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Shadow problem at edges

Is it better for Hard Edges to keep the Lightmap UVs ongoing or to seperate them?

In this test-scene is a stationary Directional Light (I wanna have shadowmaps) and 2 static cubes. A cylinder is casting shadows on the cubes. I don't use Autogenerated Lightmap UVs.

One got an ongoing UV-Layout for the important front parts:

alt text

The other got seperated UVs for every face:

alt text

Both are UV-Grid aligned to 64 and their Lightmap UV resolution is 128. Lighting quality is production and these are the Lightmass settings:

alt text

As you can see here, the shadows are individual problematic in both situations :

  1. Ongoing UV's:

alt text

  1. Seperated UV's alt text

Pumping up the lightmap resolution just makes the "errors"smaller... I read many stuff, like of course the documentation, and this here... But i dont understand whats happening :( Especially the offset in the ongoing UV's example is not plausible for me...

Product Version: UE 4.21
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asked Jan 16 '19 at 12:12 PM in Rendering

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SebaSopp
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avatar image SebaSopp Jan 16 '19 at 12:19 PM

Interestingly, with changing the lightmap resolution of the ongoing UV cube to 132 (only +/- 4 steps are possible) the bleeding disappears, but the spreed and offset getting worse...

alt text

alt text

avatar image Jacky Jan 16 '19 at 12:49 PM

I think the errors you are having are partially caused by UV's. The mesh itself looks like a cube with equal edge lengths but not the UV's. I'm guessing you scaled the mesh but didn't remap UV's afterwards. Also you should use power of 2 dimensions for lightmap(and textures too) 4, 16, 32, 128, 1024, etc.

avatar image SebaSopp Jan 16 '19 at 03:11 PM

Hi Jacky. I think unlike with texture UV's it's should not be a problem to have non-uniformly scaled UV shells. As stated in the last section here And the example in the documentation shows it also: alt text

And yeah I was surprised, that its even possible to type in another values then power of 2... I was just curious caused by those two threads: 1 The MOST important thing about lightmaps ! 2 Lightmap Density not matching UVs from Maya

But I must say, that I'm uncertain about how important "UV-Grid Snapping" still is... Those threads are 4 years old...

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