Particle simulation resets when an emitter goes out of view

[Daw588 (Lain)]

Reproduction Steps:

1. Create a particle emitter
2. Look away
3. Look at it again and observe particle simulation starting from the beginning instead of resuming where it left off

Fire Particles Bug.rbxl (83.9 KB)

For the player, the fire appears to re-ignite for no apparent reason, which is not what I intended when making this fire particle. If this behavior exists for performance reasons, it doesn’t appear to be documented on the ParticleEmitter page.

Expected behavior

Simulation should resume without starting over as it breaks the intended effect envisioned by a developer.

[TaxFraudBruh (johntrivious)]

This is the intended behaviour though…
I do think it should start again around where it was to keep consistency but its still how it is to ensure good performance and its a waste of resources to keep emitters active when they aren’t completely visible.

You also don’t really even notice it at all when you’re playing games, at least in my opinion and from my experience.

[Judgy_Oreo]

I believe this is a known limitation of the current Particle system:

Particles persist forever if you aren't looking at them

Great ideas! The main issue with forward simulating the outdated particles is a potential lag of updating all accumulating particles. With the current system you would need to simulate all missed frames with some precision for the particles to catch up. I like the idea of only forward simulating what can be mathematically calculated without actual simulation. For the context, first we wanted first to fix the crash and getting out of memory with too many outdated particles. The fix is in inter…

Particles persist forever if you aren't looking at them

Will particles being simulated off screen be possible in the future? We are currently exploring the possibility of off-screen particle simulation, assessing what it would entail and how it might be implemented. However, I want to be cautious in setting expectations. There are several unknowns and technical challenges that need to be addressed, and at this time, work on particle features is not a top priority. It is unlikely that this capability will be available by the end of 2023. As for 202…

[music_man1996]

Hey!! Thanks for the report. This seems like intended behavior so going to close ty for the report.

[music_man1996]

I will find a staff member to offer a more detailed response on this one, just to close out the loop.

[jackWorhee (Jack_V)]

This is done to prevent lag. If particles are to keep emitting even when they are not being actively viewed, then it can cause performance issues. That’s why Roblox automatically disables ALL effects as soon as they are not actively visible by the user.

[neutrinostack]

Hi @Daw588,

Thanks for bumping this thread and for your detailed report. Apologies for the delay in getting an official response here.

We can confirm that the behavior you’re seeing – where ParticleEmitter simulations might reset when the emitter goes off-screen – is indeed a current limitation of the Roblox engine. As some users in the thread correctly pointed out, this behavior stems from performance optimizations designed to reduce the engine load by not simulating effects that aren’t currently visible to the player.

Regarding the lack of documentation on this specific point: We understand the frustration when encountering undocumented behavior. Decisions about what to include in documentation often involve balancing comprehensive detail with clarity and focus on the most common use cases and APIs. Sometimes, specific engine optimizations or limitations like this one, which might be considered a more niche case or have less noticeable impact in many gameplay scenarios, aren’t explicitly detailed to keep the documentation streamlined. However, we acknowledge your feedback that clearer information on this would have been helpful.

We absolutely recognize that this limitation can be frustrating, especially when you’re trying to create persistent or seamless effects like the fire example you provided. Improving the particle system, potentially exploring options for handling off-screen emitters differently, is something we internally would also love to pursue.

That said, we also want to be transparent about priorities. While we see the value in enhancing the particle system, addressing this specific limitation is not currently on our immediate roadmap compared to other ongoing engine initiatives.

Thanks again for raising this issue and providing clear examples. We appreciate you bringing it to our attention.