Glasses get their own controller over the MCU (permission, 120 Hz default, brightness, volume, sunblock, 2D/3D) and the game moves onto them when plugged in. The IMU drives Cardboard head tracking and the SteamVR driver. 3D falls back to one eye's view on phones that can't send the 3840x1080 signal. Options open from a glasses button in game and on the Steam page.