When to LOD when to not LOD?

jordank95

whats the general rule for setting up LODs? What should be LODd? Am I setting up LODs for every mesh in my game? Or only the ones that are higher polycount? Can UE4 do auto LODs easily or should I be doing them all by hand? Seems really time consuming if I need to do LODs by hand for all of my meshes in my game. 

Mirbobo

If your asset is already low poly there's necessarily no need to create LODs, sub 1k vertices for example, or a small props that get culled away early anyway. These days creating LODs can be pretty much completely automated and the UE auto-LOD generally does a good job creating LODs for your props. For more specific cases you might need to create LODs by hand, but that shouldn't really be a major time sink. There's also Simplygon, that for example also let's you create HLODs for your objects and so on.

For the rule of thumb you want to have a noticeable drop between you LOD levels, so reduce anywhere between 30-50% of vertices from your model each level.

jordank95

Mirbobo said:

If your asset is already low poly there's necessarily no need to create LODs, sub 1k vertices for example, or a small props that get culled away early anyway. These days creating LODs can be pretty much completely automated and the UE auto-LOD generally does a good job creating LODs for your props. For more specific cases you might need to create LODs by hand, but that shouldn't really be a major time sink. There's also Simplygon, that for example also let's you create HLODs for your objects and so on.

For the rule of thumb you want to have a noticeable drop between you LOD levels, so reduce anywhere between 30-50% of vertices from your model each level.

Got it. Thanks. As for Auto LODs, is this something I need to enable in UE or is it already doing it automatically?

FourtyNights

This should get you started with UE4's automatic LODs: https://www.youtube.com/watch?v=5KeGMmUFeL4

poopipe

Assuming you're not given onscreen tri-counts to hit then you should aim to LOD when triangles get smaller than a pixel  - it's at this point that things become extremely inefficient. 

Because I'm old and I've worked mostly on very detailed console FPS games I become uncomfortable when people chuck just stuff through simplygon  and assume it'll all be fine. 

Below is an example of the sort of thing Simplygon etc. can't do well.  The software simply isn't able to pick out the important  structures and break them down into primitives in the same way that your brain can.
If you run something like that through Simplygon you'll get decent results for the first couple of levels - it'll remove segments in the right places etc  - but once you want to drop the tricount to  3-4% of the top LOD (as in the image below) things tend to get pretty messy. 

For situations like this a couple of manual LODs right at the bottom can save a significant amount of on screen geometry if the assets are widely re-used and take very little time to make 



* I know the remesher mode will make a pretty good effort at achieving the above but nobody wants to UV that crap by hand and you're paying for an extra texture set if you accept the Auto UVs