Bug Metal: Particle System glitches when rendering another ParticleSystem to offscreen RenderTexture

When I have Particle System "A" only rendering with my main camera, it glitches out, often to the point of a fullscreen cross, when I am also rendering a Particle System "B" only to another camera that targets a separate render texture. This bug seems easiest to reproduce when the Particle Systems use the Trails module. Any idea what is going on here?

Bug occurs on Mac and iOS devices (A7, A9), but not in play mode in the editor.
Unity 2019.3.15f1 Metal, URP 7.3.1
Unity 2019.4.1f1 Metal, URP 7.3.1

EDIT: also occurs in Mac standalone with Graphics API Metal, but not OpenGLCore

 

The problem seems to go away if I enable Graphics Jobs. Without Graphics Jobs, it seems to be linked to low performance situations, like when I am running a standalone build and I am also building lighting in the editor.

 

Hi! I have the same issue on Android using Vulkan API, but with OpenGLCore everything is ok. With LWRP it also worked fine

 

Perfect that also seems the solution to my problems.
Even if i dont even know what it exactly does.

 

Great. I'm glad it works for you too.
I tried many things while trying to unsuccessfully make a small test case to submit to unity. Once I saw that a heavy CPU load could cause the particles to stretch across the screen (when also rendering other particle to a RT), I thought the Graphics Jobs might work, by offloading the particle setup work from the main CPU, that is getting overloaded, to other cores, which is the theme of Graphics Jobs.

 

Did you manage to file a bug report, chrismarch?

I believe I'm experiencing the same issue. We are doing a very UI-heavy game and have almost everything rendering exclusively to render targets. And we're also seeing this issue with particles glitching out into big white flashes on Metal (Mostly iOS though we have seen the particles glitching in the Editor scene window occasionally).

We're using Unity 2019.3.0f6 with URP 7.2.1

FYI, enabling the graphics jobs did make the glitching go away, but we ended up getting other weird rendering bugs (e.g. skinned characters missing their faces, as well as crashes).

Did you end up with stability and/or other rendering issues too?

EDIT: Another way I've gotten around the issue is by turning multi-threaded rendering off (and not using graphics jobs either).

 

Hello,

Yes I opened a ticket a couple weeks ago.
The bug is no longer reproducible in "trunk" as of July 8th, and there was a ticket to backport to 2019.4.
I don't have an issue tracker link for this issue unfortunately, but I suppose it should be fixed in the latest 2020 beta.

Thanks for the tip with multi-threaded rendering.

 

Oh, terribly sorry. I didn't realise you replied.

Thanks for opening the ticket.

BTW, any idea if it's been / being fixed in 2019.4?

 

No ETA, I guess there is a long backlog of backports

 

Have the same issue with Unity 2019.4.14f1, tried to use only OpenGLES2, OpenGLES2+OpenGLES3, OpenGLES2+GraphicsJobs, OpenGLES2/OpenGLES3+GraphicsJobs, but still unsuccessfully

 

There seemed to be a bug related to this that was address in 2019.4.13f1:

Particles: Fixed uninitialized compute buffer access when using particle quads and gfx jobs (1274445)​

Haven't actually tested this myself yet.

 

It's been fixed in 2019.4.27

https://issuetracker.unity3d.com/is...rendering-a-particlesystem-to-a-rendertexture