Hello everyone! I'm a total beginner to Houdini and this is my first simulation that follows the "Particles Fun" tutorial:
https://www.sidefx.com/tutorials/particles-fun/ [www.sidefx.com]

At the 7:50 mark, the Attribute Create node was used and was renamed to pscale. "$CR" was keyed in under the Value parameters, and the creator explained that this would make the particle sizes decrease over time. This was, at a later point, changed to "$CR*0.1* but in my case, I used "$CR*0.02* for a better desired size.

Nevertheless, I noticed that my particles did not fade over time [drive.google.com], and was wondering what could be the issue here.

I tried to troubleshoot and saw a few users explaining how they used Attribute Wrangle on the forums here.

And so I did that, and while I did notice them fading more, they seemed to wiggle a lot too which made the simulation seem quite noisy [drive.google.com].

This was the expression I used:

float @pscale;
@pscale = rand(@ptnum) ;

@scale = fit01(rand(@ptnum), .001, .02);

Hopefully someone could help to explain what went wrong here. Thank you very much.

A common setup is to normalize age over life. Then you have a percentage (i.e. 0-1) that you can route to a control ramp. The left side of the ramp represents birth, and the right side represents death. This way you can shape growth throughout the life of the particle.

Pops internally generates a normalized age attribute, that is not visible on the geometry
spreadsheet, @nage. So you can use float index = @nage in this case also.




L

Enivob
A common setup is to normalize age over life. Then you have a percentage (i.e. 0-1) that you can route to a control ramp. The left side of the ramp represents birth, and the right side represents death. This way you can shape growth throughout the life of the particle.

Thank you so much for your time! Your approach is easy for me to understand. I would like to ask whether you knew why the $CR expression wasn't working out? I was troubleshooting and read on a forum that the dollar expression variables are being phased out. Is that what was causing the issue?

Thank you again.

It is working. It's just that your particles life has been reached, and the fit you are using is clamping
everything. If you up that fit to 10 or so, you'll see the attribute create is working.

Your simulation starts at frame 1, so by frame 120 a lot of your particles have reached their full age.
But I would stop using attribute create, as it's single threaded. Just scrubbing the timeline using
a wrangle is about 20x faster compared to the attribute create. That SOP is verrry old, and the use of
$ type variables is also verrry old, you don't want to use this method at all.

Instead, just use a wrangle after your point VOP,

f@pscale = @Cd.r * 0.02


You point VOP mapping vel to Cd doesn't need a vectofloat, the length VOP is already spitting out a float value btw.


L

tinyhawkus
It is working. It's just that your particles life has been reached, and the fit you are using is clamping
everything. If you up that fit to 10 or so, you'll see the attribute create is working.

Your simulation starts at frame 1, so by frame 120 a lot of your particles have reached their full age.
But I would stop using attribute create, as it's single threaded. Just scrubbing the timeline using
a wrangle is about 20x faster compared to the attribute create. That SOP is verrry old, and the use of
$ type variables is also verrry old, you don't want to use this method at all.

Instead, just use a wrangle after your point VOP,

f@pscale = @Cd.r * 0.02


You point VOP mapping vel to Cd doesn't need a vectofloat, the length VOP is already spitting out a float value btw.


L

Many thanks for your response