ok so im trying to learn the attribute and vex in houdini, I already know java so the coding part is not a problem for me. I setup a project in mind for myself. I wanted to create a noise pattern on a sphere but only want the noise pattern to show up when a particle from the popnet hits the sphere. I thought about changing the color on the particle and then getting the coordinates from that particle when the color changes to “red”, hopefully it would be the same coordinates on the sphere, then using the coordinates to add noise at that specific location. Now i'm not sure if this is possible. But so far i figured out how to change the color of the particle to red when it hits the sphere, and where the coordinates are at. But how do i go from there, can someone steer me in the right direction?

There are lots of ways to achieve this kind of effect. Here are just some that come to my mind:
Probably the easiest is to use the Attribute Transfer Node and transfer Cd based on the distance of your particles to the sphere.

• Attribute Transfer Node [www.sidefx.com]
  

Or if you want to use VEX check out the help for these functions:

• nearpoints() [www.sidefx.com]
  
• minpos() [www.sidefx.com]
  
• xyzdist() [www.sidefx.com]
  

If you want to learn more about VEX make sure to check out cgwiki [www.sidefx.com] in case you haven't already!