Transparent Reflective floor in Cycles?

For a motion graphics project using cycles, I’d like to create a semi-transparent floor object that reflects ONLY the objects in the scene, and renders as a transparent material otherwise.

The effect wold look something like this:


The above image was achieved by duplicating the objects, flipping them below an imaginary floor, and rendering the flipped objects on a separate render layer. This is not ideal.

Ideally, there would be a clever material node setup in cycles that could make a floor object that would have this effect, but so far all my results just look like this:

How can I make the rest of the floor material become transparent in cycles, so that only the reflections of solid objects are opaque?

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how about making the floor like a piece of glass !

salutations

Wouldn’t a holdout node mixed in with a glossy node according to a lightpath combination help? I think the whole point of the holdout node is to mark areas as zero alpha for things like compositing.

I suggest using a variation of the shadow method proposed by BAO2. The shadow results are great.

Keep in mind it is a composite node setup and not a material node setup. Not sure if that will work for you.

Seems like maybe it has to do with ray length. That is the only one that seems to make it work sorta.
edit: based on Ace Dragon’s suggestion

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This is a machine killer if you have a more complex scene than a monkey. :frowning:
Good try though.

Sooooo… has anyone come up with something? This seems to be an important task… it seems like I have to do something like this once or twice a week now and I’d like to use cycles.