Ex-Zodiac now has an itch.io page!

Thanks!

The shadows are done using an orthographic camera that views the level from a top-down perspective and it follows the ship as it moves through the level. The camera is inside a viewport so that I'm able to access what the camera sees as a texture. The viewport is setup to have a transparent background, and things like the ground in my levels are on a different visibility layer so that they're not rendered by this camera, only the main objects such as the ship, enemies, scenery etc are.  I then use this texture mapped onto a flat plane positioned just above the ground (also on a different visibility layer so the top-down camera doesn't see it) and I use a shader to draw the checkerboard effect. Any part of the viewport texture with a transparency < 0.5 is discarded, and anything greater is where I draw the checkerboard texture, which is just a repeating 8 x 8 texture and it's drawn using screen space UVs. 

Hope that helps, let me know if you're unsure of anything :)

I'm having to prepare a demo for EGX in October, so I imagine I will release that demo online shortly afterwards :)

Thanks! Hopefully I can get back to working on it soon :)