Dynamic GI bounces for a flashlight?

Hey guys. I’m looking to find out if there’s an efficient way of creating (or faking) dynamic GI bounces when using a flashlight with the player. I’ve been through numerous posts on the topic of dynamic GI and LPV, and it seems as if you can only use it through a directional light. Apparently using a spotlight for LPV GI provides too much of a hit to performance. I’d love to be able to create it in-game somehow, or at least fake the GI in a way.

As an example of flashlight GI, I looked at The Last of Us, which as far as I know isn’t true dynamic global illumination.


One way to fake it is to do a line trace forward from the flashlight, and if the trace finds a blocking hit you place a low-intensity pointlight at some distance from the blocking surface. A naïve implementation would misbehave in the particular scenario seen in that example image you posted. One would probably have to resort to doing multiple traces in a cone to find the best “average” hitpoint.

Ahem, Lightmaps were used in Last of us for GI
And I can’t see any dynamic GI on your picture or inthe video - it is just simple spotlight + soft point light

Thanks for the replies, guys. Xenome, I’ll give it a shot. We’re gonna run through a few options to see what works best.

Ze0rb, thanks for the links. I’ll need to research this a little further, but it seems like the way to go is point lights (plus spotlight for the cone ofc).

It would probably be a bit technical to add that feature. As far as The Last of Us goes, the game uses lightmaps and then they coded in the feature for the flashlights to have some bounce light.

Yeah in this game they only added DGI to the Flashlight, and even then it’s only enabled in very rare and controlled circumstances (like in the image, when you’ll really notice it).

You could use Light Propagation Volumes for this. They’re not super high-quality but you can decide which lights affect the LPV volumes I believe… it’ll take some setting up. Honestly unless you were going the full DGI route, I’d avoid it entirely and just rely on a soft point light, that casts shadows. The SSR might help ‘fake’ GI a little bit (totally different effect but it can add a lot)

Yeah. The problem with LPV is it doesnt seem to work with spotlights. However, using a spotlight + point light is working marvelously.