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Wednesday, February 3, 2016

Improving building LOD

Most rendering engines need some form of level of detail management to deal with complexity. In traditional games there is a lot of hand work going into creating multiple views of the same content. A view of a distant tower in a game is likely crafted as an individual asset, it is not a byproduct of the high-detail version used for closeups. There are some very good commercial solutions to produce multiple LOD for assets, even then a lot of massaging is often required.

In our case we want full automation. Our creation tools should be used by people with no understanding of what LOD means. There is no single silver bullet in this case, it is more like a cocktail of copper bullets, but here is one:

If you think about it, distant LODs are necessarily viewed from afar. This is something we can exploit. Most buildings will have rather simple facades compared to their convoluted interiors. If we know the camera cannot be inside a given LOD version of the building, it is safe to remove whatever complexity is not contributing to the exterior. The result is you can cut a lot of information right away without having to lower the fidelity of the facade at all.

You can see the method in this video:

The method cuts from 80% to 90% of the information. It uses raycasting to determine the likelihood of a portion to be seen from outside. To make it quicker, it first discards portions that are trivially known to be outside. For instance all content that projects directly into the bounding box of the object we know is exposed, so there is no need to test for occlusion. Then it removes the portions we found are never exposed. This produces a rather noisy version of the interior. To this we apply some filters to clean it up and produce the lean shapes you see in the video.

The buildings in the video are voxel creations by Landmark players during EverQuest Next's workshop competitions. They are stunning and at the same time were created by someone who has no knowledge of Maya, 3ds max or traditional 3D modeling. For this very same reason we do not want them to think or worry about how their content looks at different LODs. It just has to work.

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