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LOD models are widely used in PC and console games, to optimize performance by reducing the vertex count and texture size for distant objects. However, I'm having a harder time finding out if they are typically used to increase performance in mobile games.

I've seen a few people in forums suggest that the CPU overhead for LOD models might actually outweigh the GPU gains on mobile devices. Another consideration is the more limited storage space on mobile, and LOD models/textures necessarily increase the total size of a game. Other than that, I can't find much information on the subject. The Unity documentation on LOD models doesn't mention mobile, and the Unity documentation on optimizing for mobile doesn't mention LOD models.

I know the first answer to any performance question is usually "profile it and find out for yourself"; however, in this case, I am helping to optimize a game that doesn't currently have LOD models, so profiling it would first require commissioning the artists to create enough LOD models that we can realistically profile the performance change.

Does the usage of LOD models typically provide noteworthy performance gains in 3D mobile games, or does the overhead for LOD cancel out any gains?

The specific title in question is a racing game.

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  • \$\begingroup\$ In order to profile this you wouldn't need good-looking LOD models. Just some model with less vertices than the original. Most 3d modeling programs offer some features to simplify a mesh automatically. The results might not be production-ready, but if you just want to test the framerate difference they don't need to be pretty. \$\endgroup\$ – Philipp Jul 30 '18 at 22:34
  • \$\begingroup\$ @Philipp Yes, but if there are 50 models in the scene, it can still take a while to generate the simplified meshes and plug them in as LOD variants. I'm hoping there is some generally applicable wisdom about this subject, but there may not be. \$\endgroup\$ – user45623 Jul 30 '18 at 22:47
  • \$\begingroup\$ You do not need to request enough LOD models from the artists, you can create a test enviroment with one model (and its LOD variants) that on the best quality has about the average polygons your models have, and have it repeated enough times, and you can get one such model pretty cheap on the asset store, even free if you don't care what the model is of. Generally applicable wisdom? LOD is good. Profile is good. The real question is how many variations to use. Too many: Too much CPU usage. Too few and the performance gains in GPU are not worth it. Test. It varies for hardware and game. \$\endgroup\$ – Theraot Jul 31 '18 at 1:01
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One of the things that makes it hard to answer this question is the quickly evolving diverse landscape of mobile devices. Not only are they getting more powerful and higher resolution, there are still lower-end phones and tablets that proliferate the market. If your target is only the high powered devices which have large screen sizes, then it makes sense. If you want to target a wide audience, then low-end devices may just need to use lower LOD models, without the runtime overhead of switching based on distance from the camera.

In short, LOD’s make sense for newer devices with higher power CPUs, which are slowly going to become the majority. However, note that whatever the resolution of a phone may be, it still has to fit in somebody’s pocket, so getting crazy with the level of detail in a model is not necessarily worth the overhead in that case. That may be left just to tablets. The best option is of course to check visually whether using lower LOD’s overall is visually acceptable on smaller physical screen sizes.

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