Opacity from Attribute Transfer

[jonjonmakemake]

Hello, 

 

I have having trouble with a particle effect and I can't find anything on how I would achieve it. I have a rough idea of how it might work but my houdini knowledge and experience isn't good enough to actually do it. 

 

I am trying to create the effect of an illuminated object flying through a room full of particles, like dust in a warehouse. I want the particles to initially be invisible and only when the target object passes by for the particles to become visible and then begin to glow.  So far I have a set up where the target object flys through the scene and collides with the particles. As it does this I have an Attribute transfer that gives me a field of influence that I want to drive the visibility of the particles. Does anyone now how I could do this? 

ParticlesTest_v032.hip

[jeremiah]

Hi, couldn’t check hip file yet. Just wonder if you can do it after the sim? Attribute transfer red color from target obj to ur simulated particles. and in point wrangle say, “@Alpha = @Cd.x”. 

[jamesr]

There's a few ways to do this. Here is a simple one using a SOP Solver in the AutoDopNetwork. This way allows a nice fade in/out over time by accumulating a value into an attribute called "illume". The disadvantage of doing the fading like this in a SOP solver is that you need to sim each time you want to adjust the fading. Alternatively, you could also store the frame where the sphere first contacts or has enough influence on a particle, and then post-sim use that to control fading on/off. Changed/added nodes in gold.

ParticlesTest_v032_jamesr1.hip 

 

ParticlesTest_v032_jamesr2.hip

Edited October 25, 2019 by jamesr
Actually here's both