Overlapping Generated Lightmap UVs

[MiriamAteo]

Hi all,

I’m getting a warning on some of my assets that the lightmap UV is overlapping - the problem is, I’m already letting the Unity importer generate them for me. Is this possibly a bug in the importer? Or are there situations where the importer simply isn’t able to generate proper lightmap UVs?

I also get weird coloured splotches on my lightmaps, so it isn’t just a spurious error message but really an issue with my UVs. See attached files for pictures of the error message and lightmap results.

Edit: I think I found the problem. Unticking “Optimize Mesh” and “Weld Vertices” in the import settings makes the UV warning disappear. Still seems like odd behaviour by the importer - this makes me think the UVs are generated before changing the mesh geometry for optimizations, which makes little sense to me.

Also, I am still getting random colourful patches in my lightmaps (bright red, green, teal). It looks like light bleeding and I tried upping the UV margin / lightmap padding. However, the margins are at 32 pixels, padding is at 12 texels and I’m still getting these patches. There is no coloured light anywhere in the scene, so I don’t even understand where it would pick up those patches. Basically, there is no part of the lightmap where it should legitimately be bright red, I don’t even have objects with red diffuse that could be scattering red light to nearby objects…

Edit2: Nope, getting the overlapping UVs warning again even though vertice welding is still disabled. At this point I’m pretty much at a loss, I have no idea what I changed. I was playing around with different Hard Angle settings for the UV generation, but setting it back to the original value doesn’t make the warning go away. Please help.

[MiriamAteo]

Anyone?

[RichardSim]

I see this too in the 2018.1 beta’s - was looking around for a fix and found this thread.

[UnityLighting]

1. you must generate lightmap UV for your model

2. You can increase Lightmap Scale to have higher resolution for certain models

Send some screenshots from “Baked Resolution” mode fro m scene view

[Glowing_Slab]

I’m also seeing this problem.

[soleron]

This may be an erroneous warning.

But in some cases, the unwrapping is incorrect. (Especially if you are using Automatic unwrapping with a complex model.) You may get problematic triangulation, or some areas have not properly expanded. But even when you have made sure that it is 100% properly unwrapped, there may be other reasons. i.e. the way unity constructs the lightmap.

Try either increasing your lightmap padding in unity, or the UV padding in the 3d software you use. IF your model is too complex, try breaking it down to pieces. i.e. avoid unwrapping an entire room with the furniture as a single lightmap atlas. There are many reasons this can happen. Try eliminating he most obvious by making sure your Lightmap UV page looks clean and simple. (Modular modeling helps a lot in that direction)

[AlexanderZotov]

I have the same problem with ProBuilder asset. Even creating a simple cube causes this warning.

[zortech]

Same issue in 2018.1.3f1

[P_Jong]

Same issue in 2018.2.0b10 with creating a new shape (cube) with ProBuilder.

[kristijonas_unity]

Hello! As others in the thread have already noted, Generate Lightmap UVs is not a sure fire way to remedy lightmap problems. For more complex meshes, the best practice would be to unwrap them manually in a 3D modeling package.

If you want, you could provide us with a link to your project/scene so that we could investigate in detail. Thank you!

[SamRock]

@kristijonas_unity

Hello! As others in the thread have already noted, Generate Lightmap UVs is not a sure fire way to remedy lightmap problems. For more complex meshes, the best practice would be to unwrap them manually in a 3D modeling package.

If you want, you could provide us with a link to your project/scene so that we could investigate in detail. Thank you!

I have having the same issue when using Progressive Lightmapper. I tried increasing or decreasing resolution, texel and generating UV map. Still same

[Switch2803]

I had the exact same issue - it was because I had a giant floor and wall mesh set to lightmap static, meaning the generated lightmap UVs for the important meshes were compressed to such a point that they overlapped.

After unticking lightmap static for these large meshes and then re-baking, the issue was gone. Hope it helps someone!

