What is Building Light and Why is it necessary?

Hey guys as the title implies, I’d like to know what is Building Light and Why is it necessary?

After dragging in lights from the Modes window whats with this extra step?

Rendering many lights at realtime is extremely costly.

A common performance technique is to render the lights into a lightmap texture that is applied.

Baking lighting is more about getting high quality indirect lighting. Even the best dynamic GI solutions only allow for a few light bounces, and they don’t capture medium or small details very well.

With deferred lighting the number of lights isn’t a huge issue, shadows were though. And since 4.13 with Cached Shadow Maps, shadows aren’t as much of an issue anymore.

So…are you agreeing with him?

It sounds as if you are agreeing but then disagreeing

Having a large number of lights in a scene without using baked lighting is not an issue at all. And baked lighting is about achieving higher quality indirect lighting and shadows, not the number of lights. That’s what I was disagreeing with.

Still there’s performance issues related to shadows that you have to worry about when using a large number of lights.

But then you also said that wasnt a problem anymore ever since 4.13 right?

I don’t want to muddy the waters further…but think there is value in clarifying:

The primary reason baked lighting was originally created was to avoid the costly evaluation of the light equations in the fragment shader during rendering.

Originally most game engines utilized a technique called forward rendering which had a direct linear cost with the number of lights in a scene. Each fragment evaluated each lights contribution. In recent years, Unreal began utilizing deferred rendering, in which the cost of the light scales directly with the number of fragments that it covers. Note, there is still a cost to every light in the scene. (And ironically, VR is driving a push back to a modified forward rendering algorithm often referred to as Forward+)

ZacD was trying to point out that the current rendering engine in UE is so powerful and can easily render many lights and shadows, so that in his opinion the improved quality of light baking was more valuable than the performance benefit and the ability to render more lights.

In summation, light baking can offer better quality and better performance with a few significant caveats. (Like having an offline baking step, and not lighting dynamic(moving) objects).