How to get shadows information in cycles I have a WIP looking like this



Now I want to do something about a background and I want to do it in a similar halftone style. But when I'm applying it the same way as I did on the models, the dots are covering the shadow. 

I need a shadow information, to influence them somehow, but I have no idea how to extract it. I'm using Cycles.
Ok, so  I achieved the result I wanted. Unfortunately, it's not fully procedural. What I needed to do was to bake shadow map of the plane and than I could use this information to make a final artwork.