[rasmusn]

Hi MiriamAteo,

I would recommend you to read this page which was written exactly for situations like yours:

Unity - Manual: Fixing lightmap UV overlap

Unity’s UV generator is not perfect. For example low pack margin values can cause UV islands to be close together. This may or may not cause an actual UV overlap - this also depends on your lightmap resolution. Annoyingly many variables are involved here (which is why the root cause can be several things).

To solve the problem you must find out where and why there are overlap. Here’s a gif where I show how to inspect a cube:

Some weird unrelated warnings pop up in the gif, but that’s just because I am using a dev-version of Unity. The overlap warning did disappear, I promise
Also I should note that changing the lightmap resolution is often not the best way to solve this problem as it increases memory usage. Ideally you want to adjust UVs, for example by increasing pack margin. But in order to make a good decision you first have to understand/see the overlaps.

Your version of Unity maybe slightly different UI-wise, but you should be able to find the same panes/windows.

I cannot explain why “Optimize Mesh” and “Weld Vertices” have an impact on the warning. I would leave them at the defaults unless you have a good reason to change them. They should not be needed to avoid UV overlaps.

Regarding the unexpected coloring, this may be due to lightmap compression. Try turning it off and see if that helps (in Lighting window).

[Max_Bol]

Currently, I’m using Unity 2018.2.0f2 and I can guaranty that Unity, at least in that version, isn’t able to manage its lightmap system properly.

When I look at the OV Overlap, I’m seeing what’s supposedly overlapping… and that’s bogus at best.

First, the biggest issues comes from how Unity manage the Lightmaps UVs islands alignments within the Lighting engine system.

It does it on a per-mesh basic regardless of whatever Generate Lightmap UVs is active or not.
If ALL the assets on the same lightmap are similar in size, the issue won’t be seen much, but if the assets have quite the variation in sizes, then the UVs generated for the Lightmap will be screwed beyond saving regardless of the Lightmap Parameters set on the renderers in the scene.

First, let’s show an example of who bad the system manage the UVs, currently:

Let’s start with an example. I made this semi-modern medieval building by modeling (including a clean manually optimized UVs unwrapping) pieces that were assembled in Unity. The main reason why I did it as a modular assembly is because I can create multiple buildings with the exact same pieces.

Now, with a Lightmap Resolution of 16 Texels per Unit (which is at least 2x more than I would normally allow to such a simple asset that isn’t looked up as close )… Let’s see the overlapping.

If I the lightmap to use my own UVs (disabling the Generate Lightmap UVs option) :

Ok. It returns us a warning that 110 object have overlapping UV’s. We can see that some parts are overlapping in the Scene view. What if I use Generate Lightmap UVs then?

Sacre-bleu! Isn’t that worse?!? Now the warning tells me there are 143 objects with overlapping UVs.

Now, let’s see what the Lightmap UVs actually look like…

The best case was with the option Generate Lightmap UVs disabled so let’s start with it.

Mmm. The light map basically used quite a small bit of the available space. Not only that, but you can see that some stuff is really tiny in the space.

By the way, this test was done with Lightmap parameters set so that the big parts (walls and roof) are at “Medium Resolution” while the small parts (doors, frames, windows, etc.) are set at High Resolution. Fact is that I try with both at Medium and with the one I just mentioned and the size of the UVs on the Lightmap were identical in sizes.

Let’s take a closer look at the part, in the preview, that sounded like it was really overlapping in both cases : The windows.

Okay, the UVs are like what I manually applied in the 3D software, but mirrored in both X and Y.
(I added a screen shot of the UVs in the 3D software, the mirrored it in both X and Y to display the similarity.)
The parts that aren’t visible in Unity’s Overlay Lightmap UVs but are visible in the 3D software are parts of another window model that isn’t used in the scene right now.

But, we can see the problem there. The UVs island on the Lightmap are too close. If I was in controls of those specific features, the 2 solutions would be to regenerate the UVs in a way that doesn’t stick them as close as that or to allow the UVs island to take more space in the Lightmap so that there’s at least enough space (padding) between each island, right?

