Wow this brings back some memories! I spent a long time doing research in this area. You can do very cool stuff by realizing that spatial light pattern propagates as Fourier transform with a "spherical" term in the integral (having a perfect convex lens at the focal point cancels this term, hence Fourier transform. Also if laser propagates to sufficient large distance, the term vanishes. A lensless, diffractive projector will always be in focused).

Note that you need a coherent, planar light source like an expanded laser beam.