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Black lines appear on meshes at the corners of the lightmap

alt text

UE4 is rendering black lines in several places. I noticed that the lines are in the corners of the lightmap. I was able to fix some of it by changing the geometry a bit. But most of the time the line just go to another place of the static mesh. Far away the line appears as big black dots flickering. It's even worst in Oculus Rift, since the resolution is limited.

I'm using UE4.1.1 (It still visible in UE4.2, but my project don't work very well in 4.2) Radeon HD 4990

Product Version: Not Selected
blackline.jpg (189.3 kB)
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asked Jun 16 '14 at 03:43 PM in Bug Reports

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avatar image Jacky Jun 16 '14 at 03:50 PM

Have you set the lightmap UV's properly?

avatar image fabianoberlim Jun 16 '14 at 05:04 PM

Here's a overlay image showing where the problem is. The lightmap is plain simple. alt text

avatar image fabianoberlim Jun 16 '14 at 05:08 PM

As you can see, the lightmap is very soft. Far away it flickers a lot. alt text

bug.gif (139.1 kB)
avatar image Lovecraft_K ♦♦ STAFF Jun 16 '14 at 07:19 PM

Hi fabianoberlim -

In your final image the flickering black line appears to be on the wall with the door on it? Is this piece all one mesh? Can you post a screenshot of the wire frame for that particular piece that has the line and the UVs for the same piece (both UV sets if possible, please)?

I have seen an issue like this before, but it may be different for you. Please check to make sure you do not have stray vertices that are being imported with your mesh, either that are in this mesh or happen to be imported from another mesh with this particular one.

Let us know so we can begin to work on this error for you -

Eric Ketchum

avatar image fabianoberlim Jun 16 '14 at 09:27 PM

Hi Erick

Just for sanity check, here's a simpler mesh that happens to also have the problem.

It could do a better use from lightmap space.

Here's the mesh, a very very simple mesh.

I can't see what could be doing it. There's no stray vertices. Some of those problematic static mesh have n-gons and others are triangulated. Thanks for the help.

avatar image Lovecraft_K ♦♦ STAFF Jun 17 '14 at 01:36 PM

Hey fabianoberlim -

I have been looking at your asset, thank you by the way. I am not seeing any black dots or "marching ant lines" in my test project. I want to check what type of lighting do you have in the map. Also are you seeing these black dots on anything else, playing games or in a web browser? Are you using two monitors with your video card or are you using a crossfire setup with two Radeon cards?

Also I want to specifically check if you are using an Nvidia Graphics Card what is the driver version that you have installed.

Let me know -

Eric Ketchum

avatar image fabianoberlim Jun 18 '14 at 08:32 PM

Hi Eric,

Thank you for the help! I have just one black line left. I was able to fix it by changing topology and uv lightmap.

As you mention the light setup, I noticed that all the problems occurs under multiple static spot light. It didn't happen at all under the sun (directional light).

The dots and lines only appear when editor is in real time mode or inside the game. I don't have any problem playing games, even in the web browser.

I do have multiple monitors, but I not using crossfire setup. Every monitor is plugged directly to the card . Two monitors, and 3 when Oculus is on.

I don't have any Nvidia Graphic Cards available. Only Radeon HD 7990.

The last one and light setup.

Thank you!

blackline.jpg (166.7 kB)
avatar image Lovecraft_K ♦♦ STAFF Jun 18 '14 at 09:14 PM

Hi fabianoberlim -

I have seen this issue once before in relation to a driver issue with an Nvidia card, hence my question, and blending materials. It doesn't look like you are blending materials on your floor here, but it could be the bending lightmaps. Could you take a look at your Lighting Only, Lighting Complexity, and Detail Lighting and see if in those visualizations if you are getting anything reading as an error or unusual in the area where the line occurs.

Thank You

Eric Ketchum

avatar image fabianoberlim Jun 23 '14 at 06:26 PM

Hi Eric, Here's an image showing the problem. Light Complexity is all black. The problem also show up in the unlit image, but as soon I remove the baked light from object, moving the object or changing the lightmap quality, the problem disappear. The problem is also visible in Reflections. In the Buffer Visualization the bug is only visible in Final Image. Is there any file I can send you? Is there any way to export or open the baked light?

lightinfo.jpg (471.7 kB)
avatar image fabianoberlim Jun 23 '14 at 06:26 PM

Lit Pass

lit.jpg (155.1 kB)
avatar image Lovecraft_K ♦♦ STAFF Jun 23 '14 at 07:11 PM

Hi fabianoberlim -

You can view your baked lightmaps in the World Settings under Light Maps, but they are not ordered in any specific way.If you can upload to a Dropbox. the .uassets and .umap I will look at it and see if I can get the same error.

Thank You

Eric Ketchum

avatar image DarKris3 Jul 16 '14 at 02:01 AM

Hi Guys, I'm getting this same issue in my scene as well. Unfortunately the black marching ants are showing in my final render videos too since they only show when Realtime is turned on. So far as I can tell the assets that the black dots show up on are all using blended materials with roughness masks. Were you guys able to find a solution?

I had some overlapping spotlights on the floor like you guys mentioned in the earlier part of your thread. Once I moved the light cones away from each other, and baked lighting, the floor looked fine. But once I started deleting or moving other lights in my level to try and fix those areas, the black dots showed back up in the first area that I worked on.

fabianoberlim—You mentioned you were able to fix some of this by adjusting topology and lightmap? How did you do this? I have assets that look clean like your earlier ones and the black dots are showing up randomly where there are no seams in the lightmaps. Did you just add more subdivisions?

I’m using Unreal 4.2.1, and my videocard is: AMD Radeon HD 7700 Series I also tried opening my scene on my laptop that has a videocard of AMD Radeon HD 6700M series videocard and the black bugs are still present on there.

Any other advice that you guys have would be greatly appreciated. Thanks!

avatar image Lovecraft_K ♦♦ STAFF Jul 16 '14 at 05:59 PM

Hi DarKris3 -

I am not certain we were able to come up with a successful reproduction of this issue. What particular types of overlapping spotlights are you using? (Static, Stationary or Movable?)

Also Screenshots of the issue always helpful.

Thank You

Eric Ketchum

avatar image DarKris3 Jul 17 '14 at 06:55 PM

Hi Eric, Thank you so much for the reply!

I've attached some screenshots with the problem areas shown and left Sprite mode on so you can see where my lights are. I have several in the scene but all of the point and spotlights are set to Stationary. Some have Cast Shadows on and others do not.

After light baking, I tried turning off Realtime, and going to Unlit, Detail Lighting, Lighting Only, Reflections modes. There are tiny black seams present in all of these modes, but when I look at the individual assets in my Content Browser preview there is no problem.

Please let me know if you need more info? Thanks a lot! alt text

alt text

avatar image Lovecraft_K ♦♦ STAFF Jul 17 '14 at 08:58 PM

Hey DarKris3 -

This is a hard bug to reproduce. Can you try to set the lights which do not cast shadows to Static and then try to rebuild the levels to see if you still get the marching ants? Also and as a separate test, try removing one of the sphere capture actors from the scene and re-build.

Also what is your Radeon Driver version?

Thank You

Eric Ketchum

avatar image fabianoberlim Jul 18 '14 at 04:15 PM

DarKris3, I still have some lines. I was able to fix some of then, that the mesh wasn't so clean. The clean ones is bit more complicated, since I don't want to subdivide it. You can try move uvs around and send triangulated mesh or not to Unreal. It sometimes fix it or the problem just go somewhere else. My light setup looks like yours.

avatar image Lovecraft_K ♦♦ STAFF Jul 21 '14 at 04:13 PM

Hey DarkKris3 and fabianoberlim -

I have been working to recreate this error because I see your screenshots and I know that you are having a very annoying bug, but I've had no luck as of yet. I would say that it is a Video Card related issue, but both of you have different video cards and different drivers.

At this point I have to ask if either of you are willing to share an entire level including assets which demonstrate this error so I can start doing testing with a level we know generates the issue.

If you can please let me know I would need the Config, content subfolders and the *.uproject file. Depending on the size and how private you want the level to be please feel free to PM in the forums.

Thank You

Eric Ketchum

avatar image fabianoberlim Jul 21 '14 at 06:33 PM

Hi Eric,

I can share. The only problem is that my Content folder is huge. 6 Gb. Maybe I can share via DropBox, it will take a long time, but I can let the computer on for several days if needed. Do you have a better idea? I also tried to reproduce the bug, no success. Send me an email to fabianoberlim@gmail.com, so I can share the folder. Thank You

avatar image Lovecraft_K ♦♦ STAFF Jul 22 '14 at 02:14 PM

Hey DarKris3 -

In the areas that are creating the black marching ant lines, do the materials do any mixing of Normal maps or Roughness textures through math or LERP?

Thank You

Eric Ketchum

avatar image DarKris3 Jul 30 '14 at 09:31 PM

Hi Eric and fabianoberlim, Thanks so much for the responses! I apologize I have been on vacation for the past week or so and have not been able to answer.

Eric--I would be willing to share my file with you. It's about 2 gb. I can put it on Dropbox and share it with an email address of yours if you have one? I would like for it to stay private but at the same time getting to the bottom of this bug is very important as I can't make final render videos without the black dots everywhere.

The materials in question are not using a LERP, but as for Math I think they might be. The materials were very similar to the ones that were set up in the U4 Quixel Sci-Fi Hallway example. I used a parent shader that allows up to 6 masks and there are Math nodes (such as Subtract, Power, Add, and more) that were added into the mix. I only have one normal map assigned in each shader so it should not be trying to blend 2 of those together. However it would be trying to blend the normal texture along with the Roughness Blend Mask texture, and a Specular Roughness texture.

My Radeon Driver version is:

I'm going to run the light test that you suggested earlier on July 17th. Let me know if you need more info? Thanks again for your time everyone!


avatar image DarKris3 Jul 30 '14 at 09:49 PM

Hi Eric,

I conducted the tests you suggested previously, and unfortunately results were the same with the marching black ants still present when Realtime is turned on afterwards. I've been trying Medium, Preview, and Production qualities for lighting:

Test 1: I selected all my lights and turned off Cast Shadows, rebuilt lighting.

Test 2: I deleted both sphere capture actors in my main hallway, still kept all lights with Cast Shadows turned OFF. Rebuilt lighting.

Test 3: Deleted sphere capture actors but kept original light settings (some with Cast Shadows on, some with off), rebaked lighting.



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Hey fabianoberlim and DarKris3 -

So after much experimentation and discussions here, we have narrowed down the issue to one related to a video card driver. We are in the process of setting up a test with a Radeon card and drivers. I will let you know as soon as I have the results.

I was finally able to reproduce the marching black ant lines on an Nvidia card with the Beta driver installed but switching down to the WHQL release driver clears the issue.

Thank you both for your help and I will keep you informed.

Eric Ketchum

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answered Jul 31 '14 at 01:22 PM

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Lovecraft_K ♦♦ STAFF
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avatar image DarKris3 Jul 31 '14 at 06:56 PM

Great! Thanks a lot for the head's up Eric!!

avatar image fabianoberlim Jul 31 '14 at 07:38 PM

Thank you Eric!

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