I tried many things by changing the Lightmap Parameters and allowing an higher resolution. Didn’t change anything unless I put a resolution that is far too high. Raising the Lightmap Size didn’t changed neither.

On thing I do find quite strange is how the lightmap resolution in the Scene Lightmapping Settings has some extreme change in the way it handle the lightmap uvs. The change between 2 and 8 were noticable for all the sizes. Between 8 and 32, the changes mostly only affected the big assets like the walls and roofs while the small assets seemed to keep it really small in comparison. (There’s maybe a 20% difference in size between 8 and 32 for the small asset while the big asset tripled in size.)

When made it pass 34, suddently, the UVs island of the lightmap extend onto the whole area (filling that big black square spot you can see in the screenshot above.

So, adding more available space in the UVs is, at most, impossible to predict unless I start raising the resolution through the roof just so that the original padding from the UVs can enough to avoid Unity to think something is overlapping.

I’ll post this now and will follow with another post as I can’t post more than 5 image per post.

[Max_Bol]

Now, what if I let Unity handle the UVs? Why was is even worse then? Shouldn’t it be able to put enough space (padding) between the parts? The answer is: No. The way the generated UVs are made… basically works as great as if you let any 3D software handle the UVs by itself.

Here what’s the generated UVs looks like :

Sure, it’s “cleaner” than the one I made since the one I made also included 1 window that isn’t used yet in the scene, but why did unity stick those UVs island so close? It’s basically generating Overlapping UVs by itself, right?

Now, I though “Well, it doesn’t have enough padding. That’s all.” So I raised the Lightmap Padding in the Scene’s Lighting’s settings. Well… that didn’t work because that padding setting actually only affect the space between the WHOLE object in the Lightmap and not the islands generated by the Generate Lightmap UVs option.

Well, since that Padding option in the Scene Lightmap option is useless for this problem, let’s look at the Generate Lightmap UVs advanced option…

Nothing much that looks like padding. Maybe that Pack Margin… If I raise it, what is it doing?
Well, it’s “kinda” like a padding option, but it comes with one really big problem which you can see here :

That’s if I set the Pack Margin at 64 (maximum).

As you can see, it did add padding between the UVs island, but… it did it so by reducing the size of the UVs.
Even so, Unity still see Overlapping UVs ieven in those case. Sure, the warning dropped at 72, but that makes the UVs a bit too compacted.

The issue clearly comes from how Unity Lightmap system sizes things up.

Also, I tried to force the small asset onto their own Lightmap, but didn’t worked because, in the end, the lightmap size and Lightmap Resolution’s texels per unit is what’s determining the resolution of each part in a generic way. You can’t have 1 part with an higher resolution than another part or, at least, it doesn’t allow me to do so regardless of the settings I apply.

[rob8861]

@Max_Bol this is 100% reproducible on my end, on pretty much every unity version. I honestly have no clue how anyone can fully eliminate 100% of the UV overlapping warnings on complex geometry (not cubes). To add to what the OP has already stated above, I was even able to reproduce this behavior using only Unity’s primitive geometry where you have no control over the UVs.
I am by no mean a computer lighting expert but this system is not very user friendly. 99% of the times, I see no issues such as bleeding etc, yet Unity still complains. In certain cases where the geometry is very simple, increasing resolution solves the overlapping issue. however, when the models are more complicated in nature , tweaking the settings will not ( or in my case never) clear 100% of the warnings.

This issue does not exist in Enlighten so why is it such an issue in Progressive?

[rasmusn]

@Max_Bol

Currently, I’m using Unity 2018.2.0f2 and I can guaranty that Unity, at least in that version, isn’t able to manage its lightmap system properly. […]

Thank you for that detailed analysis.

Let me first say that I understand your frustration. The current behavior is confusing and difficult to interpret. We are aware of it and are working to improve the situation. Let me try to address some of your comments.

The UV overlaps that Unity warn about refer to charts/islands that are too close together in the discrete lightmap, i.e. separate charts that sample from same texels. This means that you can pass in a UV layout without overlaps, and the warning may still fire if the final lightmap has charts that are too close. This may happen for example if lightmap size is too low. Our chosen wording “UV Overlaps” is misunderstood by many (with good reason) and we will probably rename it.

