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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.
Screenshot of model

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.

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  • $\begingroup$ If you are using the compositor, an invert node can swap the alpha areas of a shadow only layer. What render engine you use will determine what material options you have. $\endgroup$
    – sambler
    Apr 21 '17 at 3:58
  • $\begingroup$ @sambler - I used your suggestion. I followed some tutorials about rendering only shadows, and used an invert node, which worked. Thanks for the help! $\endgroup$
    – Khart99
    Apr 24 '17 at 16:57
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put this into your compositor 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 compositor v2 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

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  • $\begingroup$ Thanks for the screenshots! This is what I've been trying to do, but couldn't figure the nodes out to do it. Thanks!!! $\endgroup$
    – Khart99
    Apr 24 '17 at 16:59

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