Using Cardboard SDK is surprisingly easy. It’s automatically creating two cameras for both eyes, the job is making a standard FPS. I already had experience with game controller support, so my hardest task was the actual level design, also testing. Using Cardboard a lot made me motion sickness. I don’t think virtual reality on mobile is bearable more than a few minutes long experience. (Or it’s just my phone.) I had to find some tricks to prevent it, like disable side moving, setup proper player height, physic factors and add a reference frame.
I’m happy I could come up with something in time, it’s very buggy but at least it’s working and I learnt a lot about terrain and level design. Available on Google Play.