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particle velocity over life worldspace issue

If you create a particle with Initial velocity (localspace)

 x50, y50, z300
 x-50, y-50, z100

They will spray away from their spawn point, hit the right wall, they go left, hit the floor they go up, cieling they go down. That works and is correct as expected, but then add velocity over life (worldspace, not absolute) and things get a bit wacky.

 in 0
 x1, y1, z1
 in 1
 x1, y1, z-2

they should start to fall towards the ground in worldspace regardless of their initial local velocity

but they don't, they act weird

  • ones on the floor spray up then fall down (good)

  • ones on the ceiling spray down then fall up (bad)

  • ones on the walls spray outwards then kinda continue to float in the same direction (wtf)

Product Version: UE 4.15
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asked Mar 09 '17 at 03:58 PM in Bug Reports

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avatar image AndrewHurley Mar 14 '17 at 06:57 PM

Hey Taisaku,

Thanks for taking the time to post this question. We will begin investigating soon and we appreciate your patience while testing occurs.

Let us know if you have further questions or need additional assistance.


Andrew Hurley

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2 answers: sort voted first

Hey Taisaku,

I didn't reproduce this behavior here are the steps for the test I ran:

  • Open a blank project

  • Create a new particle system and open in cacade

  • Change the initial velocity to the values given in the OP

  • Add a velocity/Life module and change values to those given in OP also check "In world space"

  • Save and drag particle system into the scene

  • Rotate the particle system to different orientations to confirm expected behavior

No matter what orientation was used the particles would accelerate in the -z direction which is expected. The initial movement would clearly orient according to the emitter's rotation as well suggesting it was in local space as expected.

If I need to adjust my steps let me know, I would recommend following my steps to see if you get the same results.



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answered Mar 16 '17 at 08:40 PM

avatar image Neros_ Mar 17 '17 at 02:21 AM

it might have something to do with the spawn orientation, my particles are being spawned using hit normals. Is there a way i can export my particle system for you?

avatar image Ed Burgess ♦♦ STAFF Mar 17 '17 at 03:38 PM

No need to send me anything thank you though. I did some additional testing and have reproduced this issue. You will find a report for it here: https://issues.unrealengine.com/issue/UE-43018

You can track the report's status as the issue is reviewed by our development staff. Please be aware that this issue may not be prioritized or fixed soon.

For now I would recommend using the Const Acceleration module with a negative z (maybe -300) since this seems to work in world space fine.


Ed Burgess

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How to make it work:

• Don't add Initial Velocity. • Add Velocity/Life and mark Absolute and In World Space. The Velocity/Life will control the velocity.

This makes it always go in the direction you want in the World.

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answered Apr 04 '19 at 05:00 PM

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