You need to adds lights, while previous version of unreal had emmisive materials that could be source of light, this one does not have due to totally different rendering method. Epic is working hard of getting best things from both rendering worlds but its quite difficult. So i would not count on that unreal 4 ever gets emmisive materials that emit lights, well at least not until we have real global realtime illumination.
Also that emmisive material that made light was always static. ie. you could not change color or intensity of light in game, it was just baked in lightmaps.
So you need to use point lights to simulate that effect. And if i am not mistaken they need to be dynamic, and that is quite challenging because you should not have more than 4 lights in lighting same object, or everything will slow to crawl even on GTX 980ti.
My idea how i would try to make it (i did only static version of your idea, so i did not look at overlaping lights, because all was calculated in editor anyway and baked into lightmaps):
- make blueprint for single hexagonal tile.
- add invisible collision over it. this can be capsule, sphere, or you can make hexagonal tube of same dimensions as tile.
- add event overlap to that collision actor
- change light on begin overlap, and end overlap
- add some neutral static light that imitates idle lighting of tile. Make this one either white or same color as dynamic light. Color from this light can come from floor tile material color.
- and add dynamic light that is changed from overlap events.If you do not need some smooth changes for light i suggest here turning that light visibility on and off (i thin that is cheapest way to do it).
Edit i just read your effect idea:
This will be hard to do, all because of gpu bad performance with multiple dynamic overlaping lights. For limiting that overlaping you may look into light settings there are ligt chanels, but Epic is just implementing them again (they were in engine since ut3, but didnt make yet into ue4 fully). When lightchanels work you could do 3 or so and assigne them to tiles to minimize overlaping of same chanel lights.
Now some links (and search engine keywords, add “unreal” to them) that you should look into:
“dynamic instanced materials”: Instanced Materials | Unreal Engine Documentation
“material parameter collection”: Material Parameter Collections | Unreal Engine Documentation
“material functions”: Material Functions | Unreal Engine Documentation
for blueprints:
“interpto” The Subtle Magic of InterpTo() - Unreal Engine
And there are 2 nodes exactly for what you want with smooth values animation, but sadly i cannot remember names or keywords.