Hello artists,


I've been working on the Doctor Strange portal effect and the only problem I have(so far) are the sparks entering the circle which isn't what I want. I tried making a collision object to block them out but I don't know how to render it invisible. Regardless, it seems like a sloppy solution anyway. However, I watched the “Rise FX/Doctor Strange/Houdini Connect” video (https://vimeo.com/217897791) and they said they used “a simple Metaball force to keep the sparks from entering the circle.” I have no idea how this is done but you can see their “example” at time 3:09. Any ideas? Please be thorough as I'm fairly new to Houdini.

Here's my project for context.

Thank you!