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New: Added support for Landscape grass to use the landscape’s static light/shadow maps through the “Use Landscape Lightmap” setting in the Landscape Grass Type. This doesn’t look quite as good as dynamic lighting and shadowing, but it is much much cheaper.
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I don’t get the last part? Whole point of this is to use existing landscape lightmaps instead of single probe per landscape grass chunk. It’s has nothing to do dynamic vs static lighting. This is how bad it looked. Grass shading bug. - Rendering - Epic Developer Community Forums
New system is perfect but that patch note is just bogus.