Hi,
I have hit a very peculiar lighting rebuild bug. I keep getting the red warning text in game in game about unbuild objects, which seems to be related (I think!) to either the engine having an issue with my small lightmaps and/or staticmesh LODs.
A repro project.
https://dl.dropboxusercontent.com/u/2300830/LightingProblem.zip
Problem: Red text top left about unbuild objects remains after a lighting rebuild. Using 4.6.1. Problem has been reproduced on multiple computers so it is not my PC.
Expectation: Rebuild correctly OR at the very least communicate which meshes are the problem.
Repro:
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Open repro project (4.6.1) and open the level LightingFailsToBuild in the project. Play the level.
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Notice the warning about one unbuild object.
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Rebuild lighting (any quality, using settings as they are).
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Play again.
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Warning is still there.
This repro level is extremely simple. It uses just three staticmeshes and one completely standard stationary light. There are no blueprints, there is absolutely nothing but 3 staticmeshes and a light. This should not fail.
The meshes used in this repro level are used thousands of times across my game. They rebuild fine in 99.99% of the time.
I have 4 levels that display this behaviour, so it is not something local to just one level. It is failing consistently on something unknown.
These levels are about 7000 staticmeshes large each. I have tried everything to try and pinpoint which meshes are the issue but it is hopeless. I managed to fix one of the 4 levels by pure trial and error. The objects that do not build are always the same ones it appears, but finding them is near impossible.
What I tried:
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Ctrl X ctrl V does not fix it
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Setting the light to Static fixes it (weird).
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Copy paste to notepad and analyze the text format → cannot find a property or pattern in why this happens
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If you delete ONE of the three meshes, the error goes away! Makes no sense. It complains about one unbuild object yet deleting any of the three meshes results in the error disappearing.
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Setting Lightmap Override on the middle mesh to 32 fixes it! However when we tried doing this on our real levels we still end up with the error. It may be related to it not liking our 16 res tiny lightmaps in certain very specific scenarios.
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Replacing mesh with another mesh fixes it, but that doesn’t help. We need this mesh + this mesh is used thousands of times elsewhere and appears to work fine.
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I have tried the lighting rebuild statistics, primitive stats etc. I cannot find a pattern or a value in any of it that indicates which mesh is doing this.
I am at loss what more to do other than to manually go through a few ten thousand staticmeshes to find the about 20 unbuild objects we have across our 3 remaining levels.