Actor Mobility

Setting that controls whether an Actor can move or change in some way during gameplay.

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The Mobility setting controls whether an Actor can move or change in some way during gameplay. This primarily applies to Static Mesh Actors and Light Actors. It is located in the Actor's Details panel, under the Actor's Transform coordinates.

Mobility setting in an Actor's Details panel

The Mobility setting in an Actor's Details panel.

An Actor that supports this setting can have one of three mobility states:

  • Static

  • Stationary

  • Movable

Static Actors

Static mobility is reserved for Actors that will not move or update in any way during gameplay.

  • Static Mesh Actors whose mobility is set to Static have their shadows contribute to pre-calculated lightmaps that use Lightmass to generate and process them. This mobility makes them ideal for structural or decorative meshes that never need to relocate during gameplay. Note, however, that their Materials can still be animated.

  • Light Actors whose mobility is set to Static contribute to pre-calculated lightmaps that use Lightmass. They illuminate the Level for Static and Stationary Actors. For Movable Actors, they use an indirect lighting method like Volumetric Lightmaps.

    For more information, refer to the 静态光源的移动性 page.

Stationary Actors

Stationary mobility is reserved for Actors that can change during gameplay but not move.

  • Static Mesh Actors whose mobility is set to Stationary can be changed but not moved. They do not contribute to pre-calculated lightmaps using Lightmass and are lit like Movable Actors when lit by a Static or Stationary Light. However, when lit by a Movable Light, they will use a Cached Shadow Map to reuse for the next frame when the light is not moving, which can improve performance for projects using dynamic lighting.

  • Light Actors whose mobility is set to Stationary can change in some way during gameplay, such as having their color or intensity changed (to be brighter or dimmer), or even being completely off. Stationary lights still contribute to pre-calculated lightmaps using Lightmass but can also cast dynamic shadows for moving objects.

    Too many Stationary Lights affecting the same Actor can have a significant impact on performance. Refer to the [])(building-virtual-worlds/lighting-and-shadows/light-types-and-mobility/StationaryLights) page for more information.

Movable Actors

Movable mobility is reserved for Actors that need to be added, removed, or moved during gameplay.

  • Static Mesh Actors whose mobility is set to Moveable cast a fully dynamic shadow that does not cast pre-calculated shadows into the lightmap. When lit by Lights with Static mobility, they will use an indirect lighting method like Indirect Lighting Samples to illuminate them. For Lights with Stationary or Movable mobility, they will only cast a dynamic shadow. This is the typical setting for any non-deforming mesh element that needs to added, removed, or moved in the scene.

  • Light Actors whose mobility is set to Moveable can only cast dynamic shadows. In addition to being able to move the light during gameplay, they can also change their color and intensity during gameplay. However, care must be taken when making these lights cast shadows since their shadowing method is the most performance intensive. It should be noted that non-shadowing Movable Lights are inexpensive to calculate due to Unreal Engine's Deferred rendering system.

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