Creating Light Links

Light links are associations between light sources and mesh instances within a scene. They define which lights should and should not apply to which instances.

Light links can only be created during the process of setting up a scene. They are not maintained as individual objects within the scene, but rather extend the data maintained for the light source or mesh instance that they are applied to.

Light-centric or instance-centric

You can set up light links on either a light source or on an instance. If you set up light links on a light, you can identify multiple instances that light should or should not apply to. Conversely, if you set up light links on an instance, you can identify multiple lights that should or should not apply to that instance.

To set up a light-centric link, call the ILBAddLightLightLinks() function.
To set up an instance-centric link, call the ILBAddInstanceLightLinks() function.

Inclusive or exclusive

Each time you add a list of light links, you have to specify whether the links are inclusive or exclusive by providing an element from the ILBLightLinkMode enumeration.

When a link from a light to a list of instances is inclusive, it means that the light will apply only to those linked instances. The light will not apply to any other instances.
When a link from a light to a list of instances is exclusive, it means that the light will not apply to those linked instances, but only to other instances.
When a link from an instance to a list of light sources is inclusive, it means that the instance will be affected only by those linked lights. Other lights in the scene will not apply to the instance.
When a link from an instance to a list of light sources is exclusive, it means that the instance will not be affected by those linked lights. Other lights in the scene will apply to the instance normally.

Each light source or instance can have either inclusive light links or exclusive light links, but not both at the same time.

Handling conflicts

Sometimes, two or more light links may conflict. For example, an exclusive light link on an instance could prevent a light source from applying to that instance, but an inclusive light link on the light could specify that it should apply to that instance. If such a case arises, the light link set up on the light source takes precedence over the light link set up on the instance.

To avoid this situation, consider using only light-centric links, or only instance-centric links.