The reason you see more overlaps when using Unity’s built-in UV Generator is presumably that you set the Pack Margin setting relatively low compared to the lightmap size (256^2, 512^2, 1024^2, …). Increasing the Pack Margin should lower the amount of overlapping texels, but it will not necessarily eliminate it. Pack Margin controls the amount of space between “UV islands” in the UV layout. Another reason may be that you used a low Light Padding value in the Lighting settings window. This controls amount of space between object.

Even if your UV layout happens to be perfect (generated or hand-authored), it may not work for particular lightmap resolutions/sizes. Charts may end up sampling from same texels because resolution is too low even when there are no overlaps in UV space. All these interdepedencies makes it very hard for the user to address the overlap issues you are facing.

You may argue “Why doesn’t the UV Generator just calculate a proper spacing?” The primary problem is that the proper spacing depends on the chosen lightmap size and this information is scene-specific and therefore not available to the UV Generator (which is part of the mesh importer). Technically we could provide that information but this is not trivial since that would mean that the imported mesh asset depends on a particular scene and thus cannot be used in another scene. Also, it would mean that the mesh asset (and its UV layout) should change whenever you change the lightmap sizes. There are ways to solve this of course, but I am just trying to illustrate it is not a trivial matter.

I cannot guarantee anything specific but this is what we are talking about so far:

• In the short term: Improve wording and/or UI of “UV Overlap” to reduce likelihood of misunderstanding.
• In the long term: Implement alternative packing algorithm that will eliminate texel overlapping altogether.

Additionally, we already added a link to a docs page (mentioned below) next to the warning in the editor. I think this was part of 2018.3.

You presumably already did this, but if you may find this manual page that describes the problem interesting:
https://docs.unity3d.com/Manual/ProgressiveLightmapper-UVOverlap.html

[AcidArrow]

@rasmusn

“UV Overlap”

I don’t know how feasible/easy would be to implement this, and I fully admit that there could be implications and complexities that I’m unaware of, but could the UV overlap/bleeding warning give us a percentage of how much larger the padding should be to not be overlapping/bleeding?

I hand author my UVs and also mainly use unique meshes per scene (so I could potentially fine tune the padding to be almost perfect for the one scene and lightmap res they are used) and I usually know how much padding I already have, so a percentage would save me a lot of “let’s repack this with slightly larger padding and see if Unity stops complaining”. I mean, I can take a look at the resulting lightmap and make a fairly educated guess, but that still leaves a lot of trial and error, so a percentage would be nice.

Just an idea.

[rasmusn]

@AcidArrow

I don’t know how feasible/easy would be to implement this, and I fully admit that there could be implications and complexities that I’m unaware of, but could the UV overlap/bleeding warning give us a percentage of how much larger the padding should be to not be overlapping/bleeding?

I hand author my UVs and also mainly use unique meshes per scene (so I could potentially fine tune the padding to be almost perfect for the one scene and lightmap res they are used) and I usually know how much padding I already have, so a percentage would save me a lot of “let’s repack this with slightly larger padding and see if Unity stops complaining”. I mean, I can take a look at the resulting lightmap and make a fairly educated guess, but that still leaves a lot of trial and error, so a percentage would be nice.

Just an idea.

Hmm, interesting idea. Thanks. Calculating such a percentage seems a bit daunting. It depends on a bunch of different settings and scene contents. I am not sure but I think that it would be more difficult to calculate such a percentage than it would be to simply make layout that is guaranteed not to overlap to begin with (which is already on our todo list). So I think it would be more wise to spend our time on that instead.

[RickshawDerpyDerp]

I made all my own UV’s specifically to avoid this problem and Unity generated new lightmap UV’s for an object anyway, even though I marked it not to. I am using a simplified mesh with no UV’s as a mesh collider and wonder if it generated UV’s for that and is basing the Lightmap UV’s off of the collision mesh?