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Landscape grass type LODs All showing at once in map.

I'm working with landscape grass types, and after putting an LOD on my grass I realized upon closer inspection in game that both of the LOD's are visible at the same time even though their distance settings are appropriate. It renders fine in the static mesh view window too. Is there a known fix for this? I'd love to be able to work with an optimized grass system while still using the Landscape Grass Types.

I've attached two images below as example:

What it should look like for face count: alt text

What it looks like in engine: alt text

Product Version: UE 4.8
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asked Jul 07 '15 at 06:46 AM in Rendering

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avatar image RyanB STAFF Jul 07 '15 at 04:19 PM

Are you positive that it is multiple LODs doing that? How is that mesh placed?

Is it one static mesh placed by hand or just an instance from the grass system that you zoomed in on?

avatar image JoshieZombie Jul 07 '15 at 09:57 PM

Howdy there! I'm positive it's multiple LOD's. I've made a video below where LOD0 is my standard grass_mat, and LOD1 is a bright red debug_mat. I've shown in the video a comparison between the static mesh and the instanced 'Landscape Grass Type' LOD's. Hopefully the video will be helpful in discovering the source of the problem.


avatar image RyanB STAFF Jul 07 '15 at 10:00 PM

If you place a single instance by hand does it do that?

And also is that the only grass mesh over there?

Its hard to see whats going on in the video since the isolated pieces don't always show it, sometimes you see the red material by itself.

avatar image JoshieZombie Jul 07 '15 at 11:29 PM

Oh wow, that was quite prompt! :)

I just got back from lunch and made another video to show some more isolated examples as well as a mass example and how it seems to pop LOD's on the grass map grid:

I also tested it just now with the foliage tool while the video was uploading. The LOD's still appear at the same time as each other with the normal foliage tool. The only difference was that no matter how close I got to even one instance in the foliage tool the LOD1 never went away.


avatar image JoshieZombie Jul 09 '15 at 12:03 AM

In case a video perhaps is not the best way to explain due to time constraints or other reasons I'll add some explanation from the video below:

I've now tested with a single static mesh vs a single landscape grass type. I also tested with two landscape grass types near each other, as well as an entire field near the end of the video for a mass scale example. The static mesh performed as expected the entire time so I'll mostly be speaking about the landscape grass type. Testing these things brought a couple oddities to my attention so I wanted to focus on them and explain my results clearly.

•Single landscape grass type test:

It performed much more as expected, but still had some quirks. There seems to be an overlapping range on the LOD's. When I am up close, LOD1 is not rendered and LOD0 is rendered as expected. If I back away from the instance ~10' LOD1 will render while LOD0 is still rendered. LOD0 and LOD1 render simultaneously for another ~10' until LOD0 finally pops out if I continue backing away. This overlapping range is apparent in all examples below as well.

•Double landscape grass type test:

For this example I had placed two of the instances near each other ~10' apart to see how the LOD's would react. While I am up close and inside one of the instanced meshes LOD0 and LOD1 are both rendered. It seems as if the two of them act as one instance when deciding which LOD to render, and in this case they render both at the same time when up close. In order for LOD1 to stop rendering I was required to stand at an even distance between the two instances. I didn't really understand what may have been happening until I tried showing the massive scale example.

I have to split my reply because it is too long xD

avatar image JoshieZombie Jul 09 '15 at 12:03 AM

•Mass landscape grass type test:

I went ahead and painted a large portion of my hills with the grass and I turned up my culling distance on the landscape grass type. In this example I experienced both the LOD overlap distances as well as similar results to the dual test where multiple instances acted as one when deciding which LOD's to render. While walking through the field I found that it is doing this calculation on a grid system. So long as I am roughly in the center of one of the grid tiles LOD1 will not render and LOD0 will be prevalent within that grid tile. However if I am not quite in the center of one of the grid tiles LOD0 and LOD1 will both continue rendering at the same time.


I wanted to report this problem in detail, because it seems odd to me that there is an overlap distance on the LOD's. Doubling (nearly) the amount of geo rendering doesn't seem optimal. I also don't mind the grid system so much, I just find it weird that it recognizes and performs LOD switches as groups of instances; and that I have to be near the center of this group for it to pop LOD1 out. If any more clarification is requested I'll happily oblige and provide feedback as requested :)

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2 answers: sort voted first

Oh my god I'm such a dork.

My sincere apologies. Aside from the weird behavior I experienced, it seems I just needed to turn up my LOD distance on LOD1. I'll just crawl back into my cave of work now.


Thanks Ryan for working with me again even though it was a problem of my own settings. :)

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answered Jul 09 '15 at 12:42 AM

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I'm having the same problem. How did you solve this?

I've been messing around with grass but I can't find anything call LOD distance that you are referring to. The closest thing there is probably LOD screen size which doesn't help much. I'm still getting all multiple LODs displaying at once.

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answered Sep 22 '15 at 02:10 AM

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avatar image JoshieZombie Sep 22 '15 at 02:52 AM

Lod screen size is correct. The lod's aren't technically triggered by distance, but instead by screen size. I don't remember what my exact values were but try setting your LOD screen size to something tiny like .0001 on your LOD1 and leaving LOD0 default. There will be LOD overlap still, but it pushes it farther out. If you need more clarification let me know and I can whip up an example tomorrow as I've already powered off my work-pc for the night. :)

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