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Flip Reseed Flicker Problem Thread - Gas Seed Marker

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If you're flip simulation flickers from using reseeding particles this threads for you.

TLDR: I've found a temp solution but want a better one. Inside the flip solver search for a node called "Gas Seed Markers"(Its renamed to "Reseed Particles") Uncheck the "Build Inside Surfels". This will stop the popping but maintain the effect of deleting the unnecessarily dense overlapping particles. 

 

Starting this thread for myself to document my thoughts on this but also for anyone else who needs reseeding to keep their simulation in check. So far I have a temporary solution to my issue but I want a better one. My hope is that we can discuss a better means of achieving the desired result of consistent fluid particle density without flicker or popping. 

The masterclass doesn't explain reseeding and I couldn't find much on the topic in forums or elsewhere for how it works. The node responsible is Gas Seed Markers(GSM form now on). It checks the number of particles per voxel within the surface field for inside the fluid and outside within a given number of boundary voxels and does three things. 

A. When particles exceed the desired density per voxel GSM will cull the points of that voxel.

B. If voxels beneath the surface do not have the correct density GSM will add points.

C. If there are not enough particles on the surface, within 2-3 voxels GSM will fill that voxel with the desired number of points per voxel. 

 

It seems on one frame the GSM node will delete ALL particles within a voxel that exceeds the limit. Then the next frame, because the void was created it will then repopulate the void with the desired density.

So this is where I'm hoping for some help in understanding, in order it's:

1. GSM determines particles are too dense.

2. GSM deletes all particles in voxel. 

3. Complete solve (particles partially close in on this void)

4. Next Frame of solver - void still exists so GSM adds particles to this voxel with points = Flicker / Pop. 

 

So to start the thread:

First - Does Gas Seed Marker delete all particles within a voxel that exceeds the density limit or is this an optical illusion?

Second - I'm having trouble getting this node to function outside the context of the flip solver. I want to see it populate points into the Geometry data but it has a lot of requirements regarding the slice index that I don't fully understand. If anyone has or can create a working example of this node functioning outside the context of the flip solver I would greatly appreciate it.

For now I'm going to try using two GSM nodes one after the other. The first only performs the cull operation and the second performs the fill before processing the solve. Will post back with results shortly. 

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Okay so using two GSM nodes has a far smoother result as it does not produce the kind of popping and bubbling HOWEVER, it does still present a problem in that the particles it seeds are random. Kind of like staring at a scatter sop with the seed set to $F and hitting play. 

I need a way to reproduce the function of the GSM node without completely deleting all points within that voxel. I need it to leave the desired density behind.

 

Has anyone played around with custom reseeding tools or density control using sop solvers inside their simulation?

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