Lighting build taking ages and another weird issue


I hope this is the right place for this. I seem to be having a couple of issues with my scene concerning the lighting. I’m trying to put together a simple wild west scene to showcase a character I’ve made. I bought the assets from the UE Marketplace and some others have been downloaded for free from Megascans. A lot of the buildings won’t be seen much as they’re purely for background/filler purposes. The problem is, even though there’s not an awful lot of stuff in the scene, it takes ages for the lighting to re-build every time. :-\ It came with a Lightmass Importance Volume anyway, but I’ve deleted that and added my own for the area that will be rendered. Also, I’ve checked the Lightmap Density and set a lot of the stuff that was in the red down to default values, so everything’s practically in the green and blue. There are some tables and chairs that are in the orange, which I might adjust too as they’re not going to be seen.

My character was in the red initially as I had to increase the Lightmap Resolution due to weird seams showing on the arms. I’ll probably need to increase it again. Despite all of those changes, the speed of rebuilding the lighting hasn’t improved from what I can tell. I also removed all the foliage in the scene. I was just wondering if anyone can offer any other advice that might help. Or some things I should check etc. :slight_smile:

I also have another problem that wasn’t an issue to begin with, but now won’t stop. Every time the lighting is rebuilt, the barn model I have keeps going black.

A video I saw showed the person setting the Lightmaps to default, though from what I’ve already checked, they are. They’re not very high. Also, there are UVs. Textures display correctly. They’re set up a bit weird, mind. As I say, things were fine before, so I’m not sure why it’s started doing it. I even tried deleting everything to do with it and re-import it back in.

If it’s any use, I’m using Unreal Editor version 4.26

And finally, after the lighting was rebuilt just, it said some of the Lightmaps for my character are overlapping. Is this because of my regular UV unwraps where I have some overlayed rather than offset…? I’m guessing not if Lightmaps are separate UVs…?


You didn’t tell us how long. For this scene, I’d say around 2 mins on a mid range machine?

The lightmaps are in channel 1 and should look like UVs. If they look like rubbish, you can remake them using the static mesh editor.

You often get errors about overlapping lightmaps. The error is related to the lightmap, not the UV. As long as you know the lightmap is ok, it’s probably fine.

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Oh, sorry. I’d say around 10 minutes or so…? I think the log said something along those lines. My PC isn’t modern, but it’s still no slouch. But it’s mid-range. I’ll take a look into the Static Mesh Editor and the Lightmap UVs though. Thanks.

EDIT: As to the barn mesh where it goes black - after building the lighting, it says Object has wrapping UVs.

Building lighting is slow, very slow. Especially if you’re using CPU Lightmass. For medium size scenes you can expect many hours of build time unless you can distribute the workload across multiple computers on your network.

The lightmap UVs should look sensible. So like material UVs basically.

Pop up a picture here, if you want, channel 1:

See how the lightmap for the default cube make sense. What do you have for the barn?

I wouldn’t say my scene is overly complex though. I’ve seen much denser scenes with a lot more going on. :-\ I might have to try deleting the props in the building interiors and see if that helps.

I’ve tried copying the UVs in Max/Maya and adding a new UV Channel. Then, I got it to reorganise them so nothing would be overlapping. Despite that though, it’s still complaining about overlapping UVs. :-\ The UVs for each piece are quite unusual from what I’ve seen before - I think they’ve been set this way for the purpose of tiling textures…?

And then the second channel I’ve set up, I’ve got it to Normalise/Scale everything:

My point is that 10 minutes is virtually nothing and you should be expecting lighting builds to take a lot of time. This is why Unreal has various bake quality modes, “preview” will take the least amount of time while “production” will take the longest.

The static level lighting scale and indirect lighting quality settings will also have a huge impact on your build times.

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Another thing, is it a good idea to have all of my character’s parts attached together? I’m guessing it is as it’s kinda needed for skinning/rigging everything together. But when I see the entire mesh in Max/Maya or Unreal, all the UVs are overlayed like this:

I just hope this isn’t affecting the light baking negatively. It’s complaining about my character having overlayed UVs too. I offset things like one of the eyes and the opposite hands/fingers, but it’s still complaining.

Can you show us the UV channel 1 in the engine

It doesn’t matter what you had in Maya :slight_smile:

Okay. Well, I have Channel 0 and 1. Zero looks like this:

I’ve also added that barn and my character into a new empty scene, so the light building will be quicker whilst trying to troubleshoot them. :slight_smile:

Is there any way of being able to zoom out of that UV view? It looks like there’s more to see, but scrolling the mouse wheel just zooms in and out of the mesh.

Sorry to keep whining on. I need channel 1 ! :slight_smile:

Oh, sorry. Here’s Channel 1, which is what I set up in Max/Maya:

It’s looking like my character, except the barn mesh has each piece in a group. This looks like everything’s selected at once.

Right, that’s a rubbish lightmap, sorry to say.

UE can make one for you from the material UV, all you have to do is

Tick the box, if the box is already ticked, just raise the number to 128 or so.

Then save it and rebuild the light :slight_smile:

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That’s okay, it does look like trash. :stuck_out_tongue: I’m just confused as to why in Max, each piece in the group has a second UV set added, where they’ve been automatically arranged in the grid, but if I select all pieces in the group at once, add a UVW Unwrap modifier, and set to channel 2, it shows just one set in the grid, but everything else is tiling upwards to the top, like in post 7.

But I’ll give that a go and see what happens.

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Okay, that’s fixed it for the most part. :smiley: This is what the lightmap looks like now:

The error has disappeared, although the textures look a bit weird, for some reason.

That’s how the textures look in Max, so there’s some weird dark streaks:

Also, are these seams related to the lightmap resolution or is it UV overlapping?


I did try offsetting the UVs as I said, but it doesn’t look to have done anything.

Did you build light?

It’s really hard to tell from here. The material UVs did also look strange, but you have to build them in Maya. No, it shouldn’t have dark splotches on it. Is Nanite turned off?

You can’t have a lightmap for the player, because presumably they’re going to move, which means you can’t build lighting for them.

I think this is just bad UVs. You can click the ‘isolate’ box for each material on the right, and see which part of the mesh it corresponds to. I suspect the hand has 2 materials, and should have 1.