When spawning GPUCompute Sim Niagara system which is consist of opaque particle emitter and translucent one, if those emitters use Collision module, opaque particle often appears one frame later than a translucent one.

Here's an animated GIF. (Note: This movie is made by special way to highlight the issue, recording the screen and editing as frame-by-frame playback video.) [Image Removed]

If it's CPU Sim or without Collision module, this issue does not occur, meaning all particles appears at the same frame.

[Image Removed]


Steps to Reproduce

This bug occurs in a split second, so it's recommended to record with OBS studio (with the recording rate set to 60fps) and check it by frame-by-frame playback.

  1. Create an opaque surface material and a translucent one.
  2. Create a new Niagara VFX.
  3. Place two emitters, based on fountain template or something else.
  4. Set Sim Target to GPUCompute Sim.
  5. Add Collision module. 
  6. Use the opaque material for one emitter and the translucent one for the other emitter.
  7. Make a level blueprint to spawn this Niagara VFX in a map.
  8. Press Alt+S to run simulation.

Limiting max fps (e.g. t.MaxFPS 10) can help to watch this visual issue.

The repro project is available on the attachment. LV_WithCollision spawns Niagara VFX which has those two emitters with Collision module. LV_WithoutCollision spawns the exactly same Niagara VFX except for Collision module. Also, the frame-by-frame playback GIF animations are attached.

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ComponentUE - Niagara - Content
Affects Versions5.4.1
CreatedApr 2, 2024
UpdatedJun 6, 2024
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