linked to specific objects
by Steve Bentley on Dec 11, 2019 at 10:48:48 pm

Hmmm. Not sure how to think about this. That did work, but only for the first bounce.

Regarding an "odd man out" reflection object (the object that should only be reflected in one object instead of all objects): Any object that is included in the exceptions list to receive the reflection will also lend the odd man out reflection to other objects even though other objects are not included in the in the exceptions list. So the other objects can't see the reflection of the odd man out object directly, but do see it indirectly through the reflection of the object that can see the odd man out reflection.

As well, if you use the pre R16 method of materials (without everything jammed into the Reflectance channel, but using a Beckman et al in the Reflectance channel) and map those materials onto the receiving objects, anything that receives luminance from the odd man out object (whether that receiver is reflective or not), that light will also be reflected in objects that have not been included in the exceptions list, and this will happen on the first bounce as well as subsequent ones.

I guess I figured the traced ray would be tagged with objects it could intersect with - otherwise the system is burning tracing runs when they aren't needed. Why calculate a path to an object the light isn't supposed to be reaching?




Re: Standard render or physical: Reflections linked to specific objects
by Steve Bentley on Dec 13, 2019 at 1:59:13 am

Well so much for that. Using the exclusion tab does seem to work some times but as in this example not always.
This is in R19 (its a legacy project so it has to stay in this rev for now). We're using GI with the standard renderer since the other methods have too high a noise to render time ratio (and we're not liking the after market denoisers for this).
This of course is a simplified scene but all the main players are here.

There are a bunch of GI emitting planes and disks, but at the bottom of the objects list is the "odd man out" emitter. Currently it is set to only affect the small primitive grey sphere in its composting tag exclusion tab. But if you turn the oddManOut emitter off, you can see it is affecting the skin colored sphere. Is the "exclude" option the only one that works in the tag? "Include" doesn't seem to isolate that emitter to only the objects included.

I've even put all the emitters in all the other emitter's compositing tag exclusion tags thinking that they might be lighting each other up and then acting as bounce cards.
But if you turn off the emitter called "eyelight" (which has the same exclusion parameters as OddManOut) it doesn't affect the skin colored object. Inconsistent!

What I'm after here is to add some emitters and reflectors to add little kisses on a much larger and more complex model, but I want to only affect certain objects. But some of the emitters, even with composting tag exclusion sets, are affecting all the objects and not just the one I'm trying to target.

Am I not thinking about this correctly?


13950_balltest.c4d.zip







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