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EVSM, 2 component vs 4 component

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I'm looking for an explanation and/or example of why using 4 components vs 2 components is important for EVSM.  In my limited tests, using 2 component 32 bit gives much nicer results overall vs 4 component 16bit.  Dropping from 4 to 2 components does result in a bit more light-leaking, but it doesn't seem bad in the test scenes I'm looking at.  It's still hugely improved vs straight VSM.  Going down to 16bit however (even 4 components) causes pretty noticeable aliasing, and the required bias seems to result in peter-panning as well.

 

I remember specifically reading a presentation from Ready at Dawn, where they had to fall back to using 16bit for memory reasons on The Order.  Is there a good reason they chose this trade-off, vs dropping down to 2 components?

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That's very helpful, thank you.

 

What kind of values did you end up needing for leak reduction?  Is that a value that you think makes sense to expose to artists per light, or did you get away with a hard-coded global value?

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I usually use around 0.2-0.25. I think it's okay to hard-code it, personally. You can't really go much higher than that without breaking filtering, and the improvement from going lower is pretty small. I prefer not to expose things unless it proves truly necessary, especially if it requires adding additional data that needs to be read per-light on the GPU.

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