Creating a particle effect with mapping particle color to speed

[warrenhenning]

I'd like to reproduce an effect from an old Maya particle tutorial in Houdini: http://www.thegnomonworkshop.com/tutorials/speed_color/speed_color.html

 

It's for Maya, so he has a per-particle expression that maps particle speed to a ramp.

 

I found a Vimeo video that does this with Houdini: 

 

 

Basically you just apply a VOP to the particle system that takes velocity, gets speed by taking its length, maps it into the range [0,1] with a Fit node, sends that to a Ramp parameter node, then uses that as diffuse color. That part I get and I can do.

 

My issue is getting the actual particle motion to produce the speed shifts that produce the color shifts -- without the turbulent motion in the attached video, you don't really achieve the effect.

 

I don't want it to be per-particle -- more like some kind of turbulence force that jostles groups of particles up and down as they move through space. The original article doesn't state exactly what it is, unfortunately.

 

I tried drawing a curve with jagged lines in the general direction I wanted it to go in, but it didn't really have the acceleration I wanted, and I couldn't figure out how to control the rate at which it went along the curve.

 

I'm also curious as to how to get the glowing, smoky look in the attached video, but getting the particles in sufficient quantities at small sizes should be something I can figure out if I can get the basic motion and color shifts going.

 

Thanks!

color_test_320x.mov

[mestela]

not quite the same, but might give you some ideas.

 

-one way to generate random force pulses through an area

-a colour ramp driven by velocity

-streaks created via a trail

-simple vdb from particles (need to do a mantra render to see the colour transfer)

 

streak_particles_v02.hipnc

 

[warrenhenning]

That's awesome and uses a bunch of nodes I have no understanding of

[warrenhenning]

I've looked again at that video frame by frame and it looks like the same amount of noise gets applied to each particle.

 

I tried modifying the VEX expression in that POP Force node and it's starting to give me what I want! Thanks so much!

 

Now I just need to figure out how to render it all pretty.

Edited November 3, 2015 by warrenhenning

[mestela]

that setup contains an example shader so that the streaks accumulate their colour the way maya streaks do, and the volume should render fine as is. tweak the volume density, etc, should get you in the ballpark.

[Tyfx567]

looks really cool Matt!