When using forward shading in 4.17, only a single directional light can be active, all other directional do not affect the scene. I haven’t seen this mentioned as a limitation at Forward Shading Renderer | Unreal Engine Documentation, is it a bug?
It is easily reproducible: create a new project, switch it to forward shading and add two or more directional lights to a map. Only the the most recently added light will affect the scene.
I’m seeing this as well and saw no mention of it either. I’ve taken the terrible approach of replicating the effect of the other directional lights by doing the lighting calculations in my shaders and routing the result to the emission color.
I’ve just tested with 4.18, the issue is still present.
Hello!
Thank you for this information! While this does seem to be an issue, Forward Rendering is still an experimental feature and there are still limitations for its implementation. Using multiple Directional Lights is very costly for rendering the scene in this situation.Thanks again for your bug report.
All the best,