Jump to content
Hyrulean

Pop Grain issue! Please help!

Recommended Posts

I've been stuck on this for a couple of days now and would love to hear you guys' input.

I have close up shot were a character's feet is pushing through snow up to his ankles.

I decided to try grains for this (it's my first time really using it) and to get the snow together I used the constraints set outside in the grain source.

Mostly the sim is working as intended but I'm getting a lot of unwanted fast movement from some particles (as if they're trying to keep the constraint but not really keeping it, so they pop in and out, and that results on a flickering on the meshing.

Did anyone come around this problem before? I am up for any solution at this point, even trying another method.

 

Share this post


Link to post
Share on other sites
2 hours ago, Hyrulean said:

I've been stuck on this for a couple of days now and would love to hear you guys' input.

I have close up shot were a character's feet is pushing through snow up to his ankles.

I decided to try grains for this (it's my first time really using it) and to get the snow together I used the constraints set outside in the grain source.

Mostly the sim is working as intended but I'm getting a lot of unwanted fast movement from some particles (as if they're trying to keep the constraint but not really keeping it, so they pop in and out, and that results on a flickering on the meshing.

Did anyone come around this problem before? I am up for any solution at this point, even trying another method.

 

Maybe you can try a POP Wrangle to « clamp » the speed of particles ?

Another thing you can try is to simulate like you do as a first pass, then use CHOPS to clamp or filter/smooth the channels of positions. I use that with RBD sometimes, but with lots of points, it may be heavy...

Edited by StepbyStepVFX

Share this post


Link to post
Share on other sites
1 hour ago, StepbyStepVFX said:

Maybe you can try a POP Wrangle to « clamp » the speed of particles ?

Another thing you can try is to simulate like you do as a first pass, then use CHOPS to clamp or filter/smooth the channels of positions. I use that with RBD sometimes, but with lots of points, it may be heavy...

I used a pop speed limit with a lower and higher speed, would that be the same as using a pop wrangle for it right?

I never used chops, do you know any place where I can learn to do that?

Share this post


Link to post
Share on other sites
8 hours ago, Hyrulean said:

I used a pop speed limit with a lower and higher speed, would that be the same as using a pop wrangle for it right?

I never used chops, do you know any place where I can learn to do that?

In this case, that’s simple :

- create a NULL after your sim, this where you will fetch the translation data of each point

- create a CHOP network

- inside the CHOP network, create a Geometry CHOP node, set it to fetch the animated tx, ty and tz and make it point to the NULL sop node you added inside your network. I let you look at the tutorial below to look at how to set it up correctly (you need to adjust some parameters like the frequency at which you sample the channels etc.)

- add a filter node, that will « blur » your channels. You can adjust the width of your smooth filter.

- back to your sop network, add a Channel node after the null, to fetch back the translation channels of each points.

Basically, what is does, is that it takes the translation (position) of each points and consider it like a « signal » / curve. Then you can do signal processing on those curves, in that case you can smooth it. Then you re-export that and it will override the initial position of each point.

Bear in mind that smoothing will kill the popping/flickering of your particles, but it will affect all other particles as well, so you need to apply that only to your popping particles. And be carefull when deleting particles : make sure you identify the particles consistently over the frames of your animation : to build the curves, the chopnet needs consistent id values over the range of sampling. Otherwise, you will mix positions of different particles and/or re-apply smoothed channels to the wrong particles and it will mess everything.

Selecting the right particles to smooth the movement maybe probably the trickiest part :-)

 

Share this post


Link to post
Share on other sites

Also grain has a built in speed and acceleration limit you can use. And uping the drift threshold might help with you sim as well. 

grain_parms.PNG.374124e7ddc5f3b9715a45019f49d7f5.PNG

Share this post


Link to post
Share on other sites
On 6/20/2018 at 10:07 PM, StepbyStepVFX said:

In this case, that’s simple :

- create a NULL after your sim, this where you will fetch the translation data of each point

- create a CHOP network

- inside the CHOP network, create a Geometry CHOP node, set it to fetch the animated tx, ty and tz and make it point to the NULL sop node you added inside your network. I let you look at the tutorial below to look at how to set it up correctly (you need to adjust some parameters like the frequency at which you sample the channels etc.)

- add a filter node, that will « blur » your channels. You can adjust the width of your smooth filter.

- back to your sop network, add a Channel node after the null, to fetch back the translation channels of each points.

Basically, what is does, is that it takes the translation (position) of each points and consider it like a « signal » / curve. Then you can do signal processing on those curves, in that case you can smooth it. Then you re-export that and it will override the initial position of each point.

Bear in mind that smoothing will kill the popping/flickering of your particles, but it will affect all other particles as well, so you need to apply that only to your popping particles. And be carefull when deleting particles : make sure you identify the particles consistently over the frames of your animation : to build the curves, the chopnet needs consistent id values over the range of sampling. Otherwise, you will mix positions of different particles and/or re-apply smoothed channels to the wrong particles and it will mess everything.

Selecting the right particles to smooth the movement maybe probably the trickiest part :-)

 

Thanks man! This worked pretty well!

Share this post


Link to post
Share on other sites
14 hours ago, Hyrulean said:

Thanks man! This worked pretty well!

CHOPS are slow and sometimes complicated (not too many tutorials over there), but once you dive inside, it really opens new possibilities ! I really love chops !

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×