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Cast shadows look like blobs. What could be the cause?

Me and my friend are diving into UE4 together with me as the technical person, and her as the artist. When placing down trees in our level, we run into a problem (both using UE 4.10.4). We have done maybe 6 hours of online research with no useful results thus far.
problemlightmap density
This problem occurs only with the trees in the level, and only first appeared once a few thousand faces worth of meshes had been placed. They all look and work very similarly, so I'm showing the one that claims to have 88.0% overlapping.

This blob of a shadow does not change when I increase the Lightmap Minimum Resolution, change skylights or directional lights to Static or Stationary, or change any other seemingly related setting.

This is the UV layout for the tree's texture. All of the sets of leaves are stacked on top of each other.

lightmap uv
This is UE4's auto-generated lightmap UV, which, as disproportional as it looks, has no overlapping.

  • Upon seeing "overlapping," I thought it must be the texture UV that was the problem, but it seemed counter-intuitive in terms of quality, size, and effort. Bushes currently in the same level with similar UV layouts also experience no errors

  • One thing I thought may be a problem was that the trees' materials are set as "Double-sided Foliage." I don't know how this would interfere, but my first instinct upon making this tree was to make the body and the leaves separate. The only other things with that setting are bushes, which are unconnected clusters of 2-d faces.

  • While doing research online, we both found many people saying "never use the auto-generated lightmap UVs," for a reason we don't know.

  • We also found people saying you could use dynamic shadows if baked shadows weren't working. Being relatively new to UE4, I tried making the tree Movable, but that just removed all shadows from it and the ground entirely.

Any feedback would be appreciated. I want to make rearranging the UV layout or making my own lightmap a last resort, but I would be willing to do so if that is the only known way of fixing this.

Product Version: UE older version
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error-log.jpg (59.3 kB)
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lightmap-uv.jpg (80.1 kB)
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asked Jul 17 '18 at 08:03 PM in Using UE4

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Hey, I'll be just wild guessing here, but this could be because UE is trying to compute shadows based on the geometry, rather than texture (your leaves are textures on quads as is common I assume).

Try looking here: https://answers.unrealengine.com/questions/487507/how-to-make-tree-shadows-with-leaves-alpha-also-sh.html or


Or try looking into translucent shadows (that's used more for colored glass and some such but it could give you some pointers still)

Also UE 4.10 is a relatively old version, if this doesn't help, you could always try to upgrade to a newer version that tends to offer improvements with rendering. Hope it helps some.

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answered Jul 17 '18 at 10:48 PM

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avatar image femortix Jul 18 '18 at 07:48 PM

Hi, thanks for replying. We did some various testing, and the trees act the same only in the one level, but being in a new level makes their shadows look like the ones in your first link to an extent. Unfortunately, neither of the links' advice seemed to help. For whatever reason, starter content appears to have the same problem as well, even with no default lights or settings being changed.
treestarter content

4.10 is fairly old, and I do assume problems come with it. I tried downloading 4.19, but that version crashed on startup for me. I don't know if there are any known problems like that or if other versions would work, but I can give it a try.

UPDATE: I managed to get 4.19.2 to work, but sadly not the lighting. The shadows look perfect in the previews now, just not the landscape.

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