Cycles Light and Shadow Linking

This is a topic for feedback on the new light and shadow linking support. It is available in daily 4.0 builds.

Please read the release notes, and report any bugs in the tracker.

A detailed overview of planned improvements is in the issue on projects.blender.org.

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I tested the latest build of light linking and I noticed that it disables the emission of a material if it’s used as a light to be linked to something else.

In the attached image I selected this green mesh light, added a cube as a light link and it automatically disabled the light from the mesh. Is this a bug or intentional?

Is it possible to keep the mesh light on while it only lights the cube?

Thank you for working on this!

Some initial thought and suggestion regarding UI/UX.

  1. I think data block eyedropper at the linking panels would be useful so users can quickly add receivers from the panel.

  2. Link operators exposed in other renderers? - Link operators in Link Data menu are exposed even if the render engine is not set to Cycles. I imagine Eevee will get light linking eventually but I doubt Workbench will get one, and there are external renderers. Not a big deal but I think it can be little confusing or misleading.

  3. Link operators in Link Data does not stop you from trying to link objects that are not valid for light linking. For example mesh to camera, camera to empty. It creates a collection still, making redundant data.

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Thanks for your work on this!

Some initial thoughts and suggestions on UI/UX.

1: Is adding objects to the light link now the opposite of the shadow link logic?

2: Personally, I think the UI setup in the last version was a bit more in line, this version is not very intuitive.

3: The effect of adding objects to the excluded folder of the light link is not updated in real time, you have to select the excluded folder again, or there is a real time effect but as soon as you move the objects in the collection the link effect will be invalid.

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It’s a bug, fixed now.

We planned to add a (+) button that would add selected objects. An eyedropper would be possible too, but maybe selection is more powerful as you can use all selection tools.

Fixed now.

Fixed also.

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I’m not sure what you mean. The way it works is that for a light object, you can assign which objects receive light (light linking) and which objects cast shadows for that light (shadow linking).

I’m not sure which version you are referring to.

Some refresh issues were fixed today, but it’s not clear to me if that is what you are referring to.

In general I would not recommend using a scene collection directly as in your screenshot, but rather create a new one and put objects or collections in that.

Hi Brecht,

Thank you for all your hard work! I have a question that I’m hoping will be addressed with light linking eventually.

I render a lot of glossy jewelry and sometimes if they’re grouped too close together I get a lot of unwanted indirect glossy reflections. I’ve used Photoshop and render layers/compositor to get rid of these reflections, see attached, but it takes a lot of time to do. Would be possible to exclude indirect lighting or reflections/shadows from a selection of objects with light linking or some type of ‘object linking’?

Thanks!

That’s called trace sets in other renderers. We don’t immediately have plans to work on that, at least not part of this light linking feature.

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I’ve made a bug report for an issue when you “recursively” light link objects.
Basically, if you link a light to an object, then link that object to another object, the original light link breaks.

Here’s the bug report:

Here’s a video of the issue:
https://projects.blender.org/attachments/ea701721-7038-46f5-90f4-eba6fd5ea02c

It appears that light linking or shadow linking an object against itself doesn’t work. I’m not sure if this is a bug or intended.

An example of when you might want to do this is if an object/character contains multiple materials (at least one of which is emissive) and you want to light or shadow link the object to itself.

Bug report:

Video:
https://projects.blender.org/attachments/6eb210e1-7a87-4777-94e1-9e93dda2b18f

From my testing using Blender 4.0.0 Alpha Hash 0a004fbad460

I tried to light and shadow link only for “Chars” collection.

However, I wasn’t able to link the light using Sun light, but was able to link for other lights ( Area, Point & Spot )

Is this bug or is this known issue ?
I couldn’t find it in the tracker whether this is known issue or not




Light linking is working with the sun lamp. It’s just that direct light sampling isn’t working properly for the sun lamp with light linking resulting in a massive increase in noise. This is a bug. Please make a bug report about it.

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Thanks! Reported here #108374 - Sun light linking issue on direct sampling - blender - Blender Projects

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Actually, it turns out I was slightly wrong. The direct light sampling isn’t working properly for the sun lamp with light linking AND light trees enabled.

If you turn off light trees, things work fine.

what are the use cases for shadow linking?

First of all, compliments to the devs for working on this!!!
I was wondering, considering it is mentioned, how much the devs are planning to change the UI/UX?
Because in my opinion the way this feature is implemented is somewhat unintuitive to work with. The fact that the menu/list for controlling lights and objects globally is inside a submenu of every object, and creating a collection for it, feels confusing. In my opinion we should have a dedicated editor for globally controlling lights and shadow inclusions and exclusions.

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Sergey committed fixes for the issues reported by @Alaska and @Bintang.

@Hari_Abburu and @slowk1d, please check the links in the first post in this topic, the release notes and issue cover this.

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thanks brecht for the info!

The fact that it’s relying on collections to build the relationships doesn’t seem optimal, as now it’s going to require the user to structure groups and hierarchies in ways that may be rather inconvenient with other collection requirements of the scene.

The user wants an object to only contribute a shadow, and nothing else.

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You can link individual objects too, there is no requirement to use scene collections. Did you try using for example Ctrl+L for light linking in the 3D viewport?

I’d still recommend using collections when possible, so that you can add and remove objects without having to update the light linking each time. For example if you have an environment collection linked from another .blend file, being able to add an object to the environment without having to update each shot file seems convenient.

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