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Distance Field AO is completely black underground


Our game is an open world title. We have many caves that go beneath our landscapes surface. Distance field AO looks fantastic as long as we stay above ground. If we go into our cave though, the AO goes completely pitch black and looks really ugly. We are counting on 4.9 and the much increased performance that DFAO will have, but it worries me that it will be completely pointless if we can't use it because of this bug.

Product Version: UE 4.8
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asked Jun 24 '15 at 11:04 PM in Bug Reports

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avatar image riuthamus Mar 26 '18 at 04:34 PM

This is still a confirmed bug in 4.19, I guess not enough games make caves? .... like.... for real?

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2 answers: sort voted first

Hi Josh,

I've reported this with UE-17667. This may be a limitation of the system rather than a bug, but still good to report either way. I'll update when I have more information.

Thank you!


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answered Jun 25 '15 at 02:09 PM

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Tim Hobson ♦♦ STAFF
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avatar image joshezzell Feb 18 '16 at 10:13 PM

I reposted about this issue (forgot I made this post).

Again, I am encountering the issue.

"I have had this issue before, but only when meshes were under a landscape piece. You can see what is happening here: http://grab.by/OeXG

Is this a known limitation of DFAO? If it is, it makes the feature practically useless for open world projects with caves and other features that intersect with landscapes.

EDIT: I should note that if I delete the landscape the cave entrance is sitting on, the DFAO goes back to normal."

avatar image Tim Hobson ♦♦ STAFF Feb 18 '16 at 10:30 PM

The bug is still backlogged at the moment, but there is a workaround that comes at the cost of later optimizations that have come in for DFAO and Distance Fields in general.

This particular issue is caused by the Global Distance Field that is used to combine distance fields to make them more efficient. You can revert to the older method by using the CVar r.AOGlobalDistanceField 0

avatar image joshezzell Feb 18 '16 at 10:35 PM

Ok, so there are plans to fix this in the future then. Is there an idea of when this would be done?

avatar image Tim Hobson ♦♦ STAFF Feb 19 '16 at 03:52 PM

It's backlogged which means it's just indefinitely on hold until it's added to the "To Do" list in planning phases or there is an immediate need for it internally.

This will likely be fixed in the future, but with the current task priorities It's not at the top of the list.

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PR with a potential fix: https://github.com/EpicGames/UnrealEngine/pull/4603

Before/After the change: https://imgsli.com/MTI5OQ

Shader edit only. Does not require source build.

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answered Mar 26 '18 at 10:47 PM

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avatar image tsnodgrass Mar 27 '18 at 12:46 AM

link on github doesn't seem to work, what are the steps needed to implement this?

avatar image Deathrey Mar 27 '18 at 06:18 PM

Gotta have a linked account.

avatar image Haoris Jun 07 '18 at 02:46 AM

This has no effect (4.19.2)

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