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modular light bleed

So like everyone else i cant find any info on stopping the light bleed when using modular meshes. One person suggested using LPV as opposed to lightmass, is there no easy solution to this?

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asked Nov 19 '14 at 09:58 PM in Using UE4

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2 answers: sort voted first

I've spent a little bit and setup a demo with some different settings for LM resolution along with three different variations.

Demo Scene: https://www.dropbox.com/s/5dftr7q8rgh7nvv/ModularSeams_Demo.zip?dl=0

1 - UV islands setup on a grid in the UV 0,1 space for lightmaps. (Choose a target resoluton, I'll touch on this below before setting up grid) 2 - UV islands that are not on the grid 3 - UV islands rotated differently and not aligned properly

The scene consists of a row of tunnels (Similar to yours from what I could tell, at least enough to make a point) that is white washed to visibly see the seams. Then directly behind is a tunnel with two variations of materials (Rock and Metal Surface).

I did this setup for variations 1 and 2 with LM resolutions of 64 and 256 to see the difference. I only did one row with variation 3 @ LM resolution 64.

In the World Settings I adjusted the Indirect Lighting Quality to 2 and the Indirect Lighting Smoothness to 0.6. If you set this back to defaults you can see the smoothing between the seams is more harsh.

To go back to setting up UVs on the grid.

First you need to find the target resolution you want your lightmaps to be. I usually target 64 and snap the grid in my modeling software that way because if I need to up the resolution since I've set it up on 64 as a power of two I can increase it (ie. 128, 256, etc) and it will always be on the grid.

As an example, if I need to find the grid spacing for 64 I would do the following: 1 / (62-2) = 0.161290323 Source: http://www.reddit.com/r/UE4Devs/comments/246whl/the_most_important_thing_about_lightmaps/

Here is another thread that I was involved with going over some tips and things with LMs: https://answers.unrealengine.com/questions/92819/lightmap-uv-alignment.html

Here is my grid alignment/snapping for my UV. I've marked the hard edges as an idication for the four outside point. These need to be on a grid line. These are the hard edges of my mesh. The ones in the middle do not. The reason for this is since we're targeting a lightmap resolution of 64 we want these hard edges to be on a grid line because this will give us a hard shadow there. If the space were to fall between the edges of two grid points it would be considered shadowed and not hard. You can see this as edivident in the flatmapped UVs in the demo scene.

alt text

**World of Level Design is always a good resource for Lightmapping information as well. While it is using UDK/UE3 for their setups they are still used accordingly in UE4.**

I know this is a lot of information, but for the most part take a look at the demo scene (built with 4.5) and see if this helps any. I've included the three FBXs that are in the scene as well.

Can you post a screen shot of your LM UV or if your still having problems the asset (FBX) in question (if you dont want to post publicy you can send via the forums in a private message) and I can take a look to help out.

Let me know! :)


uv grid.png (101.5 kB)
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answered Nov 20 '14 at 10:29 PM

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Tim Hobson ♦♦ STAFF
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avatar image Reactant Nov 23 '14 at 05:53 PM

I'll have to give that a go when I get myself a new mouse, does Maya have snap to grid with uvs? I unfortunately use blender and don't think it has that ability, could I manually align just as well?

avatar image Tim Hobson ♦♦ STAFF Nov 24 '14 at 04:21 PM

I'm not sure if Blender has the ability to set the grid size or snap, but I did google both "Blender UV Grid Size" and "Blender UV Grid Snap" with results that look promising(?).

Manually aligning could possibly help but it the issue here would be that anything snapped to the grid line would be considered a hard edge and not shadowed. Anything falling on either side would get shadowed information baked. It may get your decent results but I've honestly not tried it so I couldn't say for sure one way or the other. Give it a shot and let me know how it works out. If that doesn't work we can keep looking and see how I can help you resolve your issue. :)


avatar image Reactant Dec 02 '14 at 04:00 AM

okay so i looked into blenders pixel snap mode, and still no luck, my uvs were 1024x1024 so maybe i need to change that, for now ive just been working at making large meshes in one piece, or rather multiple pieces and ticking combine meshes on import, still not the best solution but it suits my needs

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Hi Reactant,

It's possible to stop light bleed. I will, however, need more information on your setup though.

  • Are you using a fully static light or a stationary light?

  • Can you provide an image of the light bleed in question?

  • Have you setup your lightmaps with hard edges on a grid line in the UV and what is your lightmap resolution?

  • Have you built lighting on production? Light bleed can happen on lower levels since it's not production.

  • Are you using a lightmass importance volume?

This should be enough to get me started in helping you understand how to resolve the bleed.

Thank you!


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answered Nov 19 '14 at 11:06 PM

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Tim Hobson ♦♦ STAFF
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avatar image Reactant Nov 19 '14 at 11:26 PM

i tried a moveable light, stationary, and static. I dont think i properly set my lightmaps, im not sure the exact way of doing this in blender although i do have 2 uv channels. I usually test my scenes with production lighting so thats not it, and i just left the default lightmass importance from first person template.The first place to start would probably be my lightmaps. Thanks for the quick response too Tim.

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light bleed.png (1.2 MB)
avatar image Tim Hobson ♦♦ STAFF Nov 20 '14 at 04:36 PM

Before digging into the Lightmaps can you try one more thing. This looks like the seams that are caused by lightmass bake with modular assets that are planar to each other.

Go into world settings > Lightmass > and adjust the following:

Indirect lighting quality: 2 Indirect lighting Smoothness: .6

This will smooth the seams that are caused between planar modular meshes. If this doesn't help there are some things we can try with the lightmaps UV to get better results.

avatar image Reactant Nov 20 '14 at 04:53 PM

So unfortunately that didnt help much if at all. Do you think it could have anything to do with my mesh being too thick, or perhaps since it isnt just a flat wall and is actually a tunnel like object im getting problems

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