Chaos Corona Forum

Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: dsolod on 2022-11-29, 12:33:06

Title: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-11-29, 12:33:06
Hello,

The subject and the attached image should be self-explanatory
Is there any way to avoid it?

Thanks,
Dmitry
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: romullus on 2022-11-29, 14:01:24
Are you sure that's GI and not reflection? Did you try to disable reflection on the sphere's material (set IOR to 1,0 for physical, or reflection to 0 for legacy)?
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-11-30, 07:15:34
The image was showing CESSENTIAL_Indirect RE

Disabling the reflection is definitely not the right solution for me. But even with disabled reflection of sphere the CESSENTIAL_Indirect RE looks wrong. Please have the updated render with IOR=1.0 and test scene attached
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: romullus on 2022-11-30, 10:53:24
Sorry, i didn't notice that it's indirect RE. Maybe Corona counts secondary reflection as GI, i don't know. I did similar setup as yours and find that you also need to set roughness to 0 in Corona physical material and then you should get indirect component without reflection influence, or simply use legacy material, which lets you turn off reflection completely. If losing reflection is not an option for you, then maybe consider render twice and compose the final image from render elements? In any case, it would be helpful if you could tell what are you trying to achieve, maybe there are alternative approaches.
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-11-30, 13:16:50
I have the living room with the heavy red colour carpet in it. Obviously, I can't have the ceiling and the walls without reflection
I don't mind to see the red colour in CESSENTIAL_Reflect RE but please not in Indirect one.

If it's not a bug, how can I overcome it keeping the reflection and not rendering twice?
Or is it a bug? Because V-Ray behaves the predicted way
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: romullus on 2022-11-30, 14:14:29
If you have bright red carpet that you don't want to affect rest of the scene, then you can plug red material into rayswitcher's direct override slot and neutral grey material into all the other slots. Would that solve your issue?
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-11-30, 14:39:44
Unfortunately, I have the wall mirrors and glass cabinets reflecting the carpet.

Anyway, for now I will use the suggested solution from you with double rendering. Thank you!

But my main question, is it a bug or intended behaviour? In my opinion, Reflection slot shouldn't affect the GI, similar to VRayOverrideMtl

Hope it will be fixed
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: romullus on 2022-11-30, 14:45:24
Sorry, i can't tell if it's a bug (i suspect it's not), you will have to wait for response of someone from the Corona team.
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: maru on 2022-11-30, 17:09:38
Our team will look into this. I think it may be expected (something like what Romullus said: treating reflections as GI).
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-12-01, 08:28:38
Thank you maru!

Looking forward for fix or feasible workaround of my problem with explanation of this behaviour

Cheers
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: Avi on 2022-12-06, 17:12:44
Hi,

As I have checked the file. The plane seems to be reflecting red color, and the sphere seems to be catching the red reflection from the plane. You can either zero the reflection in your object or make the plane not visible to reflection and refraction so that the red reflection will go away from the object.

Here is a video: https://bit.ly/3BfDsUu
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-12-07, 07:17:03
Hi Avi,
Thank you for your reply and the video
Similar ways were already discussed in this topic before with romullus and that was not the solution for me. So I had to render the interior twice with following post work

And that brought me to the question that I am addressing to Corona Team.
Is it the correct behaviour of the CoronaRaySwitch material?

Again, VRayOverrideMtl works as predicted without interfering the elements

Looking forward for your explanation
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: Avi on 2022-12-12, 15:59:44
Hi,

Thank you for being so patient.

After discussing this issue with our devs, this is confirmed that reflections are considered indirect lighting GI after the ray has been through some glossy/diffuse reflections. I am afraid there is no workaround for this but feel free to let me know how this is blocking you in your project. Maybe we can find some other solutions.


Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-12-14, 08:07:44
Hi Avi,

Thank you for your reply.

Do you consider this behaviour as a bug and should we wait for fix?
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: maru on 2022-12-14, 09:51:39
Hi, I would not consider this a bug. It's just the way Corona works, and I don't think we can expect changes to this any time soon. That would be a huge change to the fundaments of Corona.

Can you explain why exactly this is an issue to you? Is it about composing an image out of render elements?
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: dsolod on 2022-12-14, 13:26:24
Hi Maru!

Sure!

Mostly we work on hospitality projects and most of the views are the restaurants/ballrooms with heavy colour carpets, strong spotlights, mirror walls, etc.
The wallpapers and painted ceilings definitely should have the reflection in their materials

I created the typical environment for you in Corona and it's copy converted in Vray to compare

Hope it will help )
Title: Re: Reflection slot of CoronaRaySwitch material affects GI
Post by: Avi on 2023-01-12, 14:03:44
Hi,

Thank you for sharing more information about your project and the specific use case you are encountering. The Corona renderer is designed to treat reflections as indirect lighting GI after the ray has been through some glossy/diffuse reflections.

In general, it's important to understand that different rendering engines have different ways of calculating light and materials. Corona renderer is known for its physically accurate approach; while this approach does make it more difficult to create certain types of "fakes" or special effects, it also means that your renders will be more true to life and realistic.

Some workaround that we have already shared includes that you can turn off the reflections of the wall if you don't want it to be affected or reflect any other material in the scene or for this specific use case, you can also consider using V-Ray as it supports non-physical effects better.

I hope this helps.