Bug in the new 4.19 Landscape LOD system? Update: UE-72934 still in 4.23 - occurs if camera FOV>90°

Development World Creation
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1

Since UE4.19 (at least) my landscape displays awful “popping” where, when moving towards a landscape, a part of the mesh briefly down-rezzes then soon reverts that resolution right back, correcting the mistaken down-res. The effect is that an area of the landscape in view suddenly deforms then pops right back to the way it was. This is constantly happening during movement - one area pops, then another area pops; the whole landscape writhes if you move fast enough.

Watching at high quality helps because the landscape jumping around can look like video compression artifacts. Watch how the crests of the dunes in the distance are dancing around:

The video compression makes it harder to follow the wireframe section at the end, but you can see that as you approach, chunks of mesh erroneously switch down a LOD then pop back. This is with the landscape LOD settings left at default.

If you stop moving towards the area mid-pop, it stays down-rezed, so it’s distance-based LOD at fault (well, screen-based). Likewise the problem stops if I force LOD off with console command “r.forcelod 0” or by cranking up the Landscape’s Details > LOD Distribution > LOD 0 = 5

Something has gone wrong because when you go BACKWARDS, the same thing happens - first it down-rezzes, then it pops back, and if LOD were working as intended, surely it would stay down-rezzed as you move further away, and likewise, when heading towards it surely it shouldn’t down-res as you get closer?

I’ve done some searching but haven’t found any reference to this behavior, is it a Thing? Am I missing something? Am I doing something stupid? Thanks!

UPDATE: This problem happens when the camera FOV exceeds 90. If I change the camera I can get it to stop. I believe it’s older than 4.19 and it still occurs as of 4.23 (the latest version at time of writing).

There’s a bug in the tracker now, and you can vote there to indicate the bug matters to you:

UE-72934

2

A little piece of video would greatly help, even if 1min long.

3

Have turned on LOD visualizers? Are you using level streaming?

4

Video added!

5

Which is the size of each tile in your map and how many tiles on it? Thats a composite world right?

I will try to reproduce this here.

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Yup, it’s a tile-based world. Tiles are 505x505 verts, (two verts per metre so 250m.) Currently there are 8 different landscape-meshes being duplicated via level-streaming into about 20 tiles active at a time (and another 20 either unloaded or “visible” set false)

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LOD visualization on shows that the popping can occur within a colored section of mesh without it changing color. Eg, the mesh section that pops and some of its surrounding mesh can remain the same color before, during, and after the down-rez. (All the landscape is streamed levels.)

8

I got a issue at home, a wall collapsed and I am a bit out of focus by now. I would report this as a bug and see what the dev team tells about this. I recommend for you to make a small project with the same terrain and submit along with the form with a link to the video too. I wish I could get a look into this right now, since Im quite at the point to deal with the open world environment for my game :confused:

The bug can be submitted here: Unreal Engine Community

9

I see similar issues with my landscape on 4.19 too. The odd thing is that it only happends when viewed on Oculus, but fine on Vive. It does these weird popping at certain angles. I also have trouble avoiding “moving artefacts” when approaching smaller landscapes (15x15 tiles). Im not using worldcomp, so this might be a different scenario than the OP. However, in general the landscape LOD’s seem really hard to tweak compared to 4.18.

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It would be great to hear from @J.Fisher if a bug report was sent and which is the tracking issue number, so we can vote on it.

12

Btw based on the release notes this is the behavior I would expect when using the new logic? Depending on camera position and angles different parts of the landscape will have higher percentages even at farther distance based on elevation changes. Not sure if it was intended?

13

I found a workaround: On my projects the bug only appears if the camera FOV exceeds 90 (all versions of UE).
That’s for regular projects ie monitor, but the workaround also works for Oculus Rift (at least for the project and version that I tested on Rift)

It’s now in Epics bug database. You can check progress and/or vote that the bug matters to you:

Further update: A quick check suggests I might not be seeing the bug in 4.23!
(I also notice that there is now a Camera option *Details>Camera Options>[extended]>Use Field Of View for LOD *which might be useful/related?)

14

As it was not clear for me:

I had the same problem with flickering Landscape lods in 4.22.3. I just switched to 4.23.1 and the described bug is fixed in 4.23.1
As already described it was only visible if the FOV is bigger than 90.