Render plane only where spotlight hits, rest should be transparent I have a block with a logo cut out through it, and I'm shining a spotlight down through it so it shines on the plane below.  I'm trying to render it so the plane is transparent, except where the light hits it. I'd like the logo block to render as well.


I'd like the blue plane to render transparent, and only render where the light hits the plane.

I've seen other posts about how to only render shadows on a plane, but not the opposite, rendering on light on the plane.
I've played with render layers, trying to set a certain color to alpha (like the dark colors) and I'm not having luck yet.
use the color of the non-lit plane for the 'Key Color' attribute.

this makes everything transparent that's with the same color. if your logo also gets transparent then just wait a bit, i'll create a more complicated but better working compositor for you.

Edit: here's the better compositor

for this one you need to also set the plane's pass index to 1

and check the render layer's object index

I can't add more than 2 images so you need to use google for the last part