Octane Light as a Flag

[harrystanper]

Hello, i'd like to use area light's light linking feature to get black reflections instead of white on certain objects. Is this possible?
General visibility 1 and light power 0 gives me kinda what i want but the light leaves unwanted shadows when intersecting other objects even when light linking is on.

[bepeg4d]

Hi,
have a look at the documentation here:
https://docs.otoy.com/cinema4d/Workingw ... nking.html

ciao,
Beppe

[frankmci]

You have to capitalize that C and D in Cinema4D or you'll get a 404.
https://docs.otoy.com/Cinema4D/Workingw ... nking.html

[jayroth2020]

Yeah, sorry about that guys. New version of the docs is up, but we are waiting on a redirect to address this issue before we make the announcement.

[harrystanper]

I've read that already. Could you refer to specific paragraph?
Still don't get why i get shadows from the light source on object B when light linking includes only object A.
Other renderers don't have it.

Could you take a look at my test scene? I highlighted the problem area on a rendering.
https://drive.google.com/drive/folders/ ... sp=sharing

[bepeg4d]

Hi harrystanper,
the scene is full of Arnold Render elements, please avoid to mix c4doctane Render Setings, with any other render engine settings, or you could have crashes:

You are also using a JPG image in Environment Texture node for lighting, this is not the best, better to use .EXR/.HDR 32 bit images for lighting:

Here is the scene with Octane materials, and Octane Object Tag assigned to the Disk geometry:

Test. Light Linking_b.zip

(195.53 KiB) Downloaded 48 times

ciao,
Beppe

[harrystanper]

Thanks for response. Yeah, Light's Opacity set to 0 solves my problem when Light's Intensity > 0,
another thing i'd like to resolve is using a light as flag (the same setup, but Light Intensity: 0 to provide black reflections).

Take a look at "Test. Light Linking C.c4d", is there a way to save a black reflection and eliminate shadows on Disk object. Thanks.

https://drive.google.com/drive/folders/ ... sp=sharing

[frankmci]

another thing i'd like to resolve is using a light as flag (the same setup, but Light Intensity: 0 to provide black reflections).

If I understand you correctly, you can also use Ray Switch to make a geometry flag object visible only in reflections.

Reflections Only Flag using Ray Switch node

If using a light object for the same purpose, it blocks ambient light, even with Shadow Visibility off. That may not be a problem most of the time, but if it is, the Ray Switch option works fine.

Black Light as Reflection Flag

[harrystanper]

Yeah you've got the idea! Ray Switch with geo did exactly what i wanted, but isn't there a way to make it work for lights?
I really want to use Light Linking feature.

[frankmci]

Yeah you've got the idea! Ray Switch with geo did exactly what i wanted, but isn't there a way to make it work for lights?
I really want to use Light Linking feature.

My second example above was made using lights. It works, but there's the small problem with the Light Object blocking ambient light, even with Camera Visibility and Shadow Visibility turned off in the Visibility tab. For the Light Flag to be visible in the reflections, it has to have the General Visibility turned up, which impacts ambient lighting. If you look at the round base, you can see the ambient occlusion where the light object is closest to the surface. That's really only a problem if the light object needs to be relatively close to another object where it will noticeably reduce ambient lighting.

Later...
Oh, ok, I see what you mean. I hadn't actually tried it with light linking. Light linking will hide or show the illumination from the light object in that lighting group, but doesn't control the visibility of that object in reflections. I'm afraid I don't have a solution off the top of my head. I'll stick it in my ponder box and let you know if I think of anything.