Description

Even after manually Deactivating a Niagara component, this Niagara component may be revived under certain conditions. This issue occurs when the following conditions are met before the Deactivated Niagara instance is in the Complete state

  • Calling APlayerController::SetViewTarget, etc., eventually calling APlayerCameraManager::AssignViewTarget() (the callback from this function causes the scalability manager to re-register the particle (callbacks from this function will cause the particles to be re-registered with the scalability manager).
  • The Niagara component is then Deactivated by the scalability condition (this means manual Deactivation is overridden.)

After this, the Niagara system is respawned when the scalability settings meet the conditions to respawn a Niagara system.

An example of the scalability settings that easily reproduce this edge case is as follows;

  • Update Frequency is other than Spawn Only
  • Cull Reaction allows respawning, such as Asleep and Clear
  • Significance Handler is Distance, etc., which easily meets Activate/Deactivate conditions.

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Steps to Reproduce
  1. Disable a Niagara component which takes some time until complete (such as Fountain.)
  2. Set View Target to someone/something sitting at a point where the scalability system can disable the Niagara component. (e.g. the Niagara set a short Distance Max limitation like 1000 units and a camera is enough far from the component.)
  3.  Set View Target again to someone/something sitting at a point where the scalability system allows the Niagara component to re-activate.
  4. The Niagara component which has been disabled at step 1 will respawn. (From the developer standpoint, the disabled particle effect comes back unexpectedly.)

I attached a repro project (FXIssueUE53.zip). Please use it. Otherwise, read the description and prepare another repro project.

  1. Download the attached project and open it.
  2. Run PIE and make sure you are seeing a Fountain niagara effect.
  3. Hit 1 key ... the level blueprint deactivates the effect and switch to the camera. 
  4. Hit 2 key ... the level blueprint let you back to the player pawn, but the effect (supposedly already-deactivated) would respawn.

Have Comments or More Details?

There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-198200 in the post.

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Backlogged
ComponentUE - Niagara
Affects Versions5.25.3.1
CreatedOct 17, 2023
UpdatedDec 5, 2023