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View-dependent LODs

A view-dependent LOD is a LOD that should not be visible from certain angles, thus making it a great target for optimization. In some cases there are areas in a level of where a player's sight is limited, such as densely populated areas, or areas near the edges of a world.

Figure 1: Visible side of a view-dependent LOD.
Figure 1: Visible side of a view-dependent LOD.
Figure 2: Non-visible side of a view-dependent LOD.
Figure 2: Non-visible side of a view-dependent LOD.

A common optimization technique for view-dependent Actors is to simply remove all back-facing and occluded geometry that cannot be seen from one or multiple points in space. These points, or rather sample points, can be generated from a camera position, a camera path or by setting up a Nav Mesh and generate points inside the volume using SimplygonNavMeshSampler.

Once inside Simplygon, these sample points will get handled as if they were omni-directional cameras. Geometry that is visible from one or more of these cameras will get weighted, a higher weight means higher importance. Simplygon's visibility pass will then decide if a triangle should be kept or culled.

This visibility pass can also aid material baking and UV generation. Simplygon can decide how much texture space is needed based on the level of visibility. Unused texture space from culled triangles will leave room for higher texture density for the ones that remain.

Visibility culling can be used with Stand-Ins.