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Big gap in volumetric lightmap

Hi, I am experimenting with the new volumetric lightmap feature. I turned my samples up to 100 (default is 200, decreasing the number increases the resolution). I'm getting a big empty spot in the middle of my test room where there are no samples, so movable objects receive the skylight without any occlusion.

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By the way, I am using both a lightmass importance volume and a character detail lighting volume on this room.

Product Version: UE 4.18 Preview
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asked Sep 26 '17 at 03:38 PM in Rendering

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avatar image Wilkes Sep 29 '17 at 05:06 PM

I got the gap to go away by removing the long wall on the right side, leaving the room with 3 walls. This is obviously not ideal. Any idea why having an enclosed room is causing a void in the volumetric lightmap?

I also tried with and without the importance volume and character detail lighting volume. Changing the sample resolution didn't do anything either.

avatar image motorsep Sep 29 '17 at 06:57 PM

Any chance you can put up screenshots showing the issue ?

avatar image DanielW STAFF Sep 29 '17 at 07:16 PM

Yeah needs a screenshot demonstration.

Samples can be removed if the entire brick has nearly the same lighting values - that would happen inside a fully enclosed room with no light sources. That won't increase actual leaking - the parent had the same value. It can be confusing when looking at the samples though.

avatar image Wilkes Sep 30 '17 at 04:11 PM

I added two screenshots in the main post, are they not visible?

If the lighting value remained the same where there weren't samples, that would be fine, but the object in that area is instead lit as if it's outside being exposed directly to the skylight.

Here is a video I recorded: https://www.youtube.com/watch?v=z1D_uEWup68

avatar image DanielW STAFF Oct 02 '17 at 06:29 PM

The screenshots in the main post didn't come through for some reason.

Thanks for the video, that shows the bug very clearly. That's definitely not explained by trimming of bricks with nearly equal values. I will do some tests with stationary skylight here to see if I can figure out what's going on. If you have a small project which reproduces it to share that would help me a lot!

avatar image Wilkes Oct 04 '17 at 04:26 PM

Unfortunately it's part of a large "experiments" project. I might have time to recreate the scene in an empty project, but I'm fairly busy. Thanks for taking the time to look into it!

avatar image Wilkes Oct 13 '17 at 04:43 PM

Any news on this? Is there an issue tracker entry for it that I can follow?

avatar image Wilkes Sep 30 '17 at 04:52 PM

I just discovered that the problem goes away if I set the skylight to static and rebake!

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2 answers: sort voted first

Your samples probably overshoot the "Volumetric Lightmap Maximum Memory Mb" size, then the engine simply leaves out samples on arbitrary places (it guesses where they are unneeded the most) to push the memory consumption down under the threshold. Increase the number or increase the "Detail Cell Size" to thin out he samples and see if it helps.

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answered Oct 13 '17 at 05:46 PM

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I have the same problem. When upgrading from 4.17 to 4.18, samples are not placed where I need them, as if there is some "collision" in the way. What is more, static skylight produces no lightning on the floor (it used to light it ok in 4.17).

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answered Nov 02 '17 at 09:43 AM

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