VFX Graph particles flickering in Alpha Blend Mode

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Hi ! Does anyone know how to fix this ? Basically, the particles of the VFX Graph work just as expected until using the Alpha Blend Mode in the Output Particle Quad. That's when the particles start flickering like in this video. It is working just fine when using Opaque or Additive Blend Mode.

I tried removing each and every other blocks but it's still flickering. Removing the Set Angle block reduced most of the flickering (only a few particles still flickering), but it's still quite noticeable.

Also, I tried reinstalling HDRP, and I am using Unity 2019.3.13f1 (which I updated a few weeks ago).

I also get these errors, I don't know if it's related :

Could not extract GUID in text file Assets/VFXDefaultResources.asset at line 17. UnityEditor.EditorApplication:Internal_CallUpdateFunctions()

Could not extract GUID in text file Assets/VFXDefaultResources.asset at line 19. UnityEditor.EditorApplication:Internal_CallUpdateFunctions()

Broken text PPtr. GUID 00000000000000000000000000000000 fileID 11700000 is invalid! UnityEditor.EditorApplication:Internal_CallUpdateFunctions()

Thank you for your help :) !

https://youtu.be/xI5GlrDCmYM!

Answer 1

Answer by BotsOP · Feb 07 at 01:40 PM

Click on your output particle node then go to the inspector look for sort under particle options and turn it off.

screenshot-1.png (57.8 kB)

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Answer 2

particles rendered additively, look pretty much the same regardless of the order you draw them in, as 2 particles would both add color to existing screen color, ending up with the same end result, However with blended mode the end result is different depending on rendering order. So you have to make sure that the particles are either separated enough in Z-space that they won't keep swapping z position, or that the particles are sorted ( adding performance overhead for sorting ) Check here for detail on changing shader graph sorting. https://forum.unity.com/threads/shader-graph-shaders-and-particle-sorting-fudge.746822/

For regular particle system there are also options for particle sorting on the Renderer. But just be aware of extra performance cost. Note:.. the sorting is within that particle-system, and it won't sort between different particle systems. So if you have 2 different particle systems at roughly the same Z position you might get whole particle systems flickering behind each other... keep them separate in Z. use the sorting fudge or layering to draw certain particle systems later.

Answer 3

Answer by Erans2 · May 26, 2020 at 04:55 PM

Thank you for your answer @JonPQ! I don't think there is a way to use a shader on a VFX Graph particle, is there ? I'll try to find a way to seperate them.

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JonPQ · May 26, 2020 at 05:56 PM 0

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I mean you can change render type, alpha / additive etc... I'm not sure if they do any sorting though... in vfx graph... I would guess not. So if you can get away with additive. that might hide the sorting flickering. I'm still not quite sure of your flickering issue as the video you linked gets 404 error

Erans2 · May 26, 2020 at 06:06 PM 0

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@JonPQ The video had a problem uploading for some reason but here it is : https://www.youtube.com/watch?v=xI5GlrDCmY$$anonymous$$ Using the blend mode Additive does fix the problem but it's not like alpha... I'm trying to make grass, that's why I want to use the alpha.

JonPQ Erans2 · May 26, 2020 at 07:58 PM 0

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saw the video, tthanks. hat does look pretty strange, looks like flickering between 2 different positions, or drawing and not drawing on alternate frames..., but additive mode fixed things.? hmmm do you have back-face culling options ? if so, try turning that off.

Erans2 JonPQ · May 27, 2020 at 01:56 PM 0

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I don't know if I have back face culling turned on, can you tell me where the option is ?

Answer 4

Answer by dyfer · Aug 13, 2020 at 07:47 AM

A page is open for voting on unity issue tracking if you want this bug fix : https://issuetracker.unity3d.com/issues/gpu-sorting-outputs-flicker-when-setting-alive-selectively-and-sorting-is-on

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VFX Graph particles flickering in Alpha Blend Mode

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