Hasta La Motion!

Two different questions in one here. I’m still fairly new to Nuke, and finding help on alot of things seems to be rather daunting. Anyway, i’ll hope right to it.

1. How does masking with Flares work exactly? I have a flare i need occluding from, say, a ship flying by. How exactly does one use the alpha/rgb/whatever of the ship as the mask to occlude the flare?

2. If anybody’s savvy with expressions, i’m trying to code/work out a way to automatically calculate animated blur/glint brightness/size based on, say, the size of an engine-ball tracking mark, or, maybe the distance of an axis node in 3d space from the camera.

2 is less pertinent for now and, likely, more complicated, but if anybody could help, I’d be most grateful. Cheers!

-Tom