Is Cascaded Shadowmap really so expensive?

Development Asset Creation FX
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1

I tried out a Cascaded Shadowmap in my forest scene with a moderate setting of 10 meters, but that cost me about 20 FPS. Is that really so expensive or is there some trick that I am not aware of? Right now, I can not afford to loose so much speed just for a small optical effect.

Thanks

2

Typically, yes, it is quite expensive, and especially with dense foliage scenes, yet “but that cost me about 20 FPS” gives not enough information to bring out a conclusion.

3

Ok, thank you then. I was just wondering because the standard answer you get from Epic when it comes to large landscape is “use mobile lights and not static” although it looks way worse than static light and also is much slower, so I was wondering if I am doing something wrong or if this advice was simply nonsense

4

Hey Wallenstein,

For large landscapes or larger scenes dynamic lighting makes more sense because even though dynamic lighting is expensive you don’t get the hit to texture memory resources that you would have when hit with static lighting for large scenes. VRAM is finite and depending on the GPU can run out quickly when streaming in a bunch of lightmap textures for a large scene. It cuts into your texture budget. Dynamic lighting does not. This is why it’s suggested to use dynamic lighting for large scenes, similar to what we did with the Kite Demo. The biggest thing with dynamic lighting is to keep your vertex count as low as possible by making use of LODs. Dynamic lights calculate each vertex no matter the size on screen, so you have to be careful because a 10k mesh is just as expensive up close as it is far away for shadow calculation with movable lights.

-Tim

5

I see. Well this seems to make sense then only with open landscapes with few shadows like the Kite Demo.
I have a forest setting with lots of trees close up but they must also be visible to a distance of 2-300 meters in order to give the impression of a claustrophic forest, plus I have some high trees who’s crows basically shade most of the forest except some open spaces here and there. So that would be a big No for dynamic lighting then.
I just thought I could improve the close up shadow with Cascaded Maps but even a short range of 5 or 10 meters drops the FPS drastically there