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Particle trails not working
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Description

System Information
Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.64

Blender Version
Broken: version: 2.80 (sub 74), branch: master, commit date: 2019-06-05 13:55, hash: rB806d4fbc5e40
Worked: (optional)

Short description of error
Particle trails are not working in the latest build of Blender 2.8.

If I copy the same object into Blender 2.79, everything is working perfectly.

I think recently the particle system got a patch for better handling of multiple threads and large simulations. May be, some issue with that. @Juan Gea (juang3d)

I have attached the blend file.

(Blender 2.8)

Exact steps for others to reproduce the error
Just add a particle system to the default cube and try increasing the trail count.

Details

Differential Revisions
D5034: Remove unused particle settings from UI
Type
Bug

Event Timeline

Did particle trails ever work in Blender 2.8? It looks like no code actually uses the trail_count variable currently.

Was it removed as part of rB51b796ff1528c?

@Brecht Van Lommel (brecht), Since the option is doing absolutely nothing right now, we can also remove it?

Remove it. It was never supported in Cycles or Eevee, and I would consider adding it there a feature rather than a bugfix.

@Brecht Van Lommel (brecht) @Jacques Lucke (JacquesLucke)

But, the default render mode 'halo' is also not supported by Cycles/EEVEE. Anyway invariably we will have to add an object or collection to render the particles. Does it really have to be removed?

I was basically create a few vegetation assets. So, I was just using the trails as a visual aid. Because, otherwise we will have to bake the particles to actually see their path. I found using trails was more interactive and I could finally bake and convert the paths to editable geometry when I am happy with the simulation.

Can it stay just as a visual aid?

There is nothing against adding support for it in the new viewport, but it would not be handled as a bugfix. Until that happens, options that do nothing should be removed.

Turns out there are a lot of options that don't seem to do anything anymore. Almost none of the flags in eParticleDrawFlag is used. But all the options are in the UI still.
I suggest for Blender 2.80 we just remove the python part of these options instead of removing the C code.
If necessary, the C code can be cut out later, or we wait with that until we can remove the entire particle code.

I suggest for Blender 2.80 we just remove the python part of these options instead of removing the C code.
If necessary, the C code can be cut out later, or we wait with that until we can remove the entire particle code.

Agreed.

Jacques Lucke (JacquesLucke) lowered the priority of this task from Needs Triage by Developer to Confirmed, Medium.

Particle trails are not supported currently. The settings for it are not in the ui anymore: rB87fde57b63887aa3082917eebcff5f3f069d610a