Editor gizmo and selection

Gizmo events

The base class FTypedElementViewportInteractionCustomization holds logic “to allow asset editors (such as the level editor) to override the base behavior of viewport interaction”.

For example, the derived class FActorElementLevelEditorViewportInteractionCustomization is used when you try to move around an actor in the level.

The main functions are GizmoManipulationStarted, GizmoManipulationDeltaUpdate and GizmoManipulationStopped.

• GizmoManipulationStarted
  • calls GEditor->BroadcastBeginObjectMovement (wrapper of OnBeginObjectTransformEvent)
• GizmoManipulationStopped
  • calls PostEditMove on the actor (with bFinished as true)
  • calls GEditor->BroadcastEndObjectMovement (wrapper of OnEndObjectTransformEvent)

Selection

USelection is the backend of the selection flow in the editor.

Notes:

• There is Actor::IsSelectedInEditor (same for components)
• There is USelection::SelectionChangedEvent and USelection::SelectObjectEvent
  • SelectObjectEvent isn’t called if we clear selection with the Escape key, so if you want to handle all possibilities for an actor use USelection::SelectObjectEvent with IsSelected().
• Use GEditor->GetSelectedObjects() (or other variants) to get a pointer to USelection (depending on the used functions some objects will be excluded from the list, for example use GetSelectedActors to get selected actors.)