Tracking Matte in FCPx

Good Morning! I am trying to place dust particles which is an overlay (layer 3) ONLY in a beam of light (layer 2) that sits on top of the BG (layer 3).  In Premiere, I do this by creating a Tracking Matte but in FCPx I am not sure how to do this as I have struggled for days.  Any help would be appreciated.  Thanks!

1: export the layer to Motion. Try Motions tracking tools  (located in behaviours) and fantastic (fun) particle emitters.
2: I you want do the job within FCPX get some Coremelts Mocha powered plugins, i.e: Drive X . Visit their website and have a look to video tutorials.

I believe you asked me this in a private message on Linkdin. You mentioned something about setting the Blend Mode to luma stencil. If your using something like MotionFVX's dust particle clips, what you want to do is set Blend Mode to Screen.


Motion's own tracking tools are actually pretty good with the right content.
support.apple.com/guide/motion/intro-to-...ing-motn18191fa3/mac

This is what I am trying to do in FCP. 

I am not familiar with that product, but I use similar overlay clips from MotionVFX, and it's the same process.  Set the Blend Mode (Add, Overly, Screen, etc) to get the effect you want.  What I'm used to working with is a clip of dust or light rays, on a black background, with no alpha channel.

Good Morning! Ben thanks for taking the time to help me.  I really appreciate that.  So I have attached exactly what I am trying to understand. Is there a way in FCP to use the light from the light rays layer as a luma matte to define where the dust particles should go.

Layer 1 - BG
Layer 2 - Light Rays on black BG and blend mode set to screen
Layer 3 -  Dust Particles on a black BG blend mode set to screen

In this set up, the dust particles cover the whole frame.  I understand that I can mask in the dust particles but is there a way similar to Premiere Pro of using a Luma Matte Track effect to accomplish the same.

I probably am making this more complicated than I need to but that is what I am asking.  That way do not have to worry about creating a tracking mask as the position of the light rays changes.

Hope this helps.