Introduction to level of detail
Understand level of detail (LOD) and LOD indices, and learn about the LOD features available in Unity.
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Level of detail (LOD) is a technique that improves performance by reducing the rendering workload.
Without a LOD solution, Unity renders an object with the same complexity no matter the size of the object on the screen. For example, in one frame, a 3D model of a building might occupy the whole game view. Then a player moves away from the building and it might be only a few pixels high on the screen, but Unity has to render the same mesh.
With a LOD solution, as a GameObject becomes smaller on the screen, Unity can reduce the rendering workload using one or a combination of the following approaches:
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Reduce the number of polygons to render.
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Reduce the complexity or the number of materials to render.
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Reduce the number ofcomponents.Mesh Renderer
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Unity refers to objects representing levels of detail using indices, where a LOD with index 0 (LOD0) represents the most detailed LOD, and LODs with higher indices have progressively lower amounts of detail (LOD1, LOD2, and so on).
Left: at LOD0, meshes have a large number of small triangles. Right: at LOD1, the meshes have far fewer triangles, which are much larger in size.
LOD features in Unity
Unity implements two different LOD features:
Each feature has its advantages and uses a different format for LOD objects. The following table provides a comparison of key characteristics of the features.
Mesh LOD | LOD Group |
|---|---|
| The feature focuses on reducing the number of polygons to draw with minimum memory footprint and computational overhead. Does not optimize materials or number of draw calls. | A flexible solution with a larger memory footprint and computational overhead. When authoring LOD objects, you have the following optimization options for each LOD:
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| Provides the option to create LODs automatically on model import. | Requires manual authoring of each LOD mesh in an external tool. |
| Unity stores each LOD in the index buffer of the original mesh. | Each LOD is one or a set of Mesh Renderer components. Users can access and configure each LOD using the Editor interface. |
| Provides a smaller memory footprint compared with LOD Group. Has a smaller rendering workload overhead compared to LOD Group because Mesh LOD does not use any extra GameObjects, components, or meshes. | Has a larger memory footprint and computational overhead compared with Mesh LOD. |
| Provides parameters that control LOD transitions implicitly. | Lets users explicitly specify object size on screen at which a LOD transition occurs per LOD index. |
LOD transitions
By default, Unity displays one LOD at a time. When Unity transitions from one LOD to another, the transition is noticeable and abrupt.
To make LOD transitions smooth, enable LOD cross-fading. Unity renders both the current and the next LOD, and blends them together.
A sphere (LOD 1) blends smoothly into a cube (LOD 2) as the camera zooms out.
For more information, refer to:
Additional resources