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Light Bleeding when using a single floor for many rooms

Hello everyone,

I'm experimenting with lightmaps and there is one artefact I don't understand. It looks like at some point it doesn't matter how many pixels to put between UV shells or how high the lightmap resolution is - the light bleeds anyway. Not sure whether it's me doing something wrong, a bug or just how lightmaps work so any help will be appreciated.

I've prepared a simple project to showcase the artifact. There are 2 maps in the project:

  1. MAP_Floor_Solid map has the light bleeding at the bottom of the walls. The floor is a mesh with two separated geometry pieces and one UV map that has 2 UV shells snapped to the pixels (one UV shell per geometry piece).

  2. MAP_Floor_Separated is what I'm trying to achieve. There is no bleeding. The floor consists of two separated meshes and each mesh has its own UV map.

It feels like the indirect lighting stops to care about the walls or uv-shells at some point.

The solutions I've found so far:

  1. Use a separate floor per room. This way it's possible to completely remove the light bleeding but the final result is not that good because of a different shading between modular floor pieces. More can be found here: LightingTroubleshootingGuide: Shadow Seams/Shading Differences with Indirect Lighting

  2. Adjust the Lightmass Settings. The most useful parameters are: Static Lighting Level Scale, Indirect Lighting Quality, Indirect Lighting Smoothness. The floor looks great, no seams and shadow differences but it's kind of hit & miss to find balance between good looking shadows and no light leaks. Also it's quite likely that the Lightmass settings has to be adjusted each time adding a new light to a scene because the new light can cause more bleeding.

Is there something else to look at? It would be great to get a robust solution with the solid floor as it's done with the modular geometry.


P.S. The blend & fbx files can be found here: UE4Tests/Assets/Blender.

Product Version: UE 4.16
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asked Aug 01 '17 at 10:57 AM in Rendering

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