Separate light function for different material properties?

Development Rendering
1

I’d like to apply separate light functions to the different components of a light (especially ambient/indirect versus direct/specular/metallic.)
Is there some way of achieving this?
I’ve read this: Light Functions | Unreal Engine Documentation
It seems to indicate that all light emitted by the light is scaled linearly.
If I could build a light function that had a separate map output for each material property, that’d be perfect. Anyone done this?

2

So … I’m alone in this?

3

could you give a use case?

4

One use case is simulated shadowing or occlusion using features other than built-in shadow blockers.
I’d like the light’s contribution to global illumination / ambient to be full, but contribution to diffuse/specular to be shaded.

5

I think that would break it away from the PBR setup that UE4 is going for.

Do you have an example?

6

I think light functions does not affect Lightmass calculations in anyway.

7

I don’t think UE4 is going exclusively for PBR. There are plenty of “stylized” games and examples.

For example: Dimming unseen scenery in “fog of war” views.

8

There is currently no supported way of doing this. Light functions are just applied as an additional shadow term for the light there is no distinction of different light functions for different elements. Would require coding. Not a likely feature to get scheduled by us.

9

Thanks, Ryan!
Is that a “we wouldn’t merge that” or a “patches welcome!” ? :slight_smile:

10

Hard for me to say for sure, but generally pull requests that are very complicated and very niche-market are not approved. In my opinion this would fall under that category but I have been wrong before.