Well, I just want to throw my two cents in here as I’ve been studying UE4’s lighting extensively for almost two years now. Regarding cascaded shadows, UE4 behaves a little strangely under particular circumstances:
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Movable directional might tend to have significantly sharper results than Stationary. Not entirely sure why, but it’s a symptom that also exists with spotlight and point light dynamic shadows as well.
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You can have more than four cascades, but weird artifacts may begin to appear, such as shadows cutting off at a shorter distance, or not rendering at all.
Now, you’re not going to want to get a sharp shadow for grass strictly from shadow cascades because you will murder your performance. I’m also going to assume you’re not using Ray-Tracing. Thankfully, that’s what contact shadows are for, and if you aren’t sure, it’s a parameter in the directional light settings, and the difference can be striking. I typically set the value between 0.01-0.03.
No Shadows
Shadow Cascades Only
Contact Shadows/AO Only
Contact Shadows and Cascades
Hope this helps