Unreal 4 Lighting Academy....or something like that ;)

[anonymous_user_f2b8b290]

I have been summoned.

The thing is this: “3 lights per object limitation” this one ONLY exists because of the distance field shadowmap that is being generated by the stationary mode. Static lights dont have that, which is the reason static light baked shadows look worse with low lightmnap rez. When turning on area shadows for you stationary light, it actually defaults back to the old shadow baking technique JUST with soft penumbras. So in theory, that should get rid of that 3 lights per object limitation since its not using the same shadowing technique anymore.

The limitation is 4 shadow casting stationary lights affecting any point in space. The directional light consumes one everywhere so you effectively get 3 for point / spot lights.

Static lights bake all their lighting and shadowing into the lightmap so they don’t have any limitation on overlap but they also can’t ever integrate properly with shadowing from movable objects and characters.

Stationary lights bake out their shadowing separately for each light. In the deferred renderer we have to get these shadow factors from the BasePass (where lightmap UVs are available) to the deferred lighting passes so we have to pack the 4 shadow factors into the GBuffer. This is why the limit of 4 exists - to keep the GBuffer small as it’s like a performance tax on the entire deferred renderer. The Forward renderer also has a 4 shadow casting overlap limit, but for slightly different reasons.

So regardless of whether you choose ‘Use Area Shadows for Stationary Light’ or not, we still have to store out shadow factors separately for each stationary light to support combining with dynamic shadowing and the 4 overlap limit is the same.

You wont get any specular from static lights

Technically static light sources are drawn into reflection captures so you do get direct specular from static lights if you have reflection captures setup, but yeah it won’t be anywhere near the quality of Stationary lights, which have correct parallax and are shadowed correctly.

Right now, you cant have a light that can make GI for lightmass, has specular AND it doesnt matter how many you have…so thats clearly something that can be improved.

It is possible to support more than 4 shadow casting stationary lights affecting a single point, but it would add rendering overhead (either another GBuffer, or re-render the scene’s meshes again to output the next 4 shadowmap channels) so we haven’t tackled it yet.