Particle effect library no longer renders correctly when camera is moving

Reproduction Steps
This rain effect is used broadly across Roblox experiences: Rain Module + Plugin

The file to reproduce:
RainParticleBug.rbxl (48.1 KB)

Expected Behavior
The effect should render as expected when the camera is moving and when it is still. It should produce a dense layer of particles in the scene simulating real-life rain.

Actual Behavior
When the camera is moving, the longer-lived particles of the rain effect are no longer distributed uniformly and render only in specific places. This breaks the immersion of the effect and makes the effect not usable since players constantly move their camera.

I can reproduce this effect in Studio on the given file.

It only happens when the camera is rotated, not while zooming it seems.

Issue Area: Engine
Issue Type: Display
Impact: High
Frequency: Often


@JaapSuter Actually, looking into this a bit more, what I’m doing when the camera rotates/moves is that I’m repositioning and resizing a box around the player’s camera:

Perhaps the recent particle changes are using a deterministic (non-seeded) starting pattern whenever the particle emitter’s parent is resized?

EDIT: yes, this seems to be the issue, notice how I’m resizing a standard part with a particle emitter in it and the same issue occurs:


Thanks for this, I’m taking a look right away!


Sorry, just saw this tweet chain:

Looks like it’s the same issue.

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Glad that you finally made a report on this, it’s been affecting it ever since it was released a couple of days ago, hopefully it’s fixed soon!

I just flipped the flags that are likely to fix this problem, if it doesn’t, don’t hesitate to send me a message right away!


Looks fixed, thanks for the help!

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