Delaney King

Delaney King

08-11-2022

11:47

Another quick gamedev question: Level Of Detail models for trim sheet models? I did answer this one earlier but there is a lot to trawl through - I can't even find the link, so I will quickly do it again.

Okay so with trim sheet models, your texturing relies on the way you cut up your model. Often removing polygons will create seriously noticeable pops, and poly reduction tools can struggle to get a good result. The trick is to manually create a LOD that uses a baked map.

I am going to use polygon acadmy's brilliant trim sheet video as an example, so I can also plug this great video.

So this is the end result and you can see to make the floor asset of the kit, a lot of geo is needed. This is a very clean, well made model, and there are loops to prevent warping as the texture is bent.

If you start chopping out that geometry in your LOD, you can imagine things start to fall apart. So in order to make this LOD very well for an open world game, I would create a low poly version over the top of each of the modules in the kit (pillar, floor, roof)

I would then create a texture set that takes all the details of the trim sheet and maps them to low geometry. (To do this, I have to do some trickery, as the normal maps would be rotated by the trim sheets)

The manual LOD would essentially snapshot the floor here as a top down projection. That would then allow me to start pulling out all the geometry that is there to hold the trims in place.

In my first LOD, I would want to keep the floor as round as possible to avoid popping, and remove all the interior faces. This would reduce my quad overdraw as the object gets distant. The same goes with the pillars, which I would bake over to a simple cylinder in the first LOD

The baked over textures for the LOD won't have anywhere near the amount of detail as you get with the trim sheet, but remember this is for an object in the distance. Up close, you want all that delicious trim detail.

By moving from a trim model to a baked unwrap, you can really get crunching down on your triangle count, and you get the benefit of all those fine poly details becoming filtered pixels- which blur nicely and don't scintillate and flicker like geo does.

If you want to be extra speedy, you can take all your manually unwrapped low poly distance LOD models for a region and atlas them into one texture and material. This means entire distant villages can be batched down into a single draw call.

Now, this is a lot of work. Not gonna lie- manual LODs take some time to match up and make. But the benefits can be huuuuuuge, both visually and performance wise. Plus, you get so much detail up close from using trim sheets.

Now one last trick- you can fade (dissolve) a LOD model over the top of higher res model using a shader that takes distance into account. This can smooth the pop as the high poly switches out. High >> high with low over the top fading in >> low

As always, I hope that helps, and do stop by that video tute and hit like. It is absolutely spot on